# PageAbility开发指导

## 概述
### 功能简介
PageAbility是具备ArkUI实现的Ability，是开发者具体可见并可以交互的Ability实例，开发者通过IDE创建Ability时，IDE会自动创建相关模板代码。PageAbility相关能力通过单例featureAbility暴露，生命周期相关回调通过app.js/app.ets中回调函数暴露。

### PageAbility的生命周期

**Ability生命周期介绍**（Ability Life Cycle）：

Ability生命周期是Ability被调度到INACTIVE、ACTIVE、BACKGROUND等各个状态的统称。PageAbility生命周期流转如下图所示：

![PageAbility-Lifecycle](figures/page-ability-lifecycle.png)


**Ability生命周期状态说明：**

  - **UNINITIALIZED**：未初始状态，为临时状态，Ability被创建后会由UNINITIALIZED状态进入INITIAL状态。

  - **INITIAL**：初始化状态，也表示停止状态，表示当前Ability未运行，Ability被启动后由INITIAL态进入INACTIVE状态。

  - **INACTIVE**：失去焦点状态，表示当前窗口已显示但是无焦点状态。

  - **ACTIVE**：前台激活状态，表示当前窗口已显示，并获取焦点。

  - **BACKGROUND**：后台状态，表示当前Ability退到后台，Ability在被销毁后由BACKGROUND状态进入INITIAL状态，或者重新被激活后由BACKGROUND状态进入ACTIVE状态。

**PageAbility生命周期回调与生命周期状态的关系如下图所示：**

![fa-pageAbility-lifecycle](figures/fa-pageAbility-lifecycle.png)

PageAbility提供命周期回调，开发者可以在`app.js/app.ets`中重写生命周期相关回调函数 。

## 开发指导
### featureAbility接口说明

**表1** featureAbility接口介绍

| 接口名                                              | 描述            |
| --------------------------------------------------- | --------------- |
| void startAbility(parameter: StartAbilityParameter) | 启动Ability     |
| Context getContext():                               | 获取应用Context |
| void terminateSelf()                                | 结束Ability     |
| bool hasWindowFocus()                               | 是否获取焦点    |


### 启动本地PageAbility

**导入模块**

```js
  import featureAbility from '@ohos.ability.featureAbility'
```

**示例**

```javascript
  import featureAbility from '@ohos.ability.featureAbility'
  featureAbility.startAbility({
  want:
  {
    action: "",
    entities: [""],
    type: "",
    options: {
      // Grant the permission to perform read operations on the URI.
      authReadUriPermission: true,
      // Grant the permission to perform write operations on the URI.
      authWriteUriPermission: true,
      // support forwarding the intent result to the ability.
      abilityForwardResult: true,
      // Enable abiligy continuation.
      abilityContinuation: true,
      // Specify that a component does not belong to ohos.
      notOhosComponent: true,
      // Specify that an ability is started.
      abilityFormEnabled: true,
      // Grant the permission for possible persisting on the URI.
      authPersistableUriPermission: true,
      // Grant the permission for possible persisting on the prefix URI.
      authPrefixUriPermission: true,
      // Support distributed scheduling system startup on multiple devices.
      abilitySliceMultiDevice: true,
      // A service ability is started regardless of whether the host application has been started.
      startForegroundAbility: true,
      // Install the specified ability if it is not installed.
      installOnDemand: true,
      // Return the result to the ability slice.
      abilitySliceForwardResult: true,
      // Install the specified ability with background mode if it is not installed.
      installWithBackgroundMode: true
    },
    deviceId: "",
    bundleName: "com.example.startability",
    abilityName: "com.example.startability.MainAbility",
    uri: ""
  },
  },
  );
```

`want`参数也可以使用parameters参数，使用key-value的方式输入。
**示例**

```javascript
  import featureAbility from '@ohos.ability.featureAbility'
  featureAbility.startAbility({
    want:
    {
        bundleName: "com.example.startability",
        uri: "",
        parameters: {
            abilityName: "com.example.startability.MainAbility"
        }
    },
  },
  );
```
### 启动远程PageAbility（当前仅对系统应用开放）
>说明：由于DeviceManager的getTrustedDeviceListSync接口仅对系统应用开放，当前启动远程PageAbility仅支持系统应用

**导入模块**

```
  import featureAbility from '@ohos.ability.featureAbility'
  import deviceManager from '@ohos.distributedHardware.deviceManager';
```

