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Published 2 months ago • verified publisherappfluent.usDart 3 compatible
SDKFlutter
PlatformAndroidiOSLinuxmacOSwebWindows
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A package for building dynamic UIs in Flutter using an expressive, XML based markup language.

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Note: This document is very much still a work in progress. #

What is XWidget? #

XWidget is a not-so-opinionated library for building dynamic UIs in Flutter using an expressive, XML based markup language.

That was a mouth full, so let's break it down. "Not-so-opinionated" means that you're not forced to use XWidget in any particular way. You can use as much or as little of the framework as you want - whatever makes sense for your project. There are, however, a few Best Practices that you should follow to help keep your code organized and your final build size down to a minimum.

An XWidget UI is defined in XML and parsed at runtime. You have access to all the Flutter widgets and classes you are used to working with, including widgets from 3rd party libraries and even your own custom widgets. This is achieved through code generation. You specify which widgets you want to use and XWidget will generate the appropriate classes and functions and make them available as XML elements. You'll have access to all of the Widgets' constructor arguments as element attribute just as if you were writing Dart code. You'll even have code completion and access to Widgets' documentation in tooltips, if provided by the author, when you register the generated XML schema with your IDE.

For example:

<Column crossAxisAlignment="start">
    <Text data="Hello World">
        <TextStyle for="style" fontWeight="bold" color="#262626"/>
    </Text>
    <Text>Welcome to XWidget!</Text>
</Column>

Important: Only specify widgets that you actually use in your UI. Specifying unused widgets and helper classes in your configuration will bloat your app size. This is because code is generated for every component you specify and thus neutralizes Flutter's tree-shaking.

Table of Contents #

  1. Quick Start
  2. Manual Setup
  3. Example
  4. Configuration
  5. Code Generation
  6. Inflaters
  7. Dependencies
  8. Model
  9. Fragments
  10. Controllers
  11. Expression Language (EL)
  12. Resources
  13. Components
  14. Tags
  15. Best Practices
  16. Tips and Tricks
  17. Trouble Shooting
  18. FAQ
  19. Roadmap
  20. Known Issues

Quick Start #

This Quick Start guide will help you get up and running with XWidget in just a few minutes. For a more comprehensive description of the various components and features, please see the sections below.

  1. Install XWidget using the following command:

    $ flutter pub add xwidget

  2. Initialize your project by running:

    $ dart run xwidget:init --new-app

    This will create and configure all the components required for a simple XWidget application. It will overwrite main.dart, pubscpec.yaml and existing XWidget specifications, configurations, colors and string values. If you don't want to overwrite these files, run the following non-destructive initialization command:

    $ dart run xwidget:init

    The non-destructive command is intended for advanced users that want to add XWidget to an existing project. For those users, follow the Manual Setup guide starting with step #4. Everyone else should continue to step #3 in this guide.

  3. Register the generated schema file xwidget_scheme.g.xsd with your IDE under the namespace http://www.appfluent.us/xwidget. This will provide validation, code completion, and tooltip documentation while editing your fragments.

  4. To register additional Flutter components, simply modify lib/xwidget/inflater_spec.dart and run:

    $ dart run xwidget:generate --only inflaters

  5. Install the Flutter XWidget plugin for Android Studio. This step is optional, but recommended. It provide EL syntax highlighting, contextual navigation, component generation and more.

    See Inflaters, Components and Fragments for more information.

Manual Setup #

This Manual Setup guide primarily exists to give you a deeper understanding of how XWidget is configured. It is recommended that you refer to the Quick Setup guide to setup a new project.

  1. Create an inflater specification file. This is a Dart file that tells XWidget which widgets and helper classes you intend on using in your fragments. While this fill can live anywhere under the lib folder, we recommend placing it under lib\xwidget and naming it inflater_spec.dart. See Recommended folder structure. See Inflaters for more about inflaters.

    // lib/xwidget/inflater_spec.dart
import 'package:flutter/material.dart';
   
const inflaters = [
  Column,   
  Container,
  Text,
  TextStyle, 
];

  2. Create a custom configuration file. This is an XML document that configures the inputs and outputs of XWidget's code generator. By default, XWidget looks for a file named xwidget_config.yaml in the project's root folder. Make sure that sources contains the location of the inflater spec you created in step #2. See Configuration for more.

    # xwidget_config.yaml
inflaters:
   sources: [ "lib/xwidget/inflater_spec.dart" ]

  3. Generate inflaters and fragment schema. By default, all generated Dart files are written to lib/xwidget/generated. The schema file is written to the project root as xwidget_schema.g.xsd. See Code Generation for more.

    $ dart run xwidget:generate

  4. Register the generated schema file xwidget_scheme.g.xsd with your IDE under the namespace http://www.appfluent.us/xwidget. This will provide validation, code completion, and tooltip documentation while editing your fragments.

  5. Register the generated components in your application's main method. You'll need to import XWidget and the generated code.

    import 'package:xwidget/xwidget.dart';
import 'xwidget/generated/inflaters.g.dart';
   
main() async {
   WidgetsFlutterBinding.ensureInitialized();
    
   // load resources i.e. fragments, values, etc.
   await Resources.instance.loadResources("resources");
    
   // register XWidget components
   registerXWidgetInflaters();
   ...
}

  6. Modify your project's pubspec.yaml and add resources/fragments/ and resources/values/ to assets. There's no need to add each individual fragment; however, if you use fragment folders, you'll need to add each folder here. See Resources for more.

    flutter:
  assets:
    - resources/fragments/
    - resources/values/

  7. Create your UI fragment. By default, XWidget looks for fragments under resources/fragments. Fragments are XML documents that are "inflated" at runtime. See Fragments for more.

