线程Handler

来源：互联网发布：口腔正畸知乎编辑：程序博客网时间：2024/05/16 00:40

这次学习一些线程方面的知识：

大家都知道，androidUI更新必须在主线程

下面用线程知识实现一个倒计时的效果：

下面这个如果把for循环里面的handler.sendEmptyMessage(-9);

换成下面的形式

Message message = new Message();

message.what = -9;
handler.sendMessage(message);

传递信息为什么不行？

必须使用handler.sendEmptyMessage(-9);才行谁知道为什么？

public class MainActivity extends Activity {private  MyView myView;private Button mybutton;private TextView mytextview;public static final int UPDATE_TEXT = 1;int i = 20;Message message = new Message();private Handler handler = new Handler(){public void handleMessage(Message msg) {switch (msg.what) {case -9:myView.setSweepValue(25);mybutton.setText(i+"");mytextview.setText(i+"");break;default:break;}}};@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);myView = (MyView) findViewById(R.id.myview);mybutton = (Button) findViewById(R.id.mybutton);mytextview = (TextView) findViewById(R.id.mytextview);mybutton.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubnew Thread(new Runnable() {@Overridepublic void run() {// TODO Auto-generated method stubfor(;i<=100;i+=10){if (i>=100) {break;}handler.sendEmptyMessage(-9);try {Thread.sleep(1000);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}}).start();}});}}

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