**示例**
```ts
  function onStartRemoteAbility() {
  console.info('onStartRemoteAbility begin');
  var params;
  var wantValue = {
    bundleName: 'ohos.samples.etsDemo',
    abilityName: 'ohos.samples.etsDemo.RemoteAbility',
    deviceId: getRemoteDeviceId(),
    parameters: params
  };
  console.info('onStartRemoteAbility want=' + JSON.stringify(wantValue));
  featureAbility.startAbility({
    want: wantValue
  }).then((data) => {
    console.info('onStartRemoteAbility finished, ' + JSON.stringify(data));
  });
  console.info('onStartRemoteAbility end');
  }
```

从DeviceManager获取`deviceId`，具体示例代码如下：
```ts
  import deviceManager from '@ohos.distributedHardware.deviceManager';
  var dmClass;
  function getRemoteDeviceId() {
    if (typeof dmClass === 'object' && dmClass != null) {
        var list = dmClass.getTrustedDeviceListSync();
        if (typeof (list) == 'undefined' || typeof (list.length) == 'undefined') {
            console.log("MainAbility onButtonClick getRemoteDeviceId err: list is null");
            return;
        }
        console.log("MainAbility onButtonClick getRemoteDeviceId success:" + list[0].deviceId);
        return list[0].deviceId;
    } else {
        console.log("MainAbility onButtonClick getRemoteDeviceId err: dmClass is null");
    }
  }
```

在跨设备场景下，需要向开发者申请数据同步的权限。具体示例代码如下：
```ts
  import accessControl from "@ohos.abilityAccessCtrl";
  import bundle from '@ohos.bundle';
  async function RequestPermission() {
  console.info('RequestPermission begin');
  let array: Array<string> = ["ohos.permission.DISTRIBUTED_DATASYNC"];
  var bundleFlag = 0;
  var tokenID = undefined;
  var userID = 100;
  var appInfo = await bundle.getApplicationInfo('ohos.samples.etsDemo', bundleFlag, userID);
  tokenID = appInfo.accessTokenId;
  var atManager = abilityAccessCtrl.createAtManager();
  let requestPermissions: Array<string> = [];
  for (let i = 0;i < array.length; i++) {
    var result = await atManager.verifyAccessToken(tokenID, array[i]);
    console.info("verifyAccessToken result:" + JSON.stringify(result));
    if (result == abilityAccessCtrl.GrantStatus.PERMISSION_GRANTED) {
    } else {
      requestPermissions.push(array[i]);
    }
  }
  console.info("requestPermissions:" + JSON.stringify(requestPermissions));
  if (requestPermissions.length == 0 || requestPermissions == []) {
    return;
  }
  let context = featureAbility.getContext();
  context.requestPermissionsFromUser(requestPermissions, 1, (data)=>{
    console.info("data:" + JSON.stringify(data));
    console.info("data requestCode:" + data.requestCode);
    console.info("data permissions:" + data.permissions);
    console.info("data authResults:" + data.authResults);
  });
  console.info('RequestPermission end');
  }
```

### 生命周期接口说明
**表2** 生命周期回调函数介绍

| 接口名       | 描述                                                         |
| ------------ | ------------------------------------------------------------ |
| onShow()     | Ability由后台不可见状态切换到前台可见状态调用onShow方法，此时开发者在屏幕可以看到该Ability |
| onHide()     | Ability由前台切换到后台不可见状态时调用onHide方法，此时开发者在屏幕看不到该Ability。 |
| onDestroy()  | 应用退出，销毁Ability对象前调用onDestroy方法，开发者可以在该方法里做一些回收资源、清空缓存等应用退出前的准备工作。 |
| onCreate()   | Ability第一次启动创建Ability时调用onCreate方法，开发者可以在该方法里做一些应用初始化工作。 |
| onInactive() | Ability失去焦点时调用onInactive方法，Ability在进入后台状态时会先失去焦点，再进入后台。 |
| onActive()   | Ability切换到前台，并且已经获取焦点时调用onActive方法。      |

**示例**
开发者需要重写`app.js/app.ets`中相关生命周期回调函数，IDE模板默认生成`onCreate()`和`onDestroy()`方法，其他方法需要开发者自行实现。

```javascript
export default {
  onCreate() {
    console.info('Application onCreate')
  },
  onDestroy() {
    console.info('Application onDestroy')
  },
  onShow(){
    console.info('Application onShow')
  },
  onHide(){
    console.info('Application onHide')
  },
  onInactive(){
    console.info('Application onInactive')
  },
  onActive(){
    console.info('Application onActive')
  },
}
```
### 开发实例
针对pageAbility开发，有以下示例工程可供参考：

[DMS](https://gitee.com/openharmony/app_samples/tree/master/ability/DMS)

在本示例中完整展示了启动本地Ability、启动远程Ability的使用方法。