    <?xml version="1.0"?>
  
<!-- resources/fragments/hello_world.xml -->
<Column xmlns="http://www.appfluent.us/xwidget">
    <Text data="Hello World">
        <TextStyle for="style" fontWeight="bold" color="#262626"/>
    </Text>
    <Text>Welcome to XWidget!</Text>
</Column>

  8. Inflate your fragment. Where ever you want to render your fragment, simply call XWidget.inflateFragment(...) with the name of your fragment and Dependencies object. See Dependencies for more.

    // Example 1
Container(
  child: XWidget.inflateFragment("hello_world", Dependencies())
)

    // Example 2
@override
Widget build(BuildContext context) {
  return XWidget.inflateFragment("hello_world", Dependencies()); 
}

Don't forget to install the Flutter XWidget plugin for Android Studio. It provides EL syntax highlighting, contextual navigation, component generation and more.

Example #

Please see the example folder of this package. It contains an XWidget version of Flutter's classic starter app. It only scratches the surface of XWidget's capabilities.

Please Note: The inflaters in the example were generated with Flutter 3.19, which means that if you're using an older version Flutter, you'll need to regenerate the inflaters using the following command:

$ dart run xwidget:generate --only inflaters

Here are some apps using XWidget:

Configuration #

By default, XWidget's code generator looks for a custom configuration file named xwidget_config.yaml in the project root. This custom configuration is layered on top of XWidget's own default configuration which handles most of the configuration burden. See package:xwidget/res/default_config.yaml for details.

Since the default config does most of the heavy lifting, the typical config can be relatively simple like this example:

# custom config - xwidget_config.yaml
inflaters:
  imports: [
    "dart:ui",
    "package:flutter/foundation.dart",
    "package:flutter/gestures.dart",
  ]
  sources: [ "lib/xwidget/inflater_spec.dart" ]
  includes: [ "lib/xwidget/inflater_spec_includes.dart" ]

icons:
  sources: [ "lib/xwidget/icon_spec.dart" ]

There are four top-level mappings that configure each of the four generated outputs: inflaters, schema, controllers, and icons.

Inflaters Configuration #

# Responsible for configuring inputs and outputs to generate inflaters.
inflaters:

  # The file path to save the generated code. The output contains all inflater classes
  # and a library function to to register them. The default value can be overwritten.
  # 
  # DEFAULT: "lib/xwidget/generated/inflaters.g.dart"
  target:

  # A list of additional imports to include in the generated output. Sometimes the code
  # generator can't determine all the required imports. This happens because of a
  # current limitation in dealing with default values for constructor arguments. This
  # option allows manual configuration when needed. Custom imports are appended to
  # XWidget's default list.
  #
  # DEFAULT: [ "package:xwidget/xwidget.dart" ]
  imports: [ ]

  # List of list inflater specification source files. Specifications tell XWidget which 
  # objects to create inflaters for.
  #
  # DEFAULT: none
  sources: [ ]

  # DEFAULT none
  includes: [ ]

  # DEFAULT: See 'package:xwidget/res/default_config.yaml'
  constructor_exclusions: [ "<class_name | * for any>:<constructor_argument_name>", ]

  # DEFAULT: See 'package:xwidget/res/default_config.yaml'
  constructor_arg_defaults:
    "<class_name | * for any>:<constructor_argument_name>": "<value>"

  # DEFAULT: See 'package:xwidget/res/default_config.yaml'
  constructor_arg_parsers:

    # EXAMPLES:
    # - "double": "double.parse(value)"
    # - "Alignment": "parseAlignment(value)"
    # - "*:width": "parseWidth(value)"
    "<constructor_argument_type | * for any>(: <constructor_argument_name>)": "<parser_function_call>"

// example inflater specification.
import 'package:flutter/material.dart';

// Best Practice: Keep declarations in alphabetical order. It makes it much easier
// to quickly determine what has been added and what is missing.

const inflaters = [
  AppBar,
  Center,
  Column,
  FloatingActionButton,
  Icon,
  MaterialApp,
  Scaffold,
  Text,
  TextStyle,
  ThemeData,
];

Schema Configuration #

# Responsible for configuring inputs and outputs to generate the inflater schema.
# Register the generated schema with your IDE to get code completion and documentation
# while editing fragments. 
schema:

  # DEFAULT: "xwidget_schema.g.xsd"
  target:

  # DEFAULT: "xwidget|res/schema_template.xsd"   
  template:

  # DEFAULT: See 'package:xwidget/res/default_config.yaml'
  types:
    # EXAMPLES
    # - "bool": "boolAttributeType"
    # - "BoxFit": "BoxFitAttributeType"
    "<constructor_argument_type>": "<schema_defined_type>"

  # DEFAULT: See 'package:xwidget/res/default_config.yaml'
  attribute_exclusions: [

    # EXAMPLES:
    # - "*:child"                       
    "<class_name | * for any>:<constructor_argument_name | * for any>",
  ]

Controllers Configuration #

controllers:

  # DEFAULT: "lib/xwidget/generated/controllers.g.dart" 
  target:

  # DEFAULT: [ "package:xwidget/xwidget.dart" ]
  imports: [ ]

  # DEFAULT: [ "lib/xwidget/controllers/**.dart" ]
  sources: [ ]

Icons Configuration #

icons:

  # DEFAULT: "lib/xwidget/generated/icons.g.dart"
  target:

  # DEFAULT: [ "package:xwidget/xwidget.dart" ]
  imports: [ ]

  # List of list icon specification source files. Specifications tell XWidget
  # which icons to register.
  #
  # DEFAULT: none
  sources: [ ]

// example icon specification
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';

// List icons individually to reduce app size.
const icons = [
  Icons.add,
  Icons.delete,
];

// Not recommended, but you can also include the entire icon set by simply
// referencing the enclosing class. This assumes that each icon is declared
// as a static field of type IconData.
const iconSets = [
  CupertinoIcons,
];

Code Generation #

Add documentation here.

