View刷新

在Android的布局体系中，父View负责刷新、布局显示子View；而当子View需要刷新时，则是通知父View来完成。postinvaliate()可以在分线程刷新invaliate()只能在主线程中执行横竖屏切换的时候一定会刷新View1.不使用多线程和双缓冲     这种情况最简单了，一般只是希望在View发生改变时对UI进行重绘。你只需在Activity中显式地调用View对象中的invalidate()方法即可。系统会自动调用 View的onDraw()方法。

/**
* Invalidate the whole view. If the view is visible,
* {@link #onDraw(android.graphics.Canvas)} will be called at some point in
* the future.
* <p>
* This must be called from a UI thread. To call from a non-UI thread, call
* {@link #postInvalidate()}.
*/
public void invalidate() {
invalidate(true);
}

@Override
protected void onDraw(Canvas canvas) {
if (canvas instanceof HardwareCanvas) {
HardwareCanvas hwCanvas = (HardwareCanvas) canvas;
mView.mRecreateDisplayList = true;
RenderNode renderNode = mView.getDisplayList();
if (renderNode.isValid()) {
hwCanvas.insertReorderBarrier(); // enable shadow for this rendernode
hwCanvas.drawRenderNode(renderNode);
hwCanvas.insertInorderBarrier(); // re-disable reordering/shadows
}
}
}

2.使用多线程和不使用双缓冲     这种情况需要开启新的线程，新开的线程就不好访问View对象了。强行访问的话会报：android.view.ViewRoot$CalledFromWrongThreadException：Only the original thread that created a view hierarchy can touch its views.     这时候你需要创建一个继承了android.os.Handler的子类，并重写handleMessage(Message msg)方法。android.os.Handler是能发送和处理消息的，你需要在Activity中发出更新UI的消息，然后再你的Handler（可以使用匿名内部类）中处理消息（因为匿名内部类可以访问父类变量， 你可以直接调用View对象中的invalidate()方法 ）。也就是说：在新线程创建并发送一个Message，然后再主线程中捕获、处理该消息。

/**
* 要在Activity中开启一个用于更新的线程
* timeViewHandler 继承自Handler，用于处理和发送消息
* MSG_UPDATE 是自定义的一个int常量，用于区分消息类型，可自由取值。
*/
new Thread(new Runnable() {
@Override
public void run() {
while(true){
try {
timeViewHandler.sendMessage(Message.obtain(timeViewHandler, MSG_UPDATE));
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}).start();

/**
* Handler示例，用于刷新时间
*/
public class TimeViewHandler extends Handler {
private TextView timeView;

public TextView getTimeView() {
return timeView;
}

public void setTimeView(TextView timeView) {
this.timeView = timeView;
}

public TimeViewHandler(TextView timeView) {
super();
this.timeView = timeView;
}

@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case MSG_UPDATE:
timeView.setText(DateHelper.getNow("kk:mm:ss"));
timeView.invalidate();
break;
}
super.handleMessage(msg);
}

}

3.使用多线程和双缓冲

    Android中SurfaceView是View的子类，她同时也实现了双缓冲。也可以定义一个她的子类并实现SurfaceHolder.Callback接口。由于实现SurfaceHolder.Callback接口，新线程就不需要android.os.Handler帮忙了。SurfaceHolder中lockCanvas()方法可以锁定画布，绘制玩新的图像后调用unlockCanvasAndPost(canvas)解锁（显示），还是比较方便得。/*** SurfaceView使用示例，TouchDrawView主要完成屏幕的指尖绘画*/public class TouchDrawView extends SurfaceView implements SurfaceHolder.Callback{private SurfaceHolder holder;private TouchDrawListener listener;public TouchDrawListener getListener() {return listener;}public void setListener(TouchDrawListener listener) {this.listener = listener;}public TouchDrawView(Context context) {super(context);holder = getHolder();holder.addCallback(this);listener = new TouchDrawListener(holder);listener.setShape(TouchDrawListener.SHAPE_LINE);listener.setShape_style(TouchDrawListener.SHAPE_STYLE_FILL);this.setOnTouchListener(listener);//设置屏幕事件监听器this.setLongClickable(true);//不设置将无法捕捉onFling()事件setFocusable(true);//设置键盘焦点setFocusableInTouchMode(true);//设置触摸屏焦点}public TouchDrawView(Context context, AttributeSet as) {this(context);}@Overrideprotected void onDraw(Canvas canvas) {}@Overridepublic void surfaceChanged(SurfaceHolder holder, int format, int width,int height) {}@Overridepublic void surfaceCreated(SurfaceHolder holder) {//关键部分Canvas canvas = holder.lockCanvas(null);//获取画布canvas.drawColor(Color.WHITE);//白色背景holder.unlockCanvasAndPost(canvas);//解锁画布，提交画好的图像}@Overridepublic void surfaceDestroyed(SurfaceHolder holder) {}}

使用postInvalidate()刷新界面使用postInvalidate则比较简单，不需要handler，直接在线程中调用postInvalidate即可。

class GameThread implements Runnable {public void run() {while (!Thread.currentThread().isInterrupted()) {try {Thread.sleep(100);} catch (InterruptedException e) {Thread.currentThread().interrupt();}// 使用postInvalidate可以直接在线程中更新界面mGameView.postInvalidate();}}}