> The startup mode of the callee must be **singleton**.
> Currently, only system applications and Service Extension abilities can use the **Call** APIs to access the callee.
## Available APIs
The table below describes the ability call APIs. For details, see [Ability](../reference/apis/js-apis-application-ability.md#caller).
**Table 1** Ability call APIs
|API|Description|
|:------|:------|
|Promise<Caller> startAbilityByCall(want: Want)|Obtains the caller interface of the specified ability, and if the specified ability is not started, starts the ability in the background.|
|Promise<Caller> startAbilityByCall(want: Want)|Obtains the caller interface of the specified ability and, if the specified ability is not running, starts the ability in the background.|
|void on(method: string, callback: CalleeCallBack)|Callee.on: callback invoked when the callee registers a method.|
|void off(method: string)|Callee.off: callback invoked when the callee deregisters a method.|
|Promise<void> call(method: string, data: rpc.Sequenceable)|Caller.call: sends agreed sequenceable data to the callee.|
...
...
@@ -77,7 +81,7 @@ export default class MySequenceable {
```
4. Implement **Callee.on** and **Callee.off**.
The time to register a listener for the callee depends on your application. The data sent and received before the listener is registered and that after the listener is deregistered are not processed. In the following example, the **CalleeSortMethod** listener is registered in **onCreate** of the ability and deregistered in **onDestroy**. After receiving sequenceable data, the application processes the data and returns them. You need to implement processing based on service requirements. The sample code is as follows:
The time to register a listener for the callee depends on your application. The data sent and received before the listener is registered and that after the listener is deregistered are not processed. In the following example, the **CalleeSortMethod** listener is registered in **onCreate** of the ability and deregistered in **onDestroy**. After receiving sequenceable data, the application processes the data and returns the data result. You need to implement processing based on service requirements. The sample code is as follows:
The sequenceable data can be sent to the callee in either of the following ways: without a return value or obtaining data returned by the callee. The method and sequenceable data must be consistent with those of the callee. The following example describes how to invoke the **Call** API to send data to the callee. The sample code is as follows:
The sequenceable data can be sent to the callee with or without a return value. The method and sequenceable data must be consistent with those of the callee. The following example describes how to invoke the **Call** API to send data to the callee. The sample code is as follows:
```ts
constMSG_SEND_METHOD:string='CallSendMsg'
asynconButtonCall(){
...
...
@@ -242,9 +246,6 @@ try {
}
```
## Development Example
## Samples
The following sample is provided to help you better understand how to develop an ability call in the stage model:
In this sample, the **AbilityStage** APIs are implemented in the **AbilityStage.ts** file in the **Application** directory, the **Ability** APIs are implemented in the **MainAbility** directory, and **pages/index** is the pages of the ability. Another ability and callee are implemented in the **CalleeAbility** directory, and its pages are the content configured in **pages/second**. The **MainAbility** functions as the caller, and the **CalleeAbility** functions as the callee. After starting the **CalleeAbility**, the **MainAbility** obtains the caller interface, processes the string entered by the user, and transfers the processed string to the **CalleeAbility**. The **CalleeAbility** refreshes the page based on the received data and returns the result to the **MainAbility**.
-[`StageCallAbility`: Stage Ability Creation and Usage (eTS, API version 9)](https://gitee.com/openharmony/app_samples/tree/master/ability/StageCallAbility)