$ dart run xwidget:generate 

$ dart run xwidget:generate --help 

$ dart run xwidget:generate --config "my_config.yaml" 

$ dart run xwidget:generate --only inflaters,controllers,icons 

$ dart run xwidget:generate --allow-deprecated

Inflaters #

Inflaters are the heart of XWidget. They are responsible for building the UI at runtime by parsing attribute values and constructing the components defined in fragments. In other words, they are the primary mechanism by which your XML markup gets transformed from this:

<Container height="50" width="50">
    <Text data="Hello world!"/>
</Container>

into the widget tree represented by this:

Container({
  height: 50,
  width: 50,
  child: Text("Hello world!")
});

A good analogy is the relationship between a recipe, a chef and a meal. The recipe describes how to create the meal. It lists the ingredients, preparation instructions, etc. The chef does all the work described in the recipe. The meal is the finished product. Your XML markup is the recipe, the inflaters are the chefs in the kitchen, and the instantiated widget tree is the meal, which is then served to the end user.

Inflaters are generated from a user (a developer using XWidget) defined specification written in Dart. The specification is very simple and its sole purpose is to tell the code generator which widgets to generate code for. Once the code has been generated, the widgets can be referenced in your markup.

You can create inflaters for basically anything that is a class and has a public constructor. For example, BoxDecoration and TextStyle are not widgets, they're helper classes that style widgets.

// a very simple inflater specification
import 'package:flutter/material.dart';

const inflaters = [
  Container,
  Text,
  TextStyle,
];

You can add as many components as required by your application; however, you should only specify components that you actually need. Specifying unused components in your configuration will unnecessarily increase your app size. This is because code is generated for every component you specify and thus neutralizes Flutter's tree-shaking.

There are four built-in inflaters: <Controller>, <DynamicBuilder>, <ListOf>, and ValueListener. You can read more about them in the [Custom Inflaters] section.

Parsers #

Each Inflater has a parseAttribute method that is responsible for parsing attribute values. The parsed values are then passed to the inflate method during object construction.

XWidget already knows how to parse most of the common attribute types such as bool, int, double, Alignment, Color, Curve, Duration, and many more. Please see default_config.yaml for a complete list. It's also capable of dynamically parsing any enum type without any additional configuration.

You can also create your own parsers, if XWidget's built-in capabilities are not enough. The built-in parsers are good examples of how to construct an attribute parser i.e. Alignment parser:

// Alignment parser
Alignment? parseAlignment(String? value) {
  if (value != null && value.isNotEmpty) {
    switch (value) {
      case 'topLeft': return Alignment.topLeft;
      case 'topCenter': return Alignment.topCenter;
      case 'topRight': return Alignment.topRight;
      case 'centerLeft': return Alignment.centerLeft;
      case 'center': return Alignment.center;
      case 'centerRight': return Alignment.centerRight;
      case 'bottomLeft': return Alignment.bottomLeft;
      case 'bottomCenter': return Alignment.bottomCenter;
      case 'bottomRight': return Alignment.bottomRight;
      default: throw Exception("Invalid alignment value: $value");
    }
  }
  return null;
}

Once you've created your parser, you'll need to register it inside your XWidget configuration file. Please see constructor_arg_parsers: under Inflaters Configuration for details.

Next, you'll need to make sure you import the dart file that contains your parser. Please see imports: under Inflaters Configuration for details.

XML Schema #

Add documentation here.

Code Completion & Tooltip Documentation #

Add documentation here.

Dependencies #

In the context of XWidget, dependencies are data, objects, and functions needed to render a fragment. The Dependencies object, at its core, is just a map of dependencies as defined above. Every inflate method call requires a Dependencies object. It can be a new instance or one that was received from a previous inflate method invocation.

Scoping #

copy #

inherit #

new #

Auto Scope #

Features #

Dependencies objects have a few characteristics that make them a little more interesting than plain old maps.

  1. Values can be referenced using dot/bracket notation for easy access to nested collections. Nulls are handled automatically. If the underlying collection does not exist, reads will resolve to null and writes will create the appropriate collections and store the data.

    Dart example:

    // example using setValue
final dependencies = Dependencies();
dependencies.setValue("users[0].name", "John Flutter");
dependencies.setValue("users[0].email", "name@example.com");
   
print(dependencies.getValue("users[0].name"));
print(dependencies.getValue("users[0].email"));

    Or you could use the constructor:

    // example setting values via Dependencies constructor
final dependencies = Dependencies({
  "users[0].name": "John Flutter",
  "users[0].email": "name@example.com"
});
   
print(dependencies.getValue("users[0].name"));
print(dependencies.getValue("users[0].email"));

    Markup usage example:

    <!-- example iterating over a collection -->
<forEach var="user" items="${users}">
  <Row>
    <Text data="${user.name}"/>
    <Text data="${user.email}"/>
  </Row>
</forEach>

  2. Supports global data. Sometimes you just need to access data from multiple parts of an application without a lot of fuss. Global data are accessible across all Dependencies instances by adding a global prefix to the key notation.

    Dart example:

    // example setting global values
final dependencies = Dependencies({
  "global.users[0].name": "John Flutter",
  "global.users[0].email": "name@example.com"
});
  
print(dependencies.getValue("global.users[0].name"));
print(dependencies.getValue("global.users[0].email"));

    Markup usage example:

    <!-- example iterating over a global collection -->
<forEach var="user" items="${global.users}">
  <Row>
    <Text data="${user.name}"/>
    <Text data="${user.email}"/>
  </Row>
</forEach>

  3. When combined with the ValueListener custom widget, the UI can listen for data changes and update itself. In the following example, if the user's email address changes, then the Text widget is rebuilt.

