Android—子线程更新UI问题（ java.lang.RuntimeException: Can't create handler inside thread that has not cal）

之前在子线程中显示一个UI操作，发生错误

 java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()

代码为：延时3秒后发出一个Toast信息

 new Thread(){
         public void run(){
             try {
                 Thread.sleep(2999);              
                 Toast.makeText(MainActivity.this, "请重新连接",Toast.LENGTH_LONG).show();
             } catch (InterruptedException e) { }
         }
     }.start();

这里明显在子线程进行UI更新，所以发生错误

解决：在子线程中发送一个message到Handle，让Handle更新线程

代码：

线程：

 new Thread(){
          public void run(){
              try {
                  Thread.sleep(2999);
                  mHandler.sendEmptyMessage(0);
              } catch (InterruptedException e) { }
          }
      }.start();

Handle写在onCreate()之外

Handler mHandler = new Handler() {
	        public void handleMessage(Message msg) {
	        	Toast.makeText(MainActivity.this, "请重新连接",Toast.LENGTH_LONG).show();
	            super.handleMessage(msg);
	        }
	    };