利用Handler来更新android的UI

原贴链接:http://rayleung.javaeye.com/blog/411860

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

Java代码
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：

Java代码
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：

Java代码
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();
}
}
}
}
}

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