    <!-- example listening to value changes -->
<ValueListener varName="user.email">
    <Text data="${user.email}"/>
</ValueListener>

Note: Dependencies also supports the bracket operator []; however, it behaves like an ordinary map.

Model #

Add documentation here.

class Topic extends Model {

  // getters
  String get key => getValue("key!");
  String get label => getValue("label!");
  String get color => getValue("color!");
  String? get rank => getValue("rank");

  // setters
  set rank(String? rank) => setValue("rank", rank);

  Topic(super.data, {super.translation, super.immutable});
}

Null Safety #

Add documentation here.

! #

? #

Instance Management #

Add documentation here.

singleInstance #

Add documentation here.

class Topic extends Model {
  Topic._(super.data, {super.translation, super.immutable});

  factory Topic(
    Map<String, dynamic> data, {
    PropertyTranslation? translation,
    bool? immutable,
  }) {
    return Model.singleInstance<Topic>(
      factory: Topic._,
      data: data,
      tranlsation: translation,
      immutable: immutable
    );
  }
}

keyedInstance #

Add documentation here.

XWidget.registerModel<Topic>(Topic.new, const [
  PropertyTransformer<String>("key", isKey: true),
  PropertyTransformer<String?>("name"),
]);

class Topic extends Model {
  Topic._(super.data, {super.translation, super.immutable});

  factory Topic(
    Map<String, dynamic> data, {
    PropertyTranslation? translation,
    bool? immutable,
  }) {
    return Model.keyedInstance<Topic>(
      factory: Topic._,
      data: data,
      tranlsation: translation,
      immutable: immutable
    );
  }
}

hasInstance #

Add documentation here.

clearInstances #

Add documentation here.

Loading Data #

When loading data into your models, you may need to first transform its structure or convert its properties to different types. To do this, use PropertyTransformer and PropertyTranslation classes to define the target format and data mappings.

PropertyTransformer #

Each PropertyTransformer instance represents a property in your model. It describes a property's name, data type, and default value. They define the structure of your model. When you register a model using XWidget.registerModel() you can optionally pass a list of PropertyTransformers. These transformers will automatically be used whenever you create a new model instance.

// register Content model class
XWidget.registerModel<Content>(Content.new, const [
  PropertyTransformer<String>("title"),
  PropertyTransformer<String?>("summary"),
  PropertyTransformer<List<Image>>("images"),
]);

// register Image model class
XWidget.registerModel<Image>(Image.new, const [
    PropertyTransformer<String>("url"),
    PropertyTransformer<String?>("caption"),
    PropertyTransformer<bool>("active", defaultValue: true),
]);

class Content extends Model {
  Content(super.data, {super.translation, super.immutable}); 
}

class Image extends Model {
  Image(super.data, {super.translation, super.immutable});
}

The following property types are natively supported:

  • Anything that extends Model, provided it's registered using with XWidget.registerModel().
  • The Basic types String, int, double, and bool.
  • The types Color, DateTime, and Duration.
  • The collections List, Set and Map. Prefer using a subclass of Model class over Map, if possible.
  • List<List> is not well supported at the moment
  • Custom types are supported by registering transform functions. See Transform Functions

PropertyTranslation #

The PropertyTranslation class enables you to map a source data structure to a target data structure, making it particularly useful when the source data structure doesn't align with your model's structure. This class is also beneficial when your model needs to load data from various sources, each with its own distinct data structure. Simply specify a source/target property pair for each property that needs to be mapped. If a target property is not explicitly mapped, it will default to using the same name for the source property.

// translate 'firstName' to 'first' and 'lastName' to 'last' translation. Since all other source
// property names match the target property names, they will be imported without translation.

XWidget.registerModel<Person>(Person.new, const [
  PropertyTransformer<String>("first"),
  PropertyTransformer<String>("last"),
  PropertyTransformer<bool>("employee"),
  PropertyTransformer<int>("age"),
]);

class Person extends Model {
  Person(super.data, {super.translation, super.immutable});
}

final person = Person({
  "firstName": "Mike",
  "lastName": "Jones",
  "employee": "true",
  "age": "25"
}, translation: PropertyTranslation({
  "firstName": "first",
  "lastName": "last"
}));

expect(person, {
  "first": "Mike",
  "last": "Jones",
  "employee": true,
  "age": 25
});

// this example shows how to load data into a nested model, 'Image'.

XWidget.registerModel<Content>(Content.new, const [
  PropertyTransformer<String>("title"),
  PropertyTransformer<String?>("summary"),
  PropertyTransformer<Image>("image"),
]);

XWidget.registerModel<Image>(Image.new, const [
  PropertyTransformer<String>("url"),
  PropertyTransformer<String?>("caption"),
]);

class Content extends Model {
  Content(super.data, {super.translation, super.immutable});
}

class Image extends Model {
  Image(super.data, {super.translation, super.immutable});
}

final content = Content({
  "title": "Hello World",
  "summary": "Basic App",
  "imageUrl": "https://www.example.com/image.jpg",
  "imageCaption": "Sunset",
}, translation: PropertyTranslation({
  "imageUrl": "image.url",
  "imageCaption": "image.caption",
}));

expect(content, {
  'title': 'Hello World',
  'summary': 'Basic App',
  'image': {'url': 'https://www.example.com/image.jpg', 'caption': 'Sunset'}
});

// this example shows how to add multiple models to a List.

