SystemUI-应用知栏视图是如何夸进程显示? ?>

SystemUI-应用知栏视图是如何夸进程显示?

应用知栏视图是如何夸进程显示到 SystemUI 的?

跨进程通讯的基础是 IPC ,通知服务(NotificationManagerService, 简称 NMS)也不离开 IPC ,核心架构还是 IPC 架构。

消息通道

  1. 应用做作为通知的发送端, 需要调用 NMS ,发通知。例如:
      String channelId = "channel_1";
      String tag = "ailabs";
      int id = 10086;
      int importance = NotificationManager.IMPORTANCE_LOW;
      NotificationChannel channel = new NotificationChannel(channelId, "123", importance);
      NotificationManager manager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
      manager.createNotificationChannel(channel);
      Notification notification = new Notification.Builder(MainActivity.this, channelId)
              .setCategory(Notification.CATEGORY_MESSAGE)
              .setSmallIcon(R.mipmap.ic_launcher)
              .setContentTitle("This is a content title")
              .setContentText("This is a content text")
              .setAutoCancel(true)
              .build();
       // 通知栏要显示的视图布局
      RemoteViews remoteViews = new RemoteViews(getPackageName(), R.layout.layout_remoteviews);                 
      notification.contentView = remoteViews;
      manager.notify(tag, id , notification);
    
  2. SystemUI 作为通知的接收放需要注册监听器 INotificationListener 是监听通通知的一个 AIDL 接口,
    NotificationListenerService 是一个监听管理服务,他的内部类 NotificationListenerWrapper 实现了
    INotificationListener 接口。 例如:

    /** @hide */
    protected class NotificationListenerWrapper extends INotificationListener.Stub {
    @Override
    public void onNotificationPosted(IStatusBarNotificationHolder sbnHolder,
    NotificationRankingUpdate update) {
    // 接收通知
    ….
    省略了很多代码
    }

        @Override
        public void onNotificationRemoved(IStatusBarNotificationHolder sbnHolder,
                NotificationRankingUpdate update, NotificationStats stats, int reason) {
                // 删除通知
                      ....
                 // 省略了很多代码
        }
    

这个通知监听需要向 NMS 注册:

   @SystemApi
      public void registerAsSystemService(Context context, ComponentName componentName,
              int currentUser) throws RemoteException {
          if (mWrapper == null) {
              mWrapper = new NotificationListenerWrapper();
          }
          mSystemContext = context;
          INotificationManager noMan = getNotificationInterface();
          mHandler = new MyHandler(context.getMainLooper());
          mCurrentUser = currentUser;
          noMan.registerListener(mWrapper, componentName, currentUser);
      }

以上是 Android 为我们提供的通知接收管理服务类, SystemUI 有个NotificationListenerWithPlugins 类继承了 NotificationListenerService
类。 并在 SystemUI 进程起来的时候调用 registerAsSystemService() 方法完成了注册:

NotificationListenerWithPlugins mNotificationListener = new NotificationListenerWithPlugins();
mNotificationListener.registerAsSystemService();

这样通道就建立起来了。

消息传递过程,大家可以按照这个思路器走读源码

RemoteViews

以上只是讲解了应用怎么把一个消息传递到 SystemUI , 理解 IPC 通讯的不难理解。 而神奇之处在于显示的视图布局明明是定义在一个应用中,为何能跨进程显示到 SystemUI 进程中呢?

发送通知, 传递的通知实体是 Notification 的实例, Notification 实现了 Parcelable 接口。 Notification 有个 RemoteViews 的成员变量

RemoteViews remoteViews = new RemoteViews(getPackageName(), R.layout.layout_remoteviews);
notification.contentView = remoteViews;

RemoteViews 也实现了 Parcelable 接口, 主要是封装了通知栏要展示的视图信息, 例如, 应用包名、布局ID。我们都知道实现了 Parcelable 这个接口就可以在 IPC 通道上夸进程传递。 RemoteView 支持的布局类型也是有限的,例如在 8.0 上仅支持如下类型:

  • android.widget.AdapterViewFlipper
  • android.widget.FrameLayout
  • android.widget.GridLayout
  • android.widget.GridView
  • android.widget.LinearLayout
  • android.widget.ListView
  • android.widget.RelativeLayout
  • android.widget.StackView
  • android.widget.ViewFlipper

    RemoteView 携带了视图信息, 进程间传递的并不是真实的视图对象, 而主要是布局的 id ,那么显示在通知栏上的视图对象又是如何创建出来的呢?

    通知视图创建

    在通知的接收端创建的,上文说过 NotificationManagerService 内部类 NotificationListenerWrapper 监听通知消息, 在收到消息之后就在里面解析消息,并创建视图了。

    protected class NotificationListenerWrapper extends INotificationListener.Stub {

      @Override
      public void onNotificationPosted(IStatusBarNotificationHolder sbnHolder,
              NotificationRankingUpdate update) {
          StatusBarNotification sbn;
          try {
              sbn = sbnHolder.get();
          } catch (RemoteException e) {
              Log.w(TAG, "onNotificationPosted: Error receiving StatusBarNotification", e);
              return;
          }
    
          try {
              // convert icon metadata to legacy format for older clients
              createLegacyIconExtras(sbn.getNotification());
              // 创建视图
              maybePopulateRemoteViews(sbn.getNotification());
    
              maybePopulatePeople(sbn.getNotification());
          } catch (IllegalArgumentException e) {
              // warn and drop corrupt notification
              Log.w(TAG, "onNotificationPosted: can't rebuild notification from " +
                      sbn.getPackageName());
              sbn = null;
          }
    
          // ... 省略代码
    
      }
    
      @Override
      public void onNotificationRemoved(IStatusBarNotificationHolder sbnHolder,
              NotificationRankingUpdate update, NotificationStats stats, int reason) {
          StatusBarNotification sbn;
          //... 省略代码
    
      }
    

    }

    在 maybePopulateRemoteViews 这个方法中会去检查布局是否要加载, 其实我们比较好奇的是布局资源在应用进程中,
    SystemUI 如何加载远程进程的布局资源?

