android Can't create handler inside thread that has not called Looper.prepare()

在android 线程中出现该错误

解决办法：

Handler handler = new Handler(){

@Override
public void handleMessage(Message msg) {
if(msg.what == 3){
Toast.makeText(DownloadService.this, "这里设置弹出的信息", 2000).show();
}
}

};

class MyThread implements Runnable{

@Override
public void run() {

Message msg = new Message();
msg.what = 3;
handler.sendMessage(msg);
}

}