XWidget.registerModel<Content>(Content.new, const [
  PropertyTransformer<String>("title"),
  PropertyTransformer<String?>("summary"),
  PropertyTransformer<List<Image>>("images"),
]);

XWidget.registerModel<Image>(Image.new, const [
  PropertyTransformer<String>("url"),
  PropertyTransformer<String?>("caption"),
]);

class Content extends Model {
  Content(super.data, {super.translation, super.immutable});
}

class Image extends Model {
  Image(super.data, {super.translation, super.immutable});
}

final content = Content({
  "title": "Hello World",
  "summary": "Basic App",
  "myImages": [
    {"url": "https://www.example.com/image1.jpg", "caption": "#1"},
    {"url": "https://www.example.com/image2.jpg", "caption": "#2"},
    {"url": "https://www.example.com/image3.jpg", "caption": "#3"},
  ]
}, translation: PropertyTranslation({
  "myImages": "images",
}));

expect(content, {
  'title': 'Hello World',
  'summary': 'Basic App',
  'images': [
    {'url': 'https://www.example.com/image1.jpg', 'caption': '#1'},
    {'url': 'https://www.example.com/image2.jpg', 'caption': '#2'},
    {"url": "https://www.example.com/image3.jpg", "caption": "#3"},
  ]
});

// this example shows how to add multiple unindexed models to a list.

XWidget.registerModel<Content>(Content.new, const [
  PropertyTransformer<String>("title"),
  PropertyTransformer<String?>("summary"),
  PropertyTransformer<List<Image>>("images"),
]);

XWidget.registerModel<Image>(Image.new, const [
  PropertyTransformer<String>("url"),
  PropertyTransformer<String?>("caption"),
]);

class Content extends Model {
  Content(super.data, {super.translation, super.immutable});
}

class Image extends Model {
  Image(super.data, {super.translation, super.immutable});
}

final model = TestModel({
  "title": "Hello World",
  "summary": "Basic App",
  "primaryImageUrl": "https://www.example.com/image.jpg",
  "secondaryImageUrl": "https://www.example.com/image2.jpg",
  "secondaryImageCaption": "Secondary",
}, translation: PropertyTranslation({
  "primaryImageUrl": "images.url",
  "primaryImageCaption": "images.caption",
  "secondaryImageUrl": "images.url",
  "secondaryImageCaption": "images.caption",
}));

expect(model, {
  'title': 'Hello World',
  'summary': 'Basic App',
  'images': [
    {'url': 'https://www.example.com/image.jpg'},
    {'url': 'https://www.example.com/image2.jpg', 'caption': 'Secondary'}
  ]
});

Type Converters #

When importing model data, XWidget converts source data types into the target's data types using converter functions. There are preregistered converter functions for String, int, double, bool, DateTime, Duration, Color and dynamic. You can also define custom type converters using the XWidget.registerTypeConverter method. Typically, you should registration your custom functions in main().

main() {
  XWidget.registerTypeConverter<Money>((value) {
    if (value is Money) {
      return value;
    } else if (value is String) {
      return Money.parse(value, isoCode: 'USD');
    } else if (value is int) {
      return Money.fromInt(value, isoCode: 'USD');
    } else {
      throw Exception("Unable to convert value of type ${value.runtimeType} to 'Money'");
    }
  });
}

Fragments #

Add documentation here.

Controllers #

Add documentation here.

Expression Language (EL) #

Add documentation here.

Operators #

Below is the operator precedence and associativity table. Operators are executed according to their precedence level. If two operators share an operand, the operator with higher precedence will be executed first. If the operators have the same precedence level, it depends on the associativity. Both the precedence level and associativity can be seen in the table below.

Level Operator Category Associativity
10 ()
[]
.		 Function call, scope, array/member access
9 -expr
!expr		 Unary Prefix
8 *
/
~/
%		 Multiplicative Left-to-right
7 +
-		 Additive Left-to-right
6 <
>
<=
>=		 Relational
5 ==
!=		 Equality
4 && Logical AND Left-to-right
3 || Logical OR Left-to-right
2 expr1 ?? expr2 If null Left-to-right
1 expr ? expr1 : expr2 Conditional (ternary) Right-to-left

Static Functions #

These functions are universally accessible within every EL (Expression Language) expression, providing powerful tools for manipulation and evaluation. They are designed to accept other expressions as arguments, enabling dynamic and flexible computation. This allows for the creation of complex expressions by combining multiple functions and expressions, enhancing the overall functionality and usability of EL in various contexts.

List of static functions:

num abs(dynamic value);
int ceil(dynamic value);
bool contains(dynamic value, dynamic searchValue);
bool containsKey(Map? map, dynamic searchKey);
bool containsValue(Map? map, dynamic searchValue);
Duration diffDateTime(DateTime left, DateTime right);
bool endsWith(String value, String searchValue);
dynamic eval(String? value);
dynamic first(dynamic value);
int floor(dynamic value);
String formatDateTime(String format, DateTime dateTime);
String? formatDuration(Duration? value, [String precision = "s", DurationFormat? format = defaultDurationFormat]);
bool isBlank(dynamic value);
bool isEmpty(dynamic value);
bool isFalseOrNull(dynamic value);
bool isNotBlank(dynamic value);
bool isNotEmpty(dynamic value);
bool isNotNull(dynamic value);
bool isNull(dynamic value);
bool isTrueOrNull(dynamic value);
dynamic last(dynamic value);
int length(dynamic value);
void logDebug(dynamic message);
bool matches(String value, String regExp);
DateTime now();
DateTime nowInUtc();
double randomDouble();
int randomInt(int max);
String replaceAll(String value, String regex, String replacement);
String replaceFirst(String value, String regex, String replacement, [int startIndex = 0]);
int round(dynamic value);
bool startsWith(String value, String searchValue);
String substring(String value, int start, [int end = -1]);
bool? toBool(dynamic value);
Color? toColor(dynamic value);
DateTime? toDateTime(dynamic value);
int? toDays(dynamic value);
double? toDouble(dynamic value);
Duration? toDuration(dynamic value, [String? intUnit]);
int? toHours(dynamic value);
int? toInt(dynamic value);
int? toMillis(dynamic value);
int? toMinutes(dynamic value);
int? toSeconds(dynamic value);
String? toString(dynamic value);
bool tryToBool(dynamic value);
Color? tryToColor(dynamic value);
DateTime? tryToDateTime(dynamic value);
int? tryToDays(dynamic value);
double? tryToDouble(dynamic value);
Duration? tryToDuration(dynamic value, [String? intUnit]);
int? tryToHours(dynamic value);
int? tryToInt(dynamic value);
int? tryToMillis(dynamic value);
int? tryToMinutes(dynamic value);
int? tryToSeconds(dynamic value);
String? tryToString(dynamic value);

