利用Handler回更新android的UI(1)

利用Handler来更新android的UI(1)

刚刚开始接触android线程编程的时候，习惯好像java一样，试图用下面的代码解决问题

new Thread( new Runnable() {??
??? public void run() {??
???????? myView.invalidate();?
???? }?????????
}).start();??


然而发现这样是不行的，因为它违背了单线程模型：
Android UI操作并不是线程安全的并且这些操作必须在UI线程中执行。查阅了文档和apidemo后，发觉常用的方法是利用Handler来实现UI线程的更新的。
下面代码的功能很简单：画一个圆出来，每隔0.1秒，圆向10移动10个像素。但可以清楚展示利用Handler更新UI的流程。


首先创建简单的View,代码如下：

package com.ray.handler;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Point;
import android.graphics.drawable.Drawable;
import android.view.View;

public class BounceView extends View {
??? float x = 40;
???
??? public BounceView(Context context) {
???????? super(context);
??? }

??? @Override
??? protected void onDraw(Canvas canvas) {
??? x+=10;
??? Paint mPaint = new Paint();
??? mPaint.setAntiAlias(true);
??? mPaint.setColor(Color.GREEN);
??? canvas.drawCircle(x, 40, 40, mPaint);
??? }
}

创建Activity，代码如下：

package com.ray.handler;

import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.view.Window;

public class TestHandler extends Activity {
???? protected static final int GUIUPDATEIDENTIFIER = 0x101;

???? Thread myRefreshThread = null;
???? BounceView myBounceView = null;

???? Handler myHandler = new Handler() {
????????? public void handleMessage(Message msg) {
?????????????? switch (msg.what) {
??????????????????? case TestHandler.GUIUPDATEIDENTIFIER:
???????????????????????? myBounceView.invalidate();
???????????????????????? break;
?????????????? }
?????????????? super.handleMessage(msg);
????????? }
???? };
???? public void onCreate(Bundle savedInstanceState) {
????????? super.onCreate(savedInstanceState);
????????? this.requestWindowFeature(Window.FEATURE_NO_TITLE);

????????? this.myBounceView = new BounceView(this);
????????? this.setContentView(this.myBounceView);
????????? new Thread(new myThread()).start();
???? }

???? class myThread implements Runnable {
????????? public void run() {
?????????????? while (!Thread.currentThread().isInterrupted()) {?
????????????????????
??????????????????? Message message = new Message();
??????????????????? message.what = TestHandler.GUIUPDATEIDENTIFIER;
???????????????????
??????????????????? TestHandler.this.myHandler.sendMessage(message);
??????????????????? try {
???????????????????????? Thread.sleep(100);?
??????????????????? } catch (InterruptedException e) {
???????????????????????? Thread.currentThread().interrupt();
??????????????????? }
?????????????? }
????????? }
???? }
}