利用Handler来更新android的UI

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

newThread(newRunnable(){
publicvoidrun(){
myView.invalidate();
}
}).start();

 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，圆向右移动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

packagecom.ray.handler;
importandroid.content.Context;
importandroid.graphics.Canvas;
importandroid.graphics.Color;
importandroid.graphics.Paint;
importandroid.graphics.Point;
importandroid.graphics.drawable.Drawable;
importandroid.view.View;
publicclassBounceViewextendsView{
floatx=40;
publicBounceView(Contextcontext){
super(context);
}
@Override
protectedvoidonDraw(Canvascanvas){
x+=10;
PaintmPaint=newPaint();
mPaint.setAntiAlias(true);
mPaint.setColor(Color.GREEN);
canvas.drawCircle(x,40,40,mPaint);
}
}

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

packagecom.ray.handler;
importandroid.app.Activity;
importandroid.content.Context;
importandroid.graphics.Canvas;
importandroid.graphics.Color;
importandroid.graphics.Paint;
importandroid.os.Bundle;
importandroid.os.Handler;
importandroid.os.Message;
importandroid.view.View;
importandroid.view.Window;
publicclassTestHandlerextendsActivity{
protectedstaticfinalintGUIUPDATEIDENTIFIER=0x101;
ThreadmyRefreshThread=null;
BounceViewmyBounceView=null;
HandlermyHandler=newHandler(){
publicvoidhandleMessage(Messagemsg){
switch(msg.what){
caseTestHandler.GUIUPDATEIDENTIFIER:
myBounceView.invalidate();
break;
}
super.handleMessage(msg);
}
};
publicvoidonCreate(BundlesavedInstanceState){
super.onCreate(savedInstanceState);
this.requestWindowFeature(Window.FEATURE_NO_TITLE);
this.myBounceView=newBounceView(this);
this.setContentView(this.myBounceView);
newThread(newmyThread()).start();
}
classmyThreadimplementsRunnable{
publicvoidrun(){
while(!Thread.currentThread().isInterrupted()){
Messagemessage=newMessage();
message.what=TestHandler.GUIUPDATEIDENTIFIER;
TestHandler.this.myHandler.sendMessage(message);
try{
Thread.sleep(100);
}catch(InterruptedExceptione){
Thread.currentThread().interrupt();
}
}
}
}
}

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