Some examples:

// Absolute Value
${abs(-42)}  // Returns 42

// Rounding a Number
${round(3.7)}  // Returns 4

// Checking if a String Contains a Substring
${contains('Hello, World!', 'World')}  // Returns true

// Getting Current Date and Time
${now()}  // Returns the current date and time

// Formatting a Date
${formatDateTime('yyyy-MM-dd', now())}  // Returns current date in YYYY-MM-DD format

// Checking if a Collection is Empty
${isEmpty(myList)}  // Returns true if myList is empty

// Generating a Random Integer
${randomInt(100)}  // Returns a random integer between 0 and 99

// Replacing a Substring
${replaceAll('I love programming', 'love', 'enjoy')}  // Returns 'I enjoy programming'

// Checking if a String Starts With a Substring
${startsWith('Dart is fun', 'Dart')}  // Returns true

// Converting to Integer
${toInt('123')}  // Returns 123

// Getting the Length of a String
${length('Hello')}  // Returns 5

// Evaluating an Expression
${eval('2 + 2')}  // Returns 4

Instance Functions #

In addition to using static functions, you can call instance functions on references and expressions. This allows you to access and manipulate their properties dynamically. Instance functions operate on specific instances of a class and can provide more tailored behavior based on the object's state.

Please note that not all instance functions are supported. If you attempt to call a function that does not exist on an object, a NoSuchMethodError will be thrown. To help you navigate this limitation, below is a curated list of supported instance functions:

// alphabetical order
T abs();
int ceil();
int compareTo(T other);
bool contains(E element);
bool containsKey(K key);
bool containsValue(V value);
Set<E> difference(Set<Object> other);
E elementAt(int index);
bool endsWith(String other);
Iterable<MapEntry<K, V>> entries;
E first();
int floor();
int indexOf(E element, [int start = 0]);
Set<E> intersection(Set<Object> other);
bool isEmpty();
bool isEven();
bool isFinite();
bool isInfinite();
bool isNaN();
bool isNegative();
bool isNotEmpty();
bool isOdd();
Iterable<K> keys();
E last();
int lastIndexOf(E element, [int start]);
int length();
Iterable<RegExpMatch> matches(String input);
String padLeft(int width, [String padding = ' ']);
String padRight(int width, [String padding = ' ']);
String replaceAll(Pattern from, String replace);
String replaceFirst(Pattern from, String replace, [int startIndex = 0]);
String replaceRange(int start, int end, String replacement);
int round();
Type runtimeType();
void shuffle([Random? random]);
E single();
List<String> split(Pattern pattern);
bool startsWith(String other, [int index = 0]);
List<E> sublist(int start, [int? end]);
String substring(int start, [int? end]);
double toDouble();
int toInt();
List<E> toList({bool growable = true});
String toLowerCase();
String toRadixString(int radix);
Set<E> toSet();
String toString();
String toUpperCase();
String trim();
String trimLeft();
String trimRight();
int truncate();
Set<E> union(Set<E> other);
Iterable<V> values();

Some examples:

// List Operations
${myList.length()}  // Returns the number of elements in myList

// Map Access
${myMap.containsKey('key1')}  // Checks if 'key1' exists in myMap

// String Manipulation
${(person.firstName + ' ' + person.lastName).toUpperCase()} // Converts expression to uppercase

Custom Functions #

Custom functions are user-defined functions that you can add to any Dependencies instance. While they behave similarly to static functions, they are specifically bound to a single Dependencies instance.

It's important to note that custom functions can only accept positional arguments, which means they cannot use named parameters.

For example:

// Define a custom function
void greet(String name) {
  return 'Hello, $name!';
}

// Add the custom function to the Dependencies instance
dependencies.setValue("greet", greet);

// Call 'greet' custom function
${greet('Sally')} // Returns: Hello, Sally!

Resources #

Add documentation here.

Strings #

Add documentation here.

Integers #

Add documentation here.

Doubles #

Add documentation here.

Booleans #

Add documentation here.

Colors #

Add documentation here.

Fragments #

Add documentation here.

Components #

Add documentation here.

Flutter #

Add documentation here.

Third Party #

Add documentation here.

Built-In #

Add documentation here.

<Controller> #

Add documentation here.

<DynamicBuilder> #

Add documentation here.

<EventListener> #

Add documentation here.

<List> #

Add documentation here.

<Map> #

Add documentation here.

<MapEntry> #

Add documentation here.

<MediaQuery> #

Add documentation here.

<ValueListener> #

Add documentation here.

Custom #

Add documentation here.

Tags #

Tags are XML elements that do not, themselves, add components to the widget tree. They provide common structure and control elements for constructing the UI such as conditionals, iteration, fragment inclusion, etc. They are always represented in lowercase to distinguish them from inflaters.

<builder> #

A tag that wraps its children in a builder function.

