Android中SurfaceView学习

               SurfaceView和View的明显不同在于Surface不需要通过线程来更新视图，但在绘制之前必须使用lockCanvas方法锁定画布，并得 到画布，然后绘制，完成后用unlockCanvasAndPost方法解锁画布。SurfaceView类的事件处理和View一样。

             首先来看一个简单的框架。

绘制界面类：

package com.example.bonusball;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.RectF;
import android.util.AttributeSet;
import android.view.SurfaceHolder;
import android.view.SurfaceView;

public class CanvasView extends SurfaceView implements SurfaceHolder.Callback
{
private SurfaceHolder myHolder;
private Paint ballPaint; // Paint used to draw the cannonball
private int screenWidth; // width of the screen
private int screenHeight; // height of the screen
private int ballRadius;
private CanvasThread myThread;
//控制循环
private boolean isLoop;

public CanvasView(Context context) {
super(context);
// TODO Auto-generated constructor stub
myHolder=this.getHolder();
myHolder.addCallback(this);
ballPaint=new Paint();
ballPaint.setColor(Color.BLUE);
isLoop = true;
}

public void fireBall(float startX,float startY)
{
System.out.println("Fire");

}

@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width,
int height) {
// TODO Auto-generated method stub

}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh)
{
super.onSizeChanged(w, h, oldw, oldh);
screenWidth = w; // store the width
screenHeight = h; // store the height
ballRadius=w/10;
}

@Override
public void surfaceCreated(SurfaceHolder holder) {
// TODO Auto-generated method stub
myThread = new CanvasThread();
System.out.println("SurfaceCreated!");
myThread.start();

}

@Override
public void surfaceDestroyed(SurfaceHolder holder) {
// TODO Auto-generated method stub
// 停止循环
isLoop = false;
}
public void drawGameElements(Canvas canvas)
{
canvas.drawCircle(100, 100,ballRadius,ballPaint);

}
private class CanvasThread extends Thread
{
@Override
public void run()
{
while(true)
{
synchronized( myHolder )
{

Canvas canvas = myHolder.lockCanvas(null);//获取画布
drawGameElements(canvas);
myHolder.unlockCanvasAndPost(canvas);//解锁画布，提交画好的图像
//System.out.println("run");
}
}
}

}
}

事件处理 类：

package com.example.bonusball;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.view.GestureDetector;
import android.view.GestureDetector.SimpleOnGestureListener;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.widget.Toast;
public class BallActivity extends Activity {

private GestureDetector myGestureDetector;//监听手势
private CanvasView myCanvas;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
myCanvas=new CanvasView(this);
setContentView(myCanvas);
myGestureDetector = new GestureDetector(this, new MyGestureListener());

}
@Override
public boolean onTouchEvent(MotionEvent event)
{
return myGestureDetector.onTouchEvent(event);

}

private class MyGestureListener extends SimpleOnGestureListener
{
public boolean onDown(MotionEvent e1) {
Toast.makeText(getApplicationContext(), "onDown", Toast.LENGTH_SHORT).show();
return true;
}

@Override
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY)
{
System.out.println("Fling");
return true;
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_ball, menu);
return true;

}
}

解释几个 概念 ：

 callback接口:

 只要继承SurfaceView类并实现SurfaceHolder.Callback接口就可以实现一个自定义的SurfaceView 了，SurfaceHolder.Callback在底层的Surface状态发生变化的时候通知 View，SurfaceHolder.Callback具有如下的接口：

 surfaceCreated(SurfaceHolder
holder)：当Surface第一次创建后会立即调用该函数。程序可以在该函数中做些和绘制界面相关的初始化工作，一般情况下都是在另外的线程来绘制界面，所以不要在这个函数中绘制Surface。

 surfaceChanged(SurfaceHolder
holder, int format, int width,int height)：当Surface的状态（大小和格式）发生变化的时候会调用该函数，在surfaceCreated调用后该函数至少会被调用一次。

