Android：后台线程可能会阻塞，直到UI线程完成操作？

Question

后台线程是否可能将消息排入主UI线程的处理程序并阻塞，直到该消息已被服务？

对此的上下文是，我希望我的远程服务将每个已发布的操作从其主UI线程中取代，而不是从其接收到IPC请求的线程池线程。

Answer 1

这应该做你所需要的。它使用已知对象notify()和wait()来使该方法本质上同步。 run()中的任何内容都将在UI线程上运行，并在完成后将控制权返回doSomething()。这当然会让调用线程进入睡眠状态。

public void doSomething(MyObject thing) { 
    String sync = ""; 
    class DoInBackground implements Runnable { 
     MyObject thing; 
     String sync; 

     public DoInBackground(MyObject thing, String sync) { 
      this.thing = thing; 
      this.sync = sync; 
     } 

     @Override 
     public void run() { 
      synchronized (sync) { 
       methodToDoSomething(thing); //does in background 
       sync.notify(); // alerts previous thread to wake 
      } 
     } 
    } 

    DoInBackground down = new DoInBackground(thing, sync); 
    synchronized (sync) { 
     try { 
      Activity activity = getFromSomewhere(); 
      activity.runOnUiThread(down); 
      sync.wait(); //Blocks until task is completed 
     } catch (InterruptedException e) { 
      Log.e("PlaylistControl", "Error in up vote", e); 
     } 
    } 
}