This tag is extremely useful when the parent requires a builder function, such as PageView.builder. Use vars, multiChild, and nullable attributes to define the builder function signature. When the builder function executes, the values of named arguments defined in vars are stored as dependencies in the current Dependencies instance. The values of placeholder arguments (_) are simply ignored. The BuildContext is never stored as a dependency, even if explicitly named, because it would cause a memory leak.

Attribute Description Required Default
dependenciesScope Defines the method for passing Dependencies to immediate children. Valid values are new, copy, and inherit. no auto
for The name of the parent's attribute that will be assigned the builder function. yes null
multiChild Whether the builder function should return an array of widgets or a single widget. no false
nullable Whether the builder function can return null. no false
vars A comma separated list of builder function arguments. Values of named arguments are stored as dependencies. Supports up to five arguments. no null

Example usage:

<PageView.builder>
    <builder for="itemBuilder" vars="_,index" nullable="true">
        <Container>
            <Text data="${index}"/>
        </Container>
    </builder>
</PageView.builder>

<callback> #

This tag allows you to bind an event handler with custom arguments. If you don't need to pass any arguments, then just bind the handler using EL, like so: <TextButton onPressed="${onPressed}"/>. This is sufficient in most cases.

The callback tag creates an event handler function for you and executes the action when the event is triggered. action is an EL expression that is evaluated at the time of the event. Do not enclose the expression in curly braces ${...}, otherwise it will be evaluated immediately upon creation instead of when the event is fired.

If the handler function defines arguments in its signature, you must declare those arguments using the vars attribute. This attribute takes a comma separated list of argument names. When the handler is triggered, argument values are added to Dependencies using the specified name as the key, and can be referenced in the action EL expression, if needed. They're also accessible anywhere else that instance of Dependencies is available. If you don't need the values, then use and underscore (_) in place of the name. Doing so will ignore the values and they won't be added to Dependencies e.g. ...vars="_,index".... BuildContext is never added to Dependencies even when named, because this would cause a memory leak.

Attribute Description Required Default
action The El expression to evaluate when the event handler is triggered. yes null
dependenciesScope Defines the method for passing Dependencies to immediate children. Valid values are new, copy, and inherit. no auto
for The name of the parent's attribute that will be assigned the event handler. yes null
returnVar The storage destination within Dependencies for the return value of action. no null
vars A comma separated list of handler function arguments. Values of named arguments are stored as dependencies. Supports up to five arguments. no null 
<TextButton>
    <callback for="onPressed" action="doSomething('Hello World')"/>
    <Text>Press Me</Text>
</TextButton>

<debug> #

A simple tag that logs a debug message

Attribute Description Required Default
message The message to log. yes null 
<debug message="Hello world!"/>

<forEach> #

Add documentation here.

Attribute Description Required Default
dependenciesScope Defines the method for passing Dependencies to immediate children. Valid values are new, copy, and inherit. no copy
indexVar no null
items yes null
multiChild no null
nullable no null
var yes null 
<forEach var="user" items="${users}">

</forEach>

<forLoop> #

Add documentation here.

Attribute Description Required Default
begin no 0
dependenciesScope Defines the method for passing Dependencies to immediate children. Valid values are new, copy, and inherit. no copy
end no 0
step no 1
var yes null 
<forLoop var="index" begin="1" end="5">

</forLoop>

<fragment> #

A tag that renders a UI fragment

Attribute Description Required Default
dependenciesScope Defines the method for passing Dependencies to immediate children. Valid values are new, copy, and inherit. no auto
for The name of the parent's attribute that will be assigned the fragment's output. no null
name The Resources name of the fragment. yes null 
<AppBar>
    <fragment for="leading" name="profile/icon"/>
</AppBar>

<if>/<else> #

Add documentation here.

Attribute Description Required Default
test EL expression tht must evaluate to a bool value. yes null 
<if test="${}">
    <fragnent name=""/>
    <else>
        <fragnent name=""/>
    </else>
</if>

<var> #

Add documentation here.

Attribute Description Required Default
name yes null
value yes null 
<var name="" value=""/>

Best Practices #

Do use fragment folders #

Add documentation here.

Don't specify unused widgets #

Add documentation here.

Do check-in generated files into source control #

Add documentation here.

Instantiate a new Dependencies object for each page #

    Navigator.of(context).push(MaterialPageRoute(builder: (context) {
      return Scaffold(
          body: XWidget.inflateFragment("profile/settings", Dependencies())
      );
    }));

Add documentation here.

Prefer automatic scoping of Dependencies #

Add documentation here.

Do extend Model and create constructors with explicit properties #

While it's convenient to use the Model class as-is, extending the Model class and creating a constructor with all your model's properties defined as parameters is a more robust approach. This method ensures that all data is validated before it enters your model, helping prevent errors down the road.

// easy, but error prone
final profile = Model({
  "username": "mike.smith",
  "email": "mike.smith@example.com",
  "name": "Mike Smith"
});

// more verbose, but more stable and fewer potential errors
final profile = Profile(
  username: "mike.smith",
  email: "mike.smith@example.com",
  name: "Mike Smith"
);

class Profile extends Model {
  String get username => getValue("username");
  String get email => getValue("email");
  String? get name => getValue("name");
  DateTime? get lastLogin => getValue("lastLogin");
  
  Profile({
    required String username,
    required String email,
    String? name,
    DateTime? lastLogin,
  }) :super({
    "username": username,
    "email": email,
    "name": name,
    "lastLogin": lastLogin,
  });
}

If you need to load data from a Map structure, then override propertyTransformers getter and add an import factory constructor. See Model -> Loading Data for more information.

Note: In the near future, XWidget will have the ability to generate most of the required code for you.

