如何在子线程中创建Handler?

也许大家创建Handler都不陌生，但是如果要在子线程创建Handler，大家未必都能正确，

在子线程中创建handler，要确保子线程有Looper,UI线程默认包含Looper

我们需要用到一个特殊类 

HandlerThread

这个类可以轻松的创建子线程handler

创建步骤:

1: 创建一个HandlerThread，即创建一个包含Looper的线程

   HandlerThread的构造函数有两个

  public HandlerThread(String name) {
        super(name);
        mPriority = Process.THREAD_PRIORITY_DEFAULT;
    }
    
    /**
     * Constructs a HandlerThread.
     * @param name
     * @param priority The priority to run the thread at. The value supplied must be from 
     * {@link android.os.Process} and not from java.lang.Thread.
     */
    public HandlerThread(String name, int priority) {
        super(name);
        mPriority = priority;
    }

这里我们使用第一个就好:

HandlerThread handlerThread=new HandlerThread("xuan");

handlerThread.start();//创建HandlerThread后一定要记得start();

通过HandlerThread的getLooper方法可以获取Looper

Looper looper=handlerThread.getLooper();

通过Looper我们就可以创建子线程的handler了

Handlr handler=new Handler(looper);

通过该handler发送消息，就会在子线程执行;

提示:如果要handlerThread停止:handlerThread.quit();

完整测试代码:

  HandlerThread hanlerThread = new HandlerThread("子线程");
        hanlerThread.start();
        final Handler handler = new Handler(hanlerThread.getLooper()) {
            @Override
            public void handleMessage(Message msg) {
                super.handleMessage(msg);
                Log.d("----->", "线程:" + Thread.currentThread().getName());
            }
        };
        findViewById(R.id.bt).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                handler.sendEmptyMessage(100);
            }
        });

结果:

12-24 10:13:15.881 5024-5052/gitosctest.gitosc_studyproject D/----->: 线程:子线程

像在intentService(子线程)中,如果要回掉在UI线程怎么办呢?

 new Handler(getMainLooper()).post(new Runnable() {
                    @Override
                    public void run() {
                        // person.getName() Realm objects can only be accessed on the thread they were created.
                        Toast.makeText(getApplicationContext(), "Loaded Person from broadcast-receiver->intent-service: " + info, Toast.LENGTH_LONG).show();
                    }
                });