SurfaceView应用浅析

SurfaceView在安卓的游戏开发，动画和图象处理中应用用比较多，也是提升程序性能，提高用户体验的一个方法。

SurfaceView不能直接使用，需要使用时需要基于他派生出我们自己的类，并导出SurfaceHolder.Callback接口并实现。 SurfaceView继承于视图类(View)，能够实现线程绘图主要是因为其内部包含一个专门用于绘制的Surface。人们通过 getHolder()获得Surface的句柄，然后通过SurfaceHolder接口的callback来使用他。SurfaceHolder的使用周期与surfaceview有关，surfaceview可见时，surface被创建；surfaceview不可见时，surface被销毁，且在surfaceview不可见之前。这样设计大概是基于节省资源考虑。surfaceview的核心提供了两个线程：UI线程和渲染线程。所有 SurfaceView和SurfaceHolder.Callback的方法都应该在UI线程里调用，一般来说就是应用程序主线程。渲染线程所要访问的各种变量应该作同步处理。由于surface可能被销毁，它只在SurfaceHolder.Callback.surfaceCreated()和 SurfaceHolder.Callback.surfaceDestroyed()之间有效，所以要确保渲染线程访问的是合法有效的surface。而我们的一些资源变量初始化和释放也尽量在这两个线方法之中。

SurfaceHolder在android说明文档中定义如下：

// 编译自SurfaceHolder.java （版本 1.5：49.0，无超级位）

public abstract static interfaceandroid.view.SurfaceHolder$Callback {

// 方法描述符 #4(Landroid/view/SurfaceHolder;)V

public abstractvoidsurfaceCreated(android.view.SurfaceHolder arg0);

// 方法描述符#6(Landroid/view/SurfaceHolder;III)V

public abstractvoidsurfaceChanged(android.view.SurfaceHolder arg0, int arg1, int arg2, intarg3);

// 方法描述符 #4(Landroid/view/SurfaceHolder;)V

public abstractvoidsurfaceDestroyed(android.view.SurfaceHolder arg0);

内部类：

[内部类信息：#1android/view/SurfaceHolder$Callback，外部类信息：#10android/view/SurfaceHolder

内部名： #12Callback，访问标志：1545 public abstract static]

}

调用SurfaceHolder需要重载这三个方法，然后通过lockCanvas方法获得画布绘图，绘结束后使用unlockCanvasAndPost提交给前台窗口刷新。流程是先获得SurfaceHolder，然后添加回调，实现三个接口，最后在lockCanvas和unlockCanvasAndPost之间实现代码：

一个简单的调用例子如下：

import android.app.Activity;

import android.content.Context;

import android.graphics.Canvas;

import android.graphics.Color;

import android.graphics.Paint;

import android.graphics.RectF;

import android.os.Bundle;

import android.view.SurfaceHolder;

import android.view.SurfaceView;

public class Test extends Activity {

 public void onCreate(Bundle savedInstanceState) {

 super.onCreate(savedInstanceState);

 setContentView(new MyView(this));

//内部类

 class MyView extends SurfaceView implements SurfaceHolder.Callback{

  SurfaceHolder holder;

 public MyView(Context context) {

 super(context);

 holder = this.getHolder();//获取holder

 holder.addCallback(this);

 //setFocusable(true);

 @Override

 public void surfaceChanged(SurfaceHolder holder, int format, int width,

 int height) {

 @Override

 public void surfaceCreated(SurfaceHolder holder) {

 new Thread(new MyThread()).start();

 @Override

 public void surfaceDestroyed(SurfaceHolder holder) {

 //内部类的内部类

 class MyThread implements Runnable{

 @Override

 public void run() {

 Canvas canvas = holder.lockCanvas(null);//获取画布

 Paint mPaint = new Paint();

 mPaint.setColor(Color.BLUE);

 canvas.drawRect(new RectF(40,60,80,80), mPaint);

 holder.unlockCanvasAndPost(canvas);//解锁画布，提交画好的图像

上面例子取自摘自http://www.iteye.com/topic/420410，只是一个简单的调用，但用来学习却是最容易理解的。下面是我写的一个例子，使用SurfaceView作一些简单的动画。动画是在窗口显示5*8个不断放大缩小的实心圆，图形如下：

代码如下：

import android.content.Context;

import android.graphics.Bitmap;

import android.graphics.Canvas;

import android.graphics.Color;

import android.graphics.Paint;

import android.graphics.Paint.Style;

import android.graphics.drawable.BitmapDrawable;

import android.view.SurfaceHolder;

import android.view.SurfaceView;

import android.view.KeyEvent;

import android.view.MotionEvent;

import android.view.SurfaceHolder.Callback;

public class MySurfaceView extends SurfaceView implements Runnable, Callback {

 private SurfaceHolder mHolder; // 用于控制SurfaceView

 private Thread t; // 声明一条线程

 private volatile boolean flag; // 线程运行的标识，用于控制线程

 private Canvas mCanvas; // 声明一张画布

 private Paint p; // 声明一支画笔

 float m_circle_r = 10;

 public MySurfaceView(Context context) {

 super(context);

 mHolder = getHolder(); // 获得SurfaceHolder对象

 mHolder.addCallback(this); // 为SurfaceView添加状态监听

 p = new Paint(); // 创建一个画笔对象

 p.setColor(Color.WHITE); // 设置画笔的颜色为白色

 setFocusable(true); // 设置焦点

/**

  * 当SurfaceView创建的时候，调用此函数

*/

 @Override

 public void surfaceCreated(SurfaceHolder holder) {

 t = new Thread(this); // 创建一个线程对象

 flag = true; // 把线程运行的标识设置成true

 t.start(); // 启动线程

/**

  * 当SurfaceView的视图发生改变的时候，调用此函数

*/

 @Override

 public void surfaceChanged(SurfaceHolder holder, int format, int width,

 int height) {

/**

  * 当SurfaceView销毁的时候，调用此函数

*/

 @Override

 public void surfaceDestroyed(SurfaceHolder holder) {

 flag = false; // 把线程运行的标识设置成false

 mHolder.removeCallback(this);

/**

  * 当屏幕被触摸时调用

*/

 @Override

 public boolean onTouchEvent(MotionEvent event) {

 return true;

/**

  * 当用户按键时调用

*/

 @Override

 public boolean onKeyDown(int keyCode, KeyEvent event) {

 if (keyCode == KeyEvent.KEYCODE_DPAD_UP) {

 return super.onKeyDown(keyCode, event);

 @Override

 public boolean onKeyUp(int keyCode, KeyEvent event) {

 surfaceDestroyed(mHolder);

 return super.onKeyDown(keyCode, event);

 @Override

 public void run() {

 while (flag) {

 try {

 synchronized (mHolder) {

 Thread.sleep(100); // 让线程休息1000毫秒

 Draw(); // 调用自定义画画方法

 } catch (InterruptedException e) {

 e.printStackTrace();

 } finally {

 if (mCanvas != null) {

 // mHolder.unlockCanvasAndPost(mCanvