getLooper() returns 启动 HandlerThread 后为空

Question

我有一个 class extends HandlerThread，它看起来像这样：

public class MyHandlerThread extends HandlerThread {

  private Object lock;

  //constructor
  public MyHandlerThread() {
     super(“MyHandlerThread”);
     lock = new Object();
  }

  public void prepare() {
     //starts the handler thread
     start();

     //Wait for thread starting
     Log.d(TAG, "wait for thread starting…");
     synchronized (lock) {
        try {
            lock.wait(5000);
        } catch (InterruptedException e) {
            Log.e(TAG, "Failed to wait for thread to start");
        }
     }

     //WHY getLooper() returns null here?
     if(getLooper() == null) {
         Log.d("GET LOOPER NULL!");
     }
  }

  @Override
  public void run() {
    Log.d("run() begin...");
    initializeSomeObjects()
    Log.d(“initialise objects done!”);

    //Notify that run() finished
    synchronized (lock) {
       lock.notify();
    }
    Log.d("run() end!”);
  }

}

正如你在上面看到的，prepare() 函数启动线程并等待 run() 完成，然后尝试获取 looper。

在另一个 class 中，我创建了一个 MyHandlerThread 的实例并启动它：

MyHandlerThread myThread = new MyHandlerThread();
myThread.prepare();

控制台中显示的日志：

wait for thread starting…
run() begin...
initialise objects done!
run() end!
GET LOOPER NULL!

为什么在prepare()函数中调用getLooper()returnsnull虽然线程已经启动了（run()是执行)?

Answer 1

HandlerThread Looper 在 HandlerThread#run() 中初始化。

如果您重写该方法而不调用 super.run()，则不会执行超类的初始化代码。

getLooper() returns 启动 HandlerThread 后为空

getLooper() returns null after started HandlerThread

android

android-handler

android-handlerthread

android-looper