app在启动时会产生一个进程和一个线程,线程是主线程,又叫UI线程,更新UI元素必须要在UI线程中更新,否则会报错。
在UI线程中有消息队列,子线程sendMessage到MQ中,looper类取出队列中的消息由UI线程中的Handler的handleMessage方法处理。
public class HandlerTestActivity extends Activity { private TextView tv; private static final int UPDATE = 0; private Handler handler = new Handler() { @Override public void handleMessage(Message msg) { // TODO 接收消息并且去更新UI线程上的控件内容 if (msg.what == UPDATE) { // Bundle b = msg.getData(); // tv.setText(b.getString("num")); tv.setText(String.valueOf(msg.obj)); } super.handleMessage(msg); } }; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); tv = (TextView) findViewById(R.id.tv); new Thread() { @Override public void run() { // TODO 子线程中通过handler发送消息给handler接收,由handler去更新TextView的值 try { for (int i = 0; i < 100; i++) { Thread.sleep(500); Message msg = new Message(); msg.what = UPDATE; // Bundle b = new Bundle(); // b.putString("num", "更新后的值:" + i); // msg.setData(b); msg.obj = "更新后的值:" + i; handler.sendMessage(msg); } } catch (InterruptedException e) { e.printStackTrace(); } } }.start(); } }