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

new
Thread(
new
Runnable() {

public

void
run() {

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);

}

}

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();

}

}

}

}

}