A Form ability presents a widget, which is a set of UI components used to display important information or operations for an application. It provides users with direct access to a desired application service, without requiring them to open the application.
A widget displays brief information about an application on the UI of another application (host application, currently system applications only) and provides basic interactive features such as opening a UI page or sending a message. The widget client is responsible for displaying the service widget.
Basic concepts:
- Widget provider
The widget provider is an atomic service that provides the content to be displayed. It controls the display content, component layout, and component click events of a widget.
- Widget client
The widget client is an application that displays the widget content and controls the position where the widget is displayed in the host application.
- Widget Manager
The Widget Manager is a resident agent that manages widgets added to the system and provides functions such as periodic widget update.
> The widget client and provider do not keep running all the time. The Widget Manager starts the widget provider to obtain widget information when a widget is added, deleted, or updated.
You only need to develop widget content as the widget provider. The system automatically handles the work done by the widget client and Widget Manager.
The widget provider controls the widget content to display, component layout, and click events bound to components.
## Scenario
Form ability development refers to the development conducted by the widget provider based on the Feature Ability (FA) model(fa-brief.md). As a widget provider, you need to carry out the following operations:
- Develop the lifecycle callback functions in **FormAbility**.
- Create a **FormBindingData** object.
- Update a widget through **FormProvider**.
- Develop the widget UI page.
## Available APIs
The table below describes the lifecycle callback functions provided **FormAbility**.
| setFormNextRefreshTime(formId: string, minute: number, callback: AsyncCallback<void>): void; | Sets the next refresh time for a widget. This API uses an asynchronous callback to return the result. |
| setFormNextRefreshTime(formId: string, minute: number): Promise<void>; | Sets the next refresh time for a widget. This API uses a promise to return the result.|
| updateForm(formId: string, formBindingData: FormBindingData, callback: AsyncCallback<void>): void; | Updates a widget. This API uses an asynchronous callback to return the result. |
| updateForm(formId: string, formBindingData: FormBindingData): Promise<void>; | Updates a widget. This API uses a promise to return the result. |
## How to Develop
### Creating a Form Ability
To create a widget in the FA model, you need to implement the lifecycle callback functions of **FormAbility**. The sample code is as follows:
// Called when the widget client converts the temporary widget into a normal one. The widget provider should do something to respond to the conversion.
console.log('FormAbility onCastToNormal');
},
onUpdate(formId){
// To support scheduled update, periodic update, or update requested by the widget client for a widget, override this method for data update.
// Called when the widget client initiates an event about visibility changes. The widget provider should do something to respond to the notification.
console.log('FormAbility onVisibilityChange');
},
onEvent(formId,message){
// If the widget supports event triggering, override this method and implement the trigger.
console.log('FormAbility onEvent');
},
onDestroy(formId){
// Delete widget data.
console.log('FormAbility onDestroy');
},
onAcquireFormState(want){
console.log('FormAbility onAcquireFormState');
returnformInfo.FormState.READY;
},
}
```
### Configuring config.json for the Form Ability
Configure the **config.json** file for the **Form** ability.
- The **js** module in the **config.json** file provides the JavaScript resources of the **Form** ability. The internal field structure is described as follows:
| name | Name of a JavaScript component. The default value is **default**. | String | No |
| pages | Route information about all pages in the JavaScript component, including the page path and page name. The value is an array, in which each element represents a page. The first element in the array represents the home page of the JavaScript FA.| Array | No |
| window | Window-related configurations. This field applies only to phones, tablets, smart TVs, head units, and wearable devices.| Object | Yes |
| type | Type of the JavaScript component. Available values are as follows:<br>**normal**: indicates that the JavaScript component is an application instance.<br>**form**: indicates that the JavaScript component is a widget instance.| String | Yes (initial value: **normal**)|
| mode | Development mode of the JavaScript component. | Object | Yes (initial value: left empty) |
A configuration example is as follows:
```json
"js":[{
"name":"widget",
"pages":["pages/index/index"],
"window":{
"designWidth":720,
"autoDesignWidth":true
},
"type":"form"
}]
```
- The **abilities** module in the **config.json** file corresponds to the **Form** ability. The internal field structure is described as follows:
| name | Class name of the widget. The value is a string with a maximum of 127 bytes. | String | No |
| description | Description of the widget. The value can be a string or a resource index to descriptions in multiple languages. The value is a string with a maximum of 255 bytes.| String | Yes (initial value: left empty) |
