如何实现Android SurfaceView

SurfaceView是View的继承结构中一个比较特殊的子类，它的作用是提供一个第二线程来完成图形的绘制。因此应用程序不需要等待View的图形绘制，第二线程会异步完成图形的绘制。

SurfaceView实现的步骤：

继续SurfaceView并实现SurfaceHolder.Callback接口，该接口提供了SurfaceView创建、属性发生变化、销毁的时间点，那么你可以在适当的时间点完成具体的工作。
在SurfaceView初始化的时候调用SurfaceView.getHolder()方法获取一个SurfaceHolder，SurfaceHolder用于管理SurfaceView的工作过程。为了让SurfaceHolder起作用，必须为SurfaceHolder添加回调方法（即第一步实现的SurfaceHolder.Callback）：
Java代码
1. SurfaceHolder.addCallBack(SurfaceHolder.Callback);
在SurfaceView内创建第二线程的内部类（暂命名为SecondThread），它的主要任务是完成Canvas的图形绘制。为了能让SecondThread获得Canvas实例，必须给SecondThread传递在步骤二中获得的SurfaceHolder。现在就可以通过SurfaceHolder.lockCanvas()方法得到Canvas实例，并在Canvas上绘制图形。当图形绘制完成后，必须马上调用SurfaceHolder.unlockCanvasAndPost()为Canvas解锁，使其他线程可以使用该画布。

有几个注意点：

每一次通过SurfaceHolder获取的Canvas都会保持上一次绘制的状态。如果需要重新绘制图形，可以通过调用Canvas.drawColor()或Canvas.drawBitmap()来擦除上次遗留的图形。
并不一定只用第二线程来绘制图形，也可以开启第三，第四个线程来绘制图形。
注意线程安全。
不需要像View一样，调用invalidate()方法来指示图形的刷新。

SurfaceView的一个范例：

Java代码

package com.sin90lzc.android.sample;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.util.Log;
import android.view.KeyEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
public class CanvasView extends SurfaceView implements SurfaceHolder.Callback {
public static class Point {
private float x;
private float y;
public Point(float x, float y) {
this.x = x;
this.y = y;
}
public float getX() {
return x;
}
public void setX(float x) {
this.x = x;
}
public float getY() {
return y;
}
public void setY(float y) {
this.y = y;
}
public Point nextPoint(Orien o) {
float tempX = x;
float tempY = y;
switch (o) {
case UP:
tempY = y - LINE_LENGTH;
break;
case DOWN:
tempY = y + LINE_LENGTH;
break;
case LEFT:
tempX = x - LINE_LENGTH;
break;
case RIGHT:
tempX = x + LINE_LENGTH;
break;
case UNKNOWN:
break;
}
return new Point(tempX, tempY);
}
}
enum Orien {
UP, LEFT, DOWN, RIGHT, UNKNOWN
}
public static class DrawThread extends Thread {
private List<Point> points = Collections
.synchronizedList(new ArrayList<Point>());
private boolean mRun;
private Paint mPaint;
private Orien curOrien;
public synchronized void setRun(boolean run) {
this.mRun = run;
notifyAll();
}
public synchronized boolean getRun() {
while (!mRun) {
try {
wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
return mRun;
}
//当按上下左右键时，生成相应的点坐标
private synchronized boolean doKeyDown(int KeyCode, KeyEvent event) {
synchronized (holder) {
Point p = null;
switch (KeyCode) {
case KeyEvent.KEYCODE_DPAD_UP:
if (curOrien != Orien.DOWN) {
curOrien = Orien.UP;
p = curPoint.nextPoint(curOrien);
}
break;
case KeyEvent.KEYCODE_DPAD_DOWN:
if (curOrien != Orien.UP) {
curOrien = Orien.DOWN;
p = curPoint.nextPoint(curOrien);
}
break;
case KeyEvent.KEYCODE_DPAD_LEFT:
if (curOrien != Orien.RIGHT) {
curOrien = Orien.LEFT;
p = curPoint.nextPoint(curOrien);
}
break;
case KeyEvent.KEYCODE_DPAD_RIGHT:
if (curOrien != Orien.LEFT) {
curOrien = Orien.RIGHT;
p = curPoint.nextPoint(curOrien);
}
break;
default:
curOrien = Orien.UNKNOWN;
}
if (p != null) {
curPoint = p;
points.add(p);
setRun(true);
}
Log.i(LOG_TAG, curOrien.toString());
}
return true;
}
//当释放按键时，停止绘图
private synchronized boolean doKeyUp(int KeyCode, KeyEvent event) {
synchronized (holder) {
setRun(false);
curOrien = Orien.UNKNOWN;
}
return true;
}
SurfaceHolder holder;
private Point curPoint;
public DrawThread(SurfaceHolder holder) {
this.holder = holder;
mPaint = new Paint();
mPaint.setColor(Color.GREEN);
curPoint = new Point(50, 50);
points.add(curPoint);
}
public void resetPoint() {
}
private void doDraw(Canvas canvas) {
for (int i = 0; i + 1 < points.size(); i += 1) {
Point lp = points.get(i);
Point np = points.get(i + 1);
canvas.drawLine(lp.getX(), lp.getY(), np.getX(), np.getY(),
mPaint);
}
}
@Override
public void run() {
Canvas canvas = null;
while (getRun()) {
try {
canvas = holder.lockCanvas();
synchronized (holder) {
doDraw(canvas);
}
} finally {
holder.unlockCanvasAndPost(canvas);
setRun(false);
}
}
}
}
private DrawThread thread;
public static final String LOG_TAG = "CanvasView";
private static final int LINE_LENGTH = 30;
public CanvasView(Context context) {
super(context);
}
public CanvasView(Context context, AttributeSet attrs) {
super(context, attrs);
//SurfaceView由SurfaceHolder管理
SurfaceHolder holder = getHolder();
holder.addCallback(this);
thread = new DrawThread(holder);
thread.start();
}
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
return thread.doKeyDown(keyCode, event);
}
@Override
public boolean onKeyUp(int keyCode, KeyEvent event) {
return thread.doKeyUp(keyCode, event);
}
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width,
int height) {
Log.i(LOG_TAG, "surfaceChanged");
thread.resetPoint();
thread.setRun(true);
}
@Override
public void surfaceCreated(SurfaceHolder holder) {
Log.i(LOG_TAG, "surfaceCreated");
thread.resetPoint();
thread.setRun(true);
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
Log.i(LOG_TAG, "surfaceDestroyed");
thread.setRun(false);
}
}

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