XWidget.registerModel<Profile>(Profile.import, const [
    PropertyTransformer<String>("username"),
    PropertyTransformer<String>("email"),
    PropertyTransformer<String?>("name"),
    PropertyTransformer<DateTime?>("lastLogin"),
]);

class Profile extends Model {
  String get username => getValue("username");
  String get email => getValue("email");
  String? get name => getValue("name");
  DateTime? get lastLogin => getValue("lastLogin");
  
  Profile({
    required String username,
    required String email,
    String? name,
    DateTime? lastLogin,
  }) :super({
    "username": username,
    "email": email,
    "name": name,
    "lastLogin": lastLogin,
  });

  Profile.import(super.data, {super.translation, super.immutable});
}

Add documentation here.

project
├── lib
│   └── xwidget          # holds all specification files used in code generation
│       ├── controllers  # holds all custom controllers
│       └── generated    # holds all generated .g.dart files
└── resources
    ├── fragments  # holds all fragments
    └── values     # holds all resource values i.e strings.xml, bools.xml, colors.xml, etc.

Tips and Tricks #

Regenerate inflaters after upgrading Flutter #

Add documentation here.

Use controllers to create reusable components #

Add documentation here.

Specify generic types with literals when your model is mutable. #

When listening for changes using <ValueListener> or listenForChanges, XWidget wraps a ModelValueNotifier around the data that is being listening to. Therefore, it is important that model collections be type agnostic i.e. dynamic or Object?. For example:

// don't do this - no types
final model = Model({
  "users": {
    "user1": { "email": "@", "phone": "0" },
    "user2": { "email": "@", "phone": "0" }
  }
});
// throws exception
final user1Notifier = model.listenForChanges("users.user1", null, null);

This throws type 'ModelValueNotifier' is not a subtype of type 'Map<String, String>' of 'value'. To fix this, explicitly specify the Map's key and value types:

// this is ok - explicitly typed maps
final model = Model({
  "users": <String, dynamic>{
    "user1": <String, dynamic>{ "email": "@", "phone": "0" },
    "user2": <String, dynamic>{ "email": "@", "phone": "0" }
  }
});
// this now works.
// NOTE: You typically wouldn't call `listenForChanges' directly. You would use
// <ValueListener> in your fragment instead.
final user1Notifier = model.listenForChanges("users.user1", null, null);

Trouble Shooting #

The generated inflater code has errors #

The most common cause of errors in generated inflater code is due to constructor argument defaults referencing undefined variables. If the referenced variable type is not a primitive, then XWidget can't infer how to generate the default value and will fallback to using the variable reference.

The solution is to manually set the default value for the constructor argument in XWidget's configuration file under the constructor_arg_defaults: key.

# xwidget_config.yaml
inflaters:  
  constructor_arg_defaults:
    # example defaults
    "WidgetSpan:alignment": "PlaceholderAlignment.middle",
    "*:colorBlendMode": "BlendMode.srcIn"

See Inflaters Configuration for details.

Hot Reload/Restart clears dependency values #

Hot reload loads code changes into the VM and re-builds the widget tree, preserving the app state; it doesn't rerun main() or initState().

Make sure that you're not binding dependencies in main(), initState() or any other initialization function such as Controller.initialize(). Dependencies should be bound in the build function of your widget. If you are using a Controller, simply override the bindDependencies() method with your implementation and XWidget will handle the rest.

FAQ #

1. What problems does XWidget solve? #

The first and most obvious answer is that it gives applications the flexibility to create and modify its UI at runtime. An app might want to give its users the ability to download a different look-and-feel or create dynamic forms all without a redeployment. You're only limited by the existing functionality of your custom controllers, since they're static Dart code.

It provides better separation between business and presentation layers out of the box. Sometimes developers struggle with the best way to separate these concerns. XWidget inherently addresses these problems in an uncomplicated way with fragments and controllers.

This may just be our opinion, but building views in code just feels clunky. We find it more enjoyable to write our UIs using markup - it feels more natural and it's certainly a lot easier to read. The experience should only get better as we improve IDE integration.

I don't need dynamic UIs, why should I still use XWidget? #

While not all apps require dynamic user interfaces, incorporating XWidget can still yield substantial benefits. XWidget enhances code quality by promoting organization and readability, contributing to overall code improvement.

Code readability is a fundamental aspect of quality code for any software project. Readable code is much easier to debug, maintain, and understand. XWidget's strong separation between presentation logic and layout leads to better organized code. Its XML based markup language for building layouts is vastly easier to read and modify than the default, code centric approach offered by the Flutter framework. Additionally, XWidget can manage your static string, boolean, numeric, and color resources, so that values are never hardcoded directly into your layouts or anywhere else. Please read the Fragments, Controllers, and Resources sections above.

Roadmap #

The primary focus right now is documentation, critical bug fixes, more documentation, minor improvements, and oh, even more documentation. The implementation is already fairly stable, but lacks test coverage. Once the documentation is complete, we'll bump the minor version and concentrate on testing.

0.0.x Releases (2023) #

  • Write README and API documentation
  • Critical bug fixes
  • Minor improvements

0.x Releases (2024) #

  • Write unit, widget, UI, and performance tests
  • Critical and major bug fixes
  • Refine and add documentation as needed

1.0.0 Release (mid 2024) #

  • Stable release

Known Issues #

None at the moment 😄

← Metadata

15
likes
140
points
100
downloads

Publisher

verified publisherappfluent.us

Weekly Downloads

Metadata

A package for building dynamic UIs in Flutter using an expressive, XML based markup language.

Repository (GitHub)
View/report issues

Topics

#dynamic #layout #ui #widget #xml

Documentation

API reference

License

MIT (license)

Dependencies

analyzer, args, flutter, glob, intl, logger, markdown, path, petitparser, type_plus, xml, yaml

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