RemoteView – Android系統內部通訊機制

一、Remote

Remote（遠程的）是Android系統提供的一種跨進程通信（IPC）機制，允許一個應用程序（或進程）調用另一個進程中的服務或UI元素。通過Remote機制，應用程序可以像訪問本地服務或UI元素一樣訪問遠程服務或UI元素，這為Android應用程序開發提供了更多的靈活性。

二、Remotely

Android提供了兩種方式實現對Remote的遠程訪問，一種是通過AIDL（Android介面定義語言）生成Java介面的方式，另一種則是通過RemoteView實現。

三、Remote Control

RemoteView（遠程視圖）是一種特殊的View，使用它可以在一個進程中創建一個View，然後將該View在另一個進程中顯示。RemoteView在設計上基本和普通View一致，能夠支持大部分的View功能和屬性，但是有一定的限制，例如：

- 不支持自定義的繪製代碼
- 只支持一部分的View屬性，如：layout_width、layout_height、background、padding等屬性
- 只能訪問遠程進程中已經註冊的布局文件或View ID
- 只能更新布局中已存在的View（即不能動態增加Views） 

四、Remote軟體下載

在實際應用中，如果需要在一個應用程序中訪問另一個應用程序中的RemoteView，我們需要在另一個應用程序中註冊一個RemoteView布局文件或者View ID，並在需要顯示該View的時候，通過RemoteViews類構造遠程視圖，然後通過AppWidgetManager來更新該遠程視圖。下面是一個註冊RemoteView布局文件並展示的示例代碼：

// 在另一個進程中的RemoteService中註冊RemoteView布局
public class RemoteService extends Service {
 
    private static final int LAYOUT_ID = R.layout.remote_view_layout;

    @Override
    public IBinder onBind(Intent intent) {
        return new RemoteBinder();
    }

    private class RemoteBinder extends IRemoteBinder.Stub() {
 
        @Override
        public RemoteViews getRemoteView() throws RemoteException {
            RemoteViews remoteViews = new RemoteViews(getApplicationContext().getPackageName(), LAYOUT_ID);
            // 設置點擊事件
            Intent intent = new Intent(getApplicationContext(), RemoteActivity.class);
            PendingIntent pendingIntent = PendingIntent.getActivity(getApplicationContext(), 0, intent, 0);
            remoteViews.setOnClickPendingIntent(R.id.button, pendingIntent);
            return remoteViews;
        }
    }
}

// 在本地應用程序中通過RemoteViews獲取遠程視圖並展示
public class LocalActivity extends Activity {
 
    private static final String PACKAGE_NAME = "com.example.remote";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
 
        AppWidgetManager manager = AppWidgetManager.getInstance(this);
        RemoteViews remoteViews = new RemoteViews(PACKAGE_NAME, R.layout.remote_view_layout);
        ComponentName componentName = new ComponentName(PACKAGE_NAME, RemoteService.class.getName());
        // 獲取另一個進程中RemoteService返回的RemoteViews
        remoteViews = manager.getAppWidgetOptions(componentName).getBoolean(AppWidgetManager.OPTION_APPWIDGET_HOST_CATEGORY, false)
                ? manager.createWidget(this, R.xml.widget_gadget) : remoteViews;
        // 更新本地View
        ViewGroup viewGroup = findViewById(R.id.container);
        viewGroup.addView(remoteViews.apply(this, viewGroup));
    }
}

五、Remove

除了RemoteView，在使用AIDL調用Remote服務時，我們也可以在Binder中返回RemoteView，這樣就能在服務端創建一個View，然後在客戶端中展示。

// 服務端實現
public class RemoteService extends Service {

    @Override
    public IBinder onBind(Intent intent) {
        return new RemoteBinder();
    }

    private class RemoteBinder extends IRemoteBinder.Stub() {

        @Override
        public RemoteViews getRemoteView() throws RemoteException {
            // 創建一個RemoteView並返回
            RemoteViews remoteViews = new RemoteViews(getApplicationContext().getPackageName(), R.layout.remote_view_layout);
            return remoteViews;
        }

        @Override
        public IBinder getRemoteBinder() throws RemoteException {
            // 返回帶有遠程View的Binder
            return new RemoteViewBinder(new RemoteViews(getApplicationContext().getPackageName(), R.layout.remote_view_layout));
        }
    }

    // 返回帶有遠程View的Binder
    private class RemoteViewBinder extends IRemoteBinder.Stub() {
        RemoteViews remoteViews;

        public RemoteViewBinder(RemoteViews remoteViews) {
            this.remoteViews = remoteViews;
        }

        @Override
        public RemoteViews getRemoteView() throws RemoteException {
            return remoteViews;
        }
    }
}

// 客戶端實現
public class LocalActivity extends Activity {

    IRemoteBinder remoteService;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // 綁定RemoteService服務
        Intent intent = new Intent(this, RemoteService.class);
        bindService(intent, conn, Context.BIND_AUTO_CREATE);
    }

    private ServiceConnection conn = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            remoteService = IRemoteBinder.Stub.asInterface(service);
            try {
                // 獲取帶有遠程View的Binder
                IRemoteBinder remoteBinder = remoteService.getRemoteBinder();
                // 展示遠程View
                RemoteViews remoteViews = remoteBinder.getRemoteView();
                ViewGroup viewGroup = findViewById(R.id.container);
                viewGroup.addView(remoteViews.apply(getApplicationContext(), viewGroup));
            } catch (RemoteException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {

        }
    };
}