Java 从Android中的辅助线程调用主线程

Call Main thread from secondary thread in Android

提问by sajjoo

How to call Main thread from secondary thread in Android?

如何从Android中的辅助线程调用主线程？

采纳答案by thoredge

The simplest way is to call runOnUiThread(...) from your thread

最简单的方法是从你的线程调用 runOnUiThread(...)

activity.runOnUiThread(new Runnable() {
    public void run() {
        ... do your GUI stuff
    }
});

回答by Jesus Oliva

My recommendation to communicate threads in the same process is sending messages between those threads. It is very easy to manage this situation using Handlers:

我建议在同一进程中通信线程是在这些线程之间发送消息。使用处理程序很容易管理这种情况：

http://developer.android.com/reference/android/os/Handler.html

http://developer.android.com/reference/android/os/Handler.html

Example of use, from Android documentation, to handling expensive work out of the ui thread:

使用示例，来自 Android 文档，用于处理 ui 线程之外的昂贵工作：

public class MyActivity extends Activity {

    [ . . . ]
    // Need handler for callbacks to the UI thread
    final Handler mHandler = new Handler();

    // Create runnable for posting
    final Runnable mUpdateResults = new Runnable() {
        public void run() {
            updateResultsInUi();
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        [ . . . ]
    }

    protected void startLongRunningOperation() {

        // Fire off a thread to do some work that we shouldn't do directly in the UI thread
        Thread t = new Thread() {
            public void run() {
                mResults = doSomethingExpensive();
                mHandler.post(mUpdateResults);
            }
        };
        t.start();
    }

    private void updateResultsInUi() {

        // Back in the UI thread -- update our UI elements based on the data in mResults
        [ . . . ]
    }
}

回答by keyboardsurfer

You'll need a Handlerthat passes the information back to the main thread.

您需要Handler将信息传递回主线程。

回答by Tad

Also, it's good to remember that if you get your secondary thread through an AsyncTask, you have the option to call onProgressUpdate(), onPostExecute(), etc., to do work on the main thread.

此外，最好记住，如果您通过 AsyncTask 获取辅助线程，则可以选择调用onProgressUpdate()、 onPostExecute()等，以在主线程上工作。

回答by Ravindra babu

Sample code using HandlerThread

使用HandlerThread 的示例代码

public class MainActivity extends AppCompatActivity {

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

        final Handler responseHandler = new Handler(Looper.getMainLooper()){
            @Override
            public void handleMessage(Message msg) {
                //txtView.setText((String) msg.obj);
                Toast.makeText(MainActivity.this,
                        "Result from UIHandlerThread:"+(int)msg.obj,
                        Toast.LENGTH_LONG)
                        .show();
            }
        };

        HandlerThread handlerThread = new HandlerThread("UIHandlerThread"){
            public void run(){
                /* Add your business logic to pupulate attributes in Message
                   in place of sending Integer 5 as in example code */
                Integer a = 5;
                Message msg = new Message();
                msg.obj = a;
                responseHandler.sendMessage(msg);
                System.out.println(a);
            }
        };
        handlerThread.start();

    }

}

Explanation:

解释：

1. In above example, HandlerThreadpost a Messageon Handlerof UI Thread, which has been initialized with Looperof UI Thread.

   final Handler responseHandler = new Handler(Looper.getMainLooper())
   

2. responseHandler.sendMessage(msg);sends Messagefrom HandlerThreadto UI Thread Handler.

3. handleMessageprocesses Messagereceived on MessageQueueand shows a Toast on UI Thread.

1. 在上述示例中，HandlerThread发布一个Message关于HandlerUI线程，这已被初始化的LooperUI线程的。

   final Handler responseHandler = new Handler(Looper.getMainLooper())
   

2. responseHandler.sendMessage(msg);发送Message从HandlerThread到UI线程Handler。

3. handleMessage进程Message收到MessageQueue并在 UI 线程上显示 Toast。