| isDefault | Whether the widget is a default one. Each ability has only one default widget.<br>**true**: The widget is the default one.<br>**false**: The widget is not the default one.| Boolean | No |
| type | Type of the widget. Available values are as follows:<br>**Java**: indicates a Java-programmed widget.<br>**JS**: indicates a JavaScript-programmed widget.| String | No |
| colorMode | Color mode of the widget. Available values are as follows:<br>**auto**: The widget adopts the auto-adaptive color mode.<br>**dark**: The widget adopts the dark color mode.<br>**light**: The widget adopts the light color mode.| String | Yes (initial value: **auto**)|
| supportDimensions | Grid styles supported by the widget. Available values are as follows:<br>1 * 2: indicates a grid with one row and two columns.<br>2 * 2: indicates a grid with two rows and two columns.<br>2 * 4: indicates a grid with two rows and four columns.<br>4 * 4: indicates a grid with four rows and four columns.| String array| No |
| defaultDimension | Default grid style of the widget. The value must be available in the **supportDimensions** array of the widget.| String | No |
| landscapeLayouts | Landscape layouts for the grid styles. Values in this array must correspond to the values in the **supportDimensions** array. This field is required only by Java-programmed widgets.| String array| No |
| portraitLayouts | Portrait layouts for the grid styles. Values in this array must correspond to the values in the **supportDimensions** array. This field is required only by Java-programmed widgets.| String array| No |
| updateEnabled | Whether the widget can be updated periodically. Available values are as follows:<br>**true**: The widget can be updated periodically, depending on the update way you select, either at a specified interval (**updateDuration**) or at the scheduled time (**scheduledUpdateTime**). **updateDuration** is preferentially recommended.<br>**false**: The widget cannot be updated periodically.| Boolean | No |
| scheduledUpdateTime | Scheduled time to update the widget. The value is in 24-hour format and accurate to minute. | String | Yes (initial value: **0:0**) |
| updateDuration | Interval to update the widget. The value is a natural number, in the unit of 30 minutes.<br>If the value is **0**, this field does not take effect.<br>If the value is a positive integer ***N***, the interval is calculated by multiplying ***N*** and 30 minutes.| Number | Yes (initial value: **0**) |
| formConfigAbility | Name of the facility or activity used to adjust a widget. | String | Yes (initial value: left empty) |
| formVisibleNotify | Whether the widget is allowed to use the widget visibility notification. | String | Yes (initial value: left empty) |
| jsComponentName | Component name of the widget. The value is a string with a maximum of 127 bytes. This field is required only by JavaScript-programmed widgets.| String | No |
| metaData | Metadata of the widget. This field contains the array of the **customizeData** field. | Object | Yes (initial value: left empty) |
| customizeData | Custom information about the widget. | Object array | Yes (initial value: left empty) |
A configuration example is as follows:
```json
"abilities":[{
"name":"FormAbility",
"description":"This is a FormAbility",
"formsEnabled":true,
"icon":"$media:icon",
"label":"$string:form_FormAbility_label",
"srcPath":"FormAbility",
"type":"service",
"forms":[{
"colorMode":"auto",
"defaultDimension":"2*2",
"description":"This is a service widget.",
"formVisibleNotify":true,
"isDefault":true,
"jsComponentName":"widget",
"name":"widget",
"scheduledUpdateTime":"10:30",
"supportDimensions":["2*2"],
"type":"JS",
"updateDuration":1,
"updateEnabled":true
}]
}]
```
### Widget Data Persistence
Mostly, the widget provider is started only when it needs to obtain information about a widget. The Widget Manager supports multi-instance management and uses the widget ID to identify an instance. If the widget provider supports widget data modification, it must persistently store the data based on the widget ID, so that it can access the data of the target widget when obtaining, updating, or starting a widget.
You should override **onDestroy** to delete widget data.
```javascript
onDestroy(formId){
// Delete widget data.
deleteFormInfo(formId);
console.log('FormAbility onDestroy');
}
```
For details about the persistence method, see [Lightweight Data Store Development](../database/database-preference-guidelines.md).
Note that the **Want** passed by the widget client to the widget provider contains a temporary flag, indicating whether the requested widget is a temporary one.
Normal widget: a widget that will be persistently used by the widget client
Temporary widget: a widget that is temporarily used by the widget client
Data of a temporary widget is not persistently stored. If the widget framework is killed and restarted, data of a temporary widget will be deleted. However, the widget provider is not notified of which widget is deleted, and still keeps the data. Therefore, the widget provider should implement data clearing. In addition, the widget client may convert a temporary widget into a normal one. If the conversion is successful, the widget provider should process the widget ID and store the data persistently. This prevents the widget provider from deleting persistent data when clearing temporary widgets.
### Developing the Widget UI Page
You can use HML, CSS, and JSON to develop the UI page for a JavaScript-programmed widget.
