json_dynamic_widget 4.0.0-beta+1 
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peifferinnovations.comA library to dynamically generate widgets within Flutter from JSON or other Map-like structures.
json_dynamic_widget #
Table of Contents #
- Live Example
- First Party Plugins
- Migration to 4.X.X version
- Introduction
- Understanding the Registry
- Built In Widgets
- Using Expressions
- Creating Custom Widgets
- Creating Custom Arg Processor
Live Example #
First Party Plugins #
Here's a list of first party plugins that exist for this library.
- json_dynamic_widget_plugin_charts_flutter
- json_dynamic_widget_plugin_font_awesome
- json_dynamic_widget_plugin_ionicons
- json_dynamic_widget_plugin_lottie
- json_dynamic_widget_plugin_material_icons
- json_dynamic_widget_plugin_markdown
- json_dynamic_widget_plugin_rive
- json_dynamic_widget_plugin_svg
Migration to 4.X.X version #
With 4.0.0 version the new syntax has been introduced for JSONs. The way of expressing variables and functions has been change. Total table of change and the way how to migrate the JSON definitions to support new format.
| The change | Previous | New |
|---|---|---|
| Variables syntax | {{varName}} |
${varName} |
| Function syntax | ##func1(string,{{varName}})## |
${func1('string', varName)} |
| Lack of static variables | !{{staticVarName}} |
All listen variables can be defined as "listen":["var1","var2"] in JSON. Lack of the staticVarName in such an array is equivalent of static variable in the previous syntax |
| Removed JsonPath from variables | {{dynamic;$.person.firstName}} |
${dynamic['person']['firstName']} |
Removed NamedFunctionArg |
##myFunction(key:keyName, value:{{value}})## |
${myFunction({"key":'keyName','value':value})} |
| Escaping of commas is not needed in function params | ##sayHello(Hello\\, {{firstName}}!)## |
${sayHello('Hello, '+ firstName)} |
Introduction #
Important Note: Because this library allows for dynamic building of Icons, Flutter's built in tree shaker for icons no longer has the ability to guarantee what icons are referenced vs not. Once you include this as a dependency, you must add the --no-tree-shake-icons as a build flag or your builds will fail.
Example:
flutter build [apk | web | ios | ...] --no-tree-shake-icons
This library provides Widgets that are capable of building themselves from JSON structures. The general structure follows:
{
"type": "<lower_case_type>",
"args": {
"...": "..."
},
"child": {
"...": "..."
},
"children": [{
"...": "...",
}],
"listen": []
}
Where the child and children are mutually exclusive. From a purely technical standpoint, there's no difference between passing in a child or a children with exactly one element.
The listen array is used to define variable names that specified JsonWidgetData listen to. Thanks to that JsonWidgetData will be rebuilt with every change of such a variables.
In case of not defining such a array the JsonWidgetRegistry will try to built such a array dynamically and use any met variable. Good practice is to define it by a hand to reduce amount of rebuilds.
See the documentation and / or example app for the currently supported widgets. All built types are encoded using a lower-case and underscore separator as opposed to a camel case strategy. For instance, a ClipRect will have a type of clip_rect.
Once you have the JSON for a widget, you will use the JsonWidgetData to build the resulting Widget that can be added to the tree. For performance reasons, the JsonWidgetData should be instantiated once and then cached rather than created in each build cycle.
Example
import 'package:flutter/material.dart';
import 'package:json_dynamic_widget/json_dynamic_widget.dart';
class MyStatefulWidget extends StatefulWidget {
MyStatefulWidget({
@required this.jsonData,
this.registry,
Key key,
}): assert(jsonData != null),
super(key: key)
final Map<String, dynamic> jsonData;
final JsonWidgetRegistry registry;
@override
_MyWidgetState createState() => _MyWidgetState();
}
class _MyWidgetState extends State<MyStatefulWidget> {
@override
void initState() {
super.initState();
_data = JsonWidgetData.fromDynamic(widget.jsonData);
}
@override
Wiget build(BuildContext context) => _data.build(
context,
registry: widget.registry ?? JsonWidgetRegistry.instance,
);
}
Understanding the Registry #
The JsonWidgetRegistry is the centralized processing warehouse for building and using the JSON Dynamic Widgets. Widgets must be registered to the registry to be available for building. The registry also supports providing dynamic variables and dynamic functions to the widgets that it builds.
The Registry is also repsonsible for processing JsonWidgetData args to their
real values via arg processors. Users can define their own arg processors which is giving the possibility to define the custom syntax.
When a value changes on the registry, it posts a notification to the valueStream so any potential processing logic can be executed. The dynamic widgets that use variable values also listen to this stream so they can update their widget state when a value they use for rendering change.