SurfaceHolder 类：

它是一个用于控制surface的接口，它提供了控制surface 的大小，格式，上面的像素，即监视其改变的。 

SurfaceView的getHolder()函数可以获取SurfaceHolder对象，Surface
就在SurfaceHolder对象内。虽然Surface保存了当前窗口的像素数据，但是在使用过程中是不直接和Surface打交道的，由SurfaceHolder的Canvas lockCanvas()或 则Canvas lockCanvas()函数来获取Canvas对象，通过在Canvas上绘制内容来修改Surface中的数据。如果Surface不可编辑或则尚未 创建调用该函数会返回null，在 unlockCanvas() 和 lockCanvas()中Surface的内容是不缓存的，所以需要完全重绘Surface的内容，为了提高效率只重绘变化的部分则可以调用
lockCanvas(Rect rect)函数来指定一个rect区域，这样该区域外的内容会缓存起来。在调用lockCanvas函数获取Canvas后，SurfaceView会获 取Surface的一个同步锁直到调用unlockCanvasAndPost(Canvas canvas)函数才释放该锁，这里的同步机制保证在Surface绘制过程中不会被改变（被摧毁、修改）。



最后来看一个复杂一些的例子 ，结合了之前的手势操作。
实现的效果是：在屏幕上进行Fling操作，在手滑动的方向上会产生一个运动的小球 ，速度 就是手势滑动的速度。
球的大小随机 ，颜色随机 ，碰到边界会反弹。
运行结果：



代码清单：
小球类，主要是设置几个属性，还有几个set，get方法。

package com.example.bonusball;

public class Ball {

private float posX;
private float posY;
private float velocityX;
private float velocityY;
private float radius;
private int color;
public Ball(int rgb,float r,float pX,float pY,float vX,float vY)
{
this.color=rgb;
this.radius=r;
this.posX=pX;
this.posY=pY;
this.velocityX=vX;
this.velocityY=vY;
}
public float getRadius()
{
return radius;
}
public int getColor()
{
return color;
}
public float getX()
{
return posX;
}
public float getY()
{
return posY;
}
public float getVX()
{
return velocityX;
}
public float getVY()
{
return velocityY;
}

public void setPosX(float newX)
{
this.posX=newX;
}
public void setPosY(float newY)
{
this.posY=newY;
}
public void setVX(float newVX)
{
this.velocityX=newVX;
}
public void setVY(float newVY)
{
this.velocityY=newVY;
}

}

主控类：

主要负责触控时间的监听。

package com.example.bonusball;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.view.GestureDetector;
import android.view.GestureDetector.SimpleOnGestureListener;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.widget.Toast;
public class BallActivity extends Activity {

private GestureDetector myGestureDetector;//监听手势
private CanvasView myCanvas;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
myCanvas=new CanvasView(this);
setContentView(myCanvas);
myGestureDetector = new GestureDetector(this, new MyGestureListener());

}
@Override
public boolean onTouchEvent(MotionEvent event)
{
return myGestureDetector.onTouchEvent(event);

}

private class MyGestureListener extends SimpleOnGestureListener
{
public boolean onDown(MotionEvent e1) {
// Toast.makeText(getApplicationContext(), "onDown", Toast.LENGTH_SHORT).show();
//myCanvas.fireBall(e1.getRawX(),e1.getRawY(),0,0);
return true;
}

@Override
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY)
{
System.out.println("Fling");
final int FLING_MIN_DISTANCE = 100, FLING_MIN_VELOCITY = 200;
if (Math.abs(e1.getX() - e2.getX()) > FLING_MIN_DISTANCE && Math.abs(velocityX) > FLING_MIN_VELOCITY)
myCanvas.fireBall(e1.getRawX(),e1.getRawY(),velocityX/4,velocityY/4);
return true;
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_ball, menu);
return true;