    有两个关键的信息: 包名、布局ID。知道了包名 SystemUI 进程是有权限创建对应包名的上下文对象的,进而可以拿到对应应用的
    资源管理器, 然后就可以加载布局资源创建对象了。 maybePopulateRemoteViews 方法跟踪下去, 会走到 RemoteViews 的

    private View inflateView(Context context, RemoteViews rv, ViewGroup parent) {
    // RemoteViews may be built by an application installed in another
    // user. So build a context that loads resources from that user but
    // still returns the current users userId so settings like data / time formats
    // are loaded without requiring cross user persmissions.
    final Context contextForResources = getContextForResources(context);
    Context inflationContext = new RemoteViewsContextWrapper(context, contextForResources);

     // If mApplyThemeResId is not given, Theme.DeviceDefault will be used.
     if (mApplyThemeResId != 0) {
         inflationContext = new ContextThemeWrapper(inflationContext, mApplyThemeResId);
     }
     LayoutInflater inflater = (LayoutInflater)
             context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    
     // Clone inflater so we load resources from correct context and
     // we don't add a filter to the static version returned by getSystemService.
     inflater = inflater.cloneInContext(inflationContext);
     inflater.setFilter(this);
     View v = inflater.inflate(rv.getLayoutId(), parent, false);
     v.setTagInternal(R.id.widget_frame, rv.getLayoutId());
     return v;
    

    }

    其中 getContextForResources 中的 context 对象就是通过应用包名创建的上下文对象,创建过程:

    private static ApplicationInfo getApplicationInfo(String packageName, int userId) {
    if (packageName == null) {
    return null;
    }

      // Get the application for the passed in package and user.
      Application application = ActivityThread.currentApplication();
      if (application == null) {
          throw new IllegalStateException("Cannot create remote views out of an aplication.");
      }
    
      ApplicationInfo applicationInfo = application.getApplicationInfo();
      if (UserHandle.getUserId(applicationInfo.uid) != userId
              || !applicationInfo.packageName.equals(packageName)) {
          try {
              Context context = application.getBaseContext().createPackageContextAsUser(
                      packageName, 0, new UserHandle(userId));
              applicationInfo = context.getApplicationInfo();
          } catch (NameNotFoundException nnfe) {
              throw new IllegalArgumentException("No such package " + packageName);
          }
      }
    
      return applicationInfo;
    

    }

    只有 SystemUI 才能接收通知吗?

    答案是否定的, 只要有权限注册通知监听的应用都可以。 具体权限是:
    只要应用有这个权限就可以注册通知监听了, 这个权限只有系统应用才能申请, 也就是说,只要是系统应用都可以监听并显示通知的。 可以写一个简单的 demo 测试一下:

一、 申请权限

二、 在布局中定义一个容器来装远程通知视图

  ...
 <FrameLayout
     android:layout_width="match_parent"
     android:layout_height="92px"
     android:id="@+id/notification">

 </FrameLayout>
 ...

三、注册监听并处理通知显示逻辑。

  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    final ViewGroup notificationContainer = findViewById(R.id.notification);
    NotificationListenerService listenerService = new NotificationListenerService() {
        @SuppressLint("LongLogTag")
        @Override
        public void onNotificationPosted(StatusBarNotification sbn) {
            super.onNotificationPosted(sbn);
            Log.d("NotificationListenerService", "onNotificationPosted" + sbn);
            if (sbn.getNotification().contentView != null) {
                View view =  sbn.getNotification().contentView.apply(MainActivity.this, null);
                notificationContainer.addView(view);
                view.setVisibility(View.VISIBLE);
                Log.d("NotificationListenerService", "add contentView");
            }

            if (sbn.getNotification().bigContentView != null) {
                View view =  sbn.getNotification().bigContentView.apply(MainActivity.this, null);
                notificationContainer.addView(view);
                view.setVisibility(View.VISIBLE);
                Log.d("NotificationListenerService", "add bigContentView");
            }

            if (sbn.getNotification().headsUpContentView != null) {
                sbn.getNotification().headsUpContentView.apply(MainActivity.this, null);
                Log.d("NotificationListenerService", "add headsUpContentView");
            }

        }
        @SuppressLint("LongLogTag")
        @Override
        public void onNotificationRemoved(StatusBarNotification sbn) {
            super.onNotificationRemoved(sbn);
            Log.d("NotificationListenerService", "onNotificationRemoved" + sbn);
        }

        @SuppressLint("LongLogTag")
        @Override
        public void onListenerConnected() {
            super.onListenerConnected();
            Log.d("NotificationListenerService", "onNotificationRemoved");
        }

        @Override
        public void onListenerDisconnected() {
            super.onListenerDisconnected();
        }
    };

    // 调用注册方法 registerAsSystemService 不是公开的 API 反射

    try {
        Method method =
                NotificationListenerService.class.getMethod("registerAsSystemService", Context.class, ComponentName.class, int.class);

        method.setAccessible(true);
        method.invoke(listenerService, this,
                new ComponentName(getPackageName(), getClass().getCanonicalName()),
                -1);
    } catch (NoSuchMethodException e) {
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    } catch (InvocationTargetException e) {
        e.printStackTrace();
    }
}    

运行起来后,注册成功, 然后任意应用发通知, 这里就能显示出来了。

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