The registry always has a default instance that will be used when a substitute registry is not given. Substitute registeries can be created and used to isolate variables and functions within the app as needed. For instance, you may want a separate registry per page if each page may set dynamic values on the registry. This can prevent the values from one page being overwritten by another.
Built In Widgets #
The structure for all the args is defined in each widget builder, which are defined below:
Using Expressions #
The library since version 4.0.0 has a tight integration with expressions library. By integrating the JsonWidgetRegistry variables and functions with that library there is possible to define different kind of simple expressions placed between ${}.
Using Variables #
Variables can be defined on the JsonWidgetRegistry that is used to render the dynamic widgets.
A variable can be used in any of the child / children / args values and for certain types of properties, a variable reference if the only way to actually assign that value.
Widgets that accept user input will assign that user input to a variable named the value inside of the id option, if an id exists. This allows widgets the ability to listen to input value updates.
There is a possibility to use them in JSON definition thanks to expressions library. Few examples:
${dynamicVariable}
${dynamic['persons'][0]}
${'Hello ' + name}
More examples is available at variables.json.
The built in variables are defined below:
| Variable Name | Example | Description |
|---|---|---|
${curveName}_curve |
|
Provides a const instance of any of the Curves const values. The name of the Curve constant should be transformed into snake_case. |
Dynamic Functions #
Basic function usage
Like any other expression functions defined in JsonWidgetRegistry can be used in JSON by placing their name and params between ${}. For example:
${sayHello('Hello,' + firstName)}
Assuming the function sayHello is implemented as, and the firstName variable is "Ted":
print(args[0]);
... then the output of that could would be:
Hello, Ted!
Named args in functions
Additionally we can pass a map to the function:
${myFunction({'key':'keyName', 'value':value})}
Now, in your function, the args will be passed as such:
[
{"key":"keyName", "value": <<value of the variable from the registry>>}
]
This allows function that take multiple, optional, values to be more easily created and called vs having to do something like...
${myFunction(value, null, null, null, '#ff0000')}
Complex function calls
This is possible to construct really complex function calls:
${func1(func2(func3()+' text'+var1), func4(1+2))}
Built functions
The built in functions are defined below:
| Function Name | Example | Args | Description |
|---|---|---|---|
dynamic |
${dynamic('operationVar1', 'operationVar2'...)} |
The variable names which contains values convertable into DynamicOperation. |
Executes every DynamicOperation passed as args. |
for_each |
${for_each(items['data']['items'], 'templateName', 'value', 'key')} |
|
Iterates over the list or map defined by the first arg and builds the widget defined in the template / second argument. The value will be placed in either the variable named value or the passed in third argument. Finally, the index or key will be placed in key or the fourth arg's name. |
length |
${length(myVar)} |
|
Returns the length of the first argument. If the argument is a JSON encoded String, this will first decode it to the native representation. Next, the return value depends on the type of argument. If the arg is a String, a Map, a List, a Set, or an Iterable, the result of calling .length on it will be returned. Otherwise if the arg is an int or a double, the int value of the arg will be returned. Other types will result in an exception. |
log |
${log('my message', 'info')} |
|
Logs the given message out to the logger using the optional level or finest if not set. |
navigate_named |
${navigate_named('home', someValue)} |
|
Navigates to the named route. The GlobalKey<NavigatorState> must be provided to the registry before this will work. |
navigate_pop |
${navigate_pop(false)} |
|
Pop's the navigator stack. The GlobalKey<NavigatorState> must be provided to the registry before this will work. |
noop |
${noop()} |
n/a | Simple no-arg no-op function that can be used to enable buttons for UI testing. |
remove_value |
${remove_value('varName')} |
|
Removes the variable named in the first argument from the registry. |
set_value |
${set_value('varName', 'some value')} |
|
Sets the value of the variable in the registry. |
Creating Custom Widgets #
Creating a custom widget requires first creating a JsonWidgetBuilder for the widget you would like to add.
For example, if you would like to create a new widget that can render a SVG, you would create a SvgWidgetBuilder like the following:
import 'package:child_builder/child_builder.dart';
import 'package:flutter/material.dart';
import 'package:json_class/json_class.dart';
import 'package:json_dynamic_widget/json_dynamic_widget.dart';
import 'package:json_theme/json_theme.dart';
import 'package:meta/meta.dart';
import 'package:websafe_svg/websafe_svg.dart';
class SvgBuilder extends JsonWidgetBuilder {
SvgBuilder({
this.asset,
this.color,
this.height,
this.url,
this.width,
}) : assert(asset == null || url == null),
assert(asset != null || url != null);
static const type = 'svg';
final String asset;
final Color color;
final double height;
final String url;
final double width;
static SvgBuilder fromDynamic(
dynamic map, {
JsonWidgetRegistry registry,
}) {
SvgBuilder result;
if (map != null) {
result = SvgBuilder(
asset: map['asset'],
color: ThemeDecoder.decodeColor(
map['color'],
validate: false,
),
height: JsonClass.parseDouble(map['height']),
url: map['url'],
width: JsonClass.parseDouble(map['width']),
);
}
return result;
}
@override
Widget buildCustom({
ChildWidgetBuilder childBuilder,
@required BuildContext context,
@required JsonWidgetData data,
Key key,
}) {
assert(
data.children?.isNotEmpty != true,
'[SvgBuilder] does not support children.',
);
return asset != null
? WebsafeSvg.asset(
asset,
color: color,
height: height,
width: width,
)
: WebsafeSvg.network(
url,
color: color,
height: height,
width: width,
);
}
}
Widget builders can also have well defined JSON schemas associated to them. If a widget builder has an associated JSON schema then in DEBUG modes, the JSON for the widget will be processed through the schema validator before attempting to build the widget. This can assist with debugging by catching JSON errors early.
An example schema for the SvgWidgetBuilder might look something like this:
import 'package:json_theme/json_theme_schemas.dart';
class SvgSchema {
static const id =
'https://your-url-here.com/schemas/svg';
static final schema = {
r'$schema': 'http://json-schema.org/draft-06/schema#',
r'$id': '$id',
'title': 'SvgBuilder',
'type': 'object',
'additionalProperties': false,
'properties': {
'asset': SchemaHelper.stringSchema,
'color': SchemaHelper.objectSchema(ColorSchema.id),
'height': SchemaHelper.numberSchema,
'url': SchemaHelper.stringSchema,
'width': SchemaHelper.numberSchema,
},
};
}
Once the builder has been created, it needs to be registered with a JsonWidgetRegistry. This must be done before you ever reference the widget. It's recommended, but not required, that this registration happen in your app's main function.
When registring the widget, you can create a new instance of the registry, or simply get a reference to the default instance, which is the approach below follows.
var registry = JsonWidgetRegistry.instance;
registry.registerCustomBuilder(
SvgBuilder.type,
JsonWidgetBuilderContainer(
builder: SvgBuilder.fromDynamic,
schemaId: SvgSchema.id, // this is optional
),
);
Once the widget is registered, you can safely use the registry to build the widget from JSON. For this example widget, the following JSON would construct an instance:
{
"type": "svg",
"args": {
"asset": "assets/images/visa.svg",
"color": "#fff",
"height": 40,
"width": 56
}
}
Creating Custom Arg Processor #
Custom arg processors are allowing to extend JSON syntax with custom one.
For example let's create the arg processor which will convert "TRUE" and "FALSE" into booleans as a result of JsonWidgetRegistry args processing.
First the ArgProcessor interface has to be implemented.
import 'package:json_dynamic_widget/json_dynamic_widget.dart';
class BooleanStringArgProcessor implements ArgProcessor {
final _matchRegexp = RegExp(r'^TRUE|FALSE$');
@override
bool support(dynamic arg) {
return arg != null && arg is String && _matchRegexp.hasMatch(arg);
}
@override
ProcessedArg process(
JsonWidgetRegistry registry, dynamic arg, Set<String>? listenVariables) {
var resultListenVariables = listenVariables ?? <String>{};
var boolStr = _matchRegexp.firstMatch(arg)!.toString();
return ProcessedArg(
listenVariables: resultListenVariables,
value: boolStr == 'TRUE',
);
}
}
Then such a processor has to be placed into JsonWidgetRegistry.
By default ArgProcessors.defaults are used but there is a possibility to change that via
JsonWidgetRegistry.registerArgProcessors.
var registry = JsonWidgetRegistry.instance;
registry.registerArgProcessors(
<ArgProcessor>[BooleanStringArgProcessor()].addAll(ArgProcessors.defaults)
);
The arg processors are executed from the first to the last one in the list.
To make sure that BooleanStringArgProcessor will be used the best is to add it as a first element of the list.
Metadata
Publisher
Metadata
A library to dynamically generate widgets within Flutter from JSON or other Map-like structures.
Repository (GitHub)
View/report issues
License
unknown (license)
Dependencies
automated_testing_framework, child_builder, collection, expressions, flutter, form_validation, interpolation, json_class, json_conditional, json_schema2, json_theme, logging, meta, uuid
