# Widget Event Capability Overview

The ArkTS widget provides the **postCardAction()** API for interaction between the widget internal and the provider application. Currently, this API supports the router, message, and call events and can be called only in the widget.

![WidgetPostCardAction](figures/WidgetPostCardAction.png)

**Definition**: postCardAction(component: Object, action: Object): void

**Parameters**

| Name| Type| Mandatory| Description|
| -------- | -------- | -------- | -------- |
| component | Object | Yes| Instance of the current custom component. Generally, **this** is transferred.|
| action | Object | Yes| Action description. For details, see the following table.|

**Description of the action parameter**

| Key | Value | Description|
| -------- | -------- | -------- |
| "action" | string | Action type.<br>- **"router"**: redirection to the specified UIAbility of the widget provider.<br>- **"message"**: custom message. If this type of action is triggered, the [onFormEvent()](../reference/apis/js-apis-app-form-formExtensionAbility.md#onformevent) lifecycle callback of the provider FormExtensionAbility is called.<br>- **"call"**: launch of the widget provider in the background. If this type of action is triggered, the specified UIAbility of the widget provider is started in the background, but not displayed in the foreground. This action type requires that the widget provider should have the [ohos.permission.KEEP_BACKGROUND_RUNNING](../security/permission-list.md#ohospermissionkeep_background_running) permission.|
| "bundleName" | string | Name of the target bundle when **action** is **"router"** or **"call"**. This parameter is optional.|
| "moduleName" | string | Name of the target module when **action** is **"router"** or **"call"**. This parameter is optional.|
| "abilityName" | string | Name of the target UIAbility when **action** is **"router"** or **"call"**. This parameter is mandatory.|
| "params" | Object | Additional parameters carried in the current action. The value is a key-value pair in JSON format. For the **"call"** action type, the **method** parameter must be set and its value type must be string. This parameter is mandatory.|


Sample code of the **postCardAction()** API:

```typescript
Button ('Jump')
  .width('40%')
  .height('20%')
  .onClick(() => {
    postCardAction(this, {
      'action': 'router',
      'bundleName': 'com.example.myapplication',
      'abilityName': 'EntryAbility',
      'params': {
        'message': 'testForRouter' // Customize the message to send.
      }
    });
  })

Button ('Start in Background')
  .width('40%')
  .height('20%')
  .onClick(() => {
    postCardAction(this, {
      'action': 'call',
      'bundleName': 'com.example.myapplication',
      'abilityName': 'EntryAbility',
      'params': {
        'method': 'fun', // Set the name of the method to call. It is mandatory.
        'message': 'testForcall' // Customize the message to send.
      }
    });
  })
```


Read on to learn the typical widget development scenarios that can be implemented through widget events.