如果我们想在子线程上创建Handler，通过直接new的出来是会报异常的比如：
[java]view plaincopy newThread(newRunnable(){publicvoidrun(){Handlerhandler=newHandler(){@OverridepublicvoidhandleMessage(Messagemsg){Toast.makeText(getApplicationContext(),"handlermsg",Toast.LENGTH_LONG).show();}};handler.sendEmptyMessage(1);};}).start();
会报错：
01-12 02:49:31.814: E/AndroidRuntime(2226): Java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
1.方法1（直接获取当前子线程的looper）
既然它说要Looper.prepare()，那我们就给他prepare()咯
[java]view plaincopy newThread(newRunnable(){publicvoidrun(){Looper.prepare();//此处获取到当前线程的Looper，并且prepare()Handlerhandler=newHandler(){@OverridepublicvoidhandleMessage(Messagemsg){Toast.makeText(getApplicationContext(),"handlermsg",Toast.LENGTH_LONG).show();}};handler.sendEmptyMessage(1);};}).start();
然后我们再运行，发现不报错了，但是handleMessage内的代码没执行，因为还差重要的一步，Looper.loop();最终代码是
[java]view plaincopy newThread(newRunnable(){publicvoidrun(){Looper.prepare();Handlerhandler=newHandler(){@OverridepublicvoidhandleMessage(Messagemsg){Toast.makeText(getApplicationContext(),"handlermsg",Toast.LENGTH_LONG).show();}};handler.sendEmptyMessage(1);Looper.loop();};}).start();
这样就OK了
2.方法2（获取主线程的looper，或者说是UI线程的looper）
这个方法简单粗暴，不过和上面的方法不一样的是，这个是通过主线程的looper来实现的
[java]view plaincopy newThread(newRunnable(){publicvoidrun(){Handlerhandler=newHandler(Looper.getMainLooper()){//区别在这！！！！@OverridepublicvoidhandleMessage(Messagemsg){Toast.makeText(getApplicationContext(),"handlermsg",Toast.LENGTH_LONG).show();}};handler.sendEmptyMessage(1);};}).start();
