# FormExtension

> **NOTE**
> 
> The initial APIs of this module are supported since API version 9. Newly added APIs will be marked with a superscript to indicate their earliest API version. 
> The APIs of this module can be used only in the stage model.

Provides **FormExtension** APIs.

## Modules to Import

```
import FormExtension from '@ohos.application.FormExtension';
```

## Required Permissions

None

## Attributes

**System capability**: SystemCapability.Ability.Form

| Name   | Type                                               | Readable| Writable| Description                                               |
| ------- | ------------------------------------------------------- | ---- | ---- | --------------------------------------------------- |
| context | [FormExtensionContext](js-apis-formextensioncontext.md) | Yes  | No  | Context of the **FormExtension**. This context is inherited from **ExtensionContext**.|

## onCreate

onCreate(want: Want): formBindingData.FormBindingData

Called to notify the widget provider that a **Form** instance (widget) has been created.

**System capability**: SystemCapability.Ability.Form

**Parameters**

  | Name| Type                                  | Mandatory| Description                                                        |
  | ------ | -------------------------------------- | ---- | ------------------------------------------------------------ |
  | want   | [Want](js-apis-application-Want.md) | Yes  | Information related to the extension, including the widget ID, name, and style. The information must be managed as persistent data to facilitate subsequent widget update and deletion.|

**Return value**

  | Type                                                        | Description                                                       |
  | ------------------------------------------------------------ | ----------------------------------------------------------- |
  | [formBindingData.FormBindingData](js-apis-formbindingdata.md#formbindingdata) | A **formBindingData.FormBindingData** object containing the data to be displayed on the widget.|

**Example**

  ```js
  import formBindingData from '@ohos.application.formBindingData'
  export default class MyFormExtension extends FormExtension {
      onCreate(want) {
          console.log('FormExtension onCreate, want:' + want.abilityName);
          let dataObj1 = {
              temperature:"11c",
              "time":"11:00"
          };
          let obj1 = formBindingData.createFormBindingData(dataObj1);
          return obj1;
      }
  }
  ```

## FormExtension.onCastToNormal

onCastToNormal(formId: string): void

Called to notify the widget provider that a temporary widget has been converted to a normal one.

**System capability**: SystemCapability.Ability.Form

**Parameters**

  | Name| Type  | Mandatory| Description                    |
  | ------ | ------ | ---- | ------------------------ |
  | formId | string | Yes  | ID of the widget that requests to be converted to a normal one.|

**Example**

  ```
  export default class MyFormExtension extends FormExtension {
      onCastToNormal(formId) {
          console.log('FormExtension onCastToNormal, formId:' + formId);
      }
  }
  ```

## FormExtension.onUpdate

onUpdate(formId: string): void

Called to notify the widget provider that a widget has been updated. After obtaining the latest data, the caller invokes **updateForm** of the [FormExtensionContext](js-apis-formextensioncontext.md) class to update the widget data.

**System capability**: SystemCapability.Ability.Form

**Parameters**

  | Name| Type  | Mandatory| Description              |
  | ------ | ------ | ---- | ------------------ |
  | formId | string | Yes  | ID of the widget that requests to be updated.|

**Example**

  ```js
  import formBindingData from '@ohos.application.formBindingData'
  export default class MyFormExtension extends FormExtension {
      onUpdate(formId) {
          console.log('FormExtension onUpdate, formId:' + formId);
          let obj2 = formBindingData.createFormBindingData({temperature:"22c", time:"22:00"});
          this.context.updateForm(formId, obj2)
              .then((data)=>{
                  console.log('FormExtension context updateForm, data:' + data);
              }).catch((error) => {
              console.error('Operation updateForm failed. Cause: ' + error);});
      }
  }
  ```

## FormExtension.onVisibilityChange

onVisibilityChange(newStatus: { [key: string]: number }): void

Called to notify the widget provider of the change of visibility.

**System capability**: SystemCapability.Ability.Form

**Parameters**

  | Name   | Type                     | Mandatory| Description                        |
  | --------- | ------------------------- | ---- | ---------------------------- |
  | newStatus | { [key: string]: number } | Yes  | ID and visibility status of the widget to be changed.|

**Example**

  ```js
    import formBindingData from '@ohos.application.formBindingData'
  export default class MyFormExtension extends FormExtension {
      onVisibilityChange(newStatus) {
          console.log('FormExtension onVisibilityChange, newStatus:' + newStatus);
          let obj2 = formBindingData.createFormBindingData({temperature:"22c", time:"22:00"});
  
          for (let key in newStatus) {
              console.log('FormExtension onVisibilityChange, key:' + key + ", value=" + newStatus[key]);
              this.context.updateForm(key, obj2)
                  .then((data)=>{
                      console.log('FormExtension context updateForm, data:' + data);
                  }).catch((error) => {
                  console.error('Operation updateForm failed. Cause: ' + error);});
          }
      }
  }
  ```

## FormExtension.onEvent

onEvent(formId: string, message: string): void

Called to instruct the widget provider to receive and process the widget event.

**System capability**: SystemCapability.Ability.Form

**Parameters**

  | Name | Type  | Mandatory| Description                  |
  | ------- | ------ | ---- | ---------------------- |
  | formId  | string | Yes  | ID of the widget that requests the event.|
  | message | string | Yes  | Event message.            |

**Example**

  ```js
  export default class MyFormExtension extends FormExtension {
      onEvent(formId, message) {
          console.log('FormExtension onEvent, formId:' + formId + ", message:" + message);
      }
  }
  ```

## FormExtension.onDestroy

onDestroy(formId: string): void

Called to notify the widget provider that a **Form** instance (widget) has been destroyed.

**System capability**: SystemCapability.Ability.Form

**Parameters**

  | Name| Type  | Mandatory| Description              |
  | ------ | ------ | ---- | ------------------ |
  | formId | string | Yes  | ID of the widget to be destroyed.|

**Example**

  ```js
  export default class MyFormExtension extends FormExtension {
      onDestroy(formId) {
          console.log('FormExtension onDestroy, formId:' + formId);
      }
  }
  ```

## FormExtension.onConfigurationUpdated

onConfigurationUpdated(config: Configuration): void;

Called when the configuration of the environment where the ability is running is updated.

**System capability**: SystemCapability.Ability.Form

**Parameters**

  | Name| Type| Mandatory| Description| 
  | -------- | -------- | -------- | -------- |
  | config | [Configuration](#section188911144124715) | Yes| New configuration.| 

**Example**
    
  ```js
  class MyFormExtension extends FormExtension {
      onConfigurationUpdated(config) {
          console.log('onConfigurationUpdated, config:' + JSON.stringify(config));
      }
  }
  ```

  ## FormExtension.onAcquireFormState

onAcquireFormState?(want: Want): formInfo.FormState;

Called when the widget provider receives the status query result of a specified service widget. By default, the initial state is returned.

**System capability**: SystemCapability.Ability.Form

**Parameters**

  | Name| Type| Mandatory| Description| 
  | -------- | -------- | -------- | -------- |
  | want | [Want](js-apis-application-Want.md) | No| Description of the widget state, including the bundle name, ability name, module name, widget name, and widget dimension.| 

**Example**
    
  ```js
  import fromInfo from '@ohos.application.fromInfo'
  class MyFormExtension extends FormExtension {
      onAcquireFormState(want) {
          console.log('FormExtension onAcquireFormState, want:' + want);
          return fromInfo.FormState.UNKNOWN;
      }
  }
  ```