}
}

画板类：

负责图形的绘制。
package com.example.bonusball;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.CopyOnWriteArrayList;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.RectF;
import android.util.AttributeSet;
import android.view.SurfaceHolder;
import android.view.SurfaceView;

public class CanvasView extends SurfaceView implements SurfaceHolder.Callback
{
private SurfaceHolder myHolder;
private Paint ballPaint; // Paint used to draw the cannonball
private int screenWidth; // width of the screen
private int screenHeight; // height of the screen
private int maxBallRadius;
private CanvasThread myThread;
private List<Ball> ballList;
private Paint backgroundPaint;
private Random mRandom;
//控制循环
private boolean isLoop;

public CanvasView(Context context) {
super(context);
// TODO Auto-generated constructor stub
myHolder=this.getHolder();
myHolder.addCallback(this);
ballPaint=new Paint();

backgroundPaint = new Paint();
backgroundPaint.setColor(Color.BLACK);
isLoop = true;
ballList=new CopyOnWriteArrayList<Ball>();
mRandom=new Random();
}

public void fireBall(float startX,float startY,float velocityX,float velocityY)
{

int ranColor = 0xff000000 | mRandom.nextInt(0x00ffffff);
float randomRadius=mRandom.nextInt(maxBallRadius);
float tmpRadius=maxBallRadius/5.0>randomRadius?maxBallRadius:randomRadius;
ballList.add(new Ball(ranColor,tmpRadius,startX,startY,velocityX,velocityY));
System.out.println("Fire");
}

@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width,
int height) {
// TODO Auto-generated method stub

}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh)
{
super.onSizeChanged(w, h, oldw, oldh);
screenWidth = w; // store the width
screenHeight = h; // store the height
maxBallRadius=w/10;
}

@Override
public void surfaceCreated(SurfaceHolder holder) {
// TODO Auto-generated method stub
myThread = new CanvasThread();
System.out.println("SurfaceCreated!");
myThread.start();

}

@Override
public void surfaceDestroyed(SurfaceHolder holder) {
// TODO Auto-generated method stub
// 停止循环
isLoop = false;
}
public void drawGameElements(Canvas canvas)
{

canvas.drawRect(0, 0, canvas.getWidth(), canvas.getHeight(), backgroundPaint);
for(Ball b:ballList)
{
ballPaint.setColor(b.getColor());
canvas.drawCircle(b.getX(),b.getY(),b.getRadius(),ballPaint);
}
}

private void updatePositions(double elapsedTimeMS) {
// TODO Auto-generated method stub
float interval = (float) (elapsedTimeMS / 1000.0);
for(Ball b:ballList)
{
b.setPosX(b.getX()+b.getVX()*interval);
b.setPosY(b.getY()+b.getVY()*interval);
if (b.getX() + b.getRadius()> screenWidth )
{
b.setVX(-1*b.getVX());
//边界修复
b.setPosX(screenWidth-b.getRadius());
}
if(b.getX() - b.getRadius() < 0)
{
b.setVX(-1*b.getVX());
b.setPosX(b.getRadius());
}
if (b.getY() + b.getRadius()> screenHeight)
{
b.setVY(-1*b.getVY());
b.setPosY(screenHeight-b.getRadius());
}
if(b.getY() - b.getRadius() < 0)
{
b.setVY(-1*b.getVY());
b.setPosY(b.getRadius());
}
}

}

private class CanvasThread extends Thread
{
@Override
public void run()
{

Canvas canvas=null;
long previousFrameTime = System.currentTimeMillis();
while(isLoop)
{

try{
canvas = myHolder.lockCanvas(null);//获取画布
synchronized( myHolder )
{
canvas.drawColor(Color.BLACK);
long currentTime = System.currentTimeMillis();
double elapsedTimeMS = currentTime - previousFrameTime;
updatePositions(elapsedTimeMS); // update game state
drawGameElements(canvas);
previousFrameTime = currentTime; // update previous time
//System.out.println("run");
}
}
finally
{
if (canvas != null)
myHolder.unlockCanvasAndPost(canvas);//解锁画布，提交画好的图像
} // end finally
}
}

}
}


未解决问题一枚
理论上surfaceview是 带双缓冲的，但实际运行起来，图像还是有闪烁。
尝试写一个新的进程来处理图像的绘制，未果。