json_dynamic_widget 1.2.0 
json_dynamic_widget: ^1.2.0 copied to clipboard
peifferinnovations.comA library to dynamically generate widgets within Flutter from JSON or other Map-like structures.
json_dynamic_widget #
Table of Contents #
- Live Example
- Introduction
- Understanding the Registry
- Built In Widgets
- Using Variables
- Dynamic Functions
- Creating Custom Widgets
Live Example #
Introduction #
Widgets that are capable of building themselves from JSON structures. The general structure follows:
{
"type": "<lower_case_type>",
"args": {
"...": "..."
},
"child": {
"...": "..."
},
"children: [{
"...": "...",
}]
}
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.
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.
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 registryo. 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 Variables #
Variables can be defined on the JsonWidgetRegistry that is used to render the dynamic widgets. Within the JSON, the template engine uses the mustache format for variable references. Example: {{variableName}}.
A variable can be used in any of the child / children / args values and for certain types of properties, a variable reference iw 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.
The built in variables are defined below:
| Variable Name | Example | Description |
|---|---|---|
*curve_name*_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 #
Similar to the variables, the JsonWidgetRegistry supports registering dynamic functions that can be called to create values. If a value is a dynamic function then it must begin and end with two pound signs: ##. For example: ##set_value(variableName, 5)##. Dynamic values can refer to variables using the mustache format.
The built in functions are defined below:
| Function Name | Example | Args | Description |
|---|---|---|---|
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. |
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
}
}
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
child_builder, flutter, form_validation, json_class, json_conditional, json_schema, json_theme, logging, meta
