为什么设置了HandlerThread的循环程序的Handler可以与UI对象交互？

Question

为什么此代码有效？

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

    Log.i("onCreate", Thread.currentThread().toString());
    textView = (TextView) findViewById(R.id.textView);
    imageView = (ImageView) findViewById(R.id.imageView);

    HandlerThread thread = new HandlerThread("myHandlerThread");
    thread.start();
    mUiHandler = new Handler(thread.getLooper());
    mUiHandler.post(new Runnable() {
        @Override
        public void run() {
            Log.i("Thread: ", Thread.currentThread().toString());
            Toast.makeText(getApplicationContext(), "Hello Cats!", Toast.LENGTH_SHORT).show();
            textView.setText("Hello Cats");
            imageView.setImageResource(R.mipmap.ic_launcher);
        }
    });

}

我从某处读取到可以与UI对象通信的唯一线程是UI线程，或者我错过了一些东西

我有一些研究，但尚未找到答案，请帮助，非常感谢你们。

这是我从日志中得到的

10-13 18:47:42.888 23841-23841/th.co.me.sampleapp I/onCreate: Thread[main,5,main] 10-13 18:47:42.891 23841-24041/th.co.me.sampleapp I/Thread:: Thread[myHandlerThread,5,main]

更新1

我尝试了来自@nshmura的这段代码，并且发生了错误，这现在让我感到困惑

   textView.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        HandlerThread thread = new HandlerThread("myHandlerThread");
        thread.start();
        mUiHandler = new Handler(thread.getLooper());
        mUiHandler.post(new Runnable() {
            @Override
            public void run() {
                Log.i("Thread: ", Thread.currentThread().toString());
                Toast.makeText(getApplicationContext(), "Hello Cats!", Toast.LENGTH_SHORT).show();
                textView.setText("Hello Cats");
                imageView.setImageResource(R.mipmap.ic_launcher);
            }
        });

    }
});

android.view.ViewRootImpl $ CalledFromWrongThreadException：只有创建视图层次结构的原始线程才能触摸其视图。

Answer 1

android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.异常android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views. 仅在以下情况下将被抛出：

1. 从非ui线程调用
2. 该呼叫需要更改布局。 例如，如果由于字符串太长而应扩展TextView的大小（宽度和高度）

因此，如果您的ui操作不会导致布局更改（创建或重新创建），则可能不会引发异常。

Answer 2

Handler对象向创建它的线程注册自己。 它提供了一个向该线程发送数据的通道。 例如，如果您在活动的onCreate（）方法中创建一个新的Handler实例，则可以使用该实例将数据发布到主线程。 可以通过Handler类发布的数据可以是Message或Runnable类的实例。

因此，根据下面的代码行，您的处理程序应属于HandlerThread。

mUiHandler = new Handler(thread.getLooper());

我了解OnCreate（）的一件事是主线程，但OnClick Listener是单独的类。 这意味着存在上下文差异。

例如：

// onCreate() we are writing like this
 Toast.makeText(this, "Hello Cats!", Toast.LENGTH_SHORT).show();
// but in Onclick method we are writing like this
 Toast.makeText(MainActivity.this, "Hello Cats!", Toast.LENGTH_SHORT).show();

Answer 3

像这样检查：

    textView.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            HandlerThread thread = new HandlerThread("myHandlerThread");
            thread.start();
            mUiHandler = new Handler(thread.getLooper());
            mUiHandler.post(new Runnable() {
                @Override
                public void run() {
                    Log.i("Thread: ", Thread.currentThread().toString());
                    Toast.makeText(getApplicationContext(), "Hello Cats!", Toast.LENGTH_SHORT).show();
                    textView.setText("Hello Cats");
                    imageView.setImageResource(R.mipmap.ic_launcher);
                }
            });

        }
    });

将会发生异常：

  android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
      at android.view.ViewRootImpl.checkThread(ViewRootImpl.java:6556)
      at android.view.ViewRootImpl.invalidateChildInParent(ViewRootImpl.java:942)
      at android.view.ViewGroup.invalidateChild(ViewGroup.java:5081)
      at android.view.View.invalidateInternal(View.java:12719)
      at android.view.View.invalidate(View.java:12683)
      at android.view.View.invalidate(View.java:12667)
      at android.widget.TextView.checkForRelayout(TextView.java:7156)
      at android.widget.TextView.setText(TextView.java:4347)
      at android.widget.TextView.setText(TextView.java:4204)
      at android.widget.TextView.setText(TextView.java:4179)

也许未在Activity.onCreate()调用ViewRootImpl.checkThread() Activity.onCreate()

Answer 4

试试这个代码

mHandler = new Handler();

new Thread(new Runnable() {
    @Override
    public void run () {
        // Perform long-running task here
        // (like audio buffering).
        // you may want to update some progress
        // bar every second, so use handler:
        mHandler.post(new Runnable() {
            @Override
            public void run () {
                // make operation on UI - on example
                // on progress bar.
            }
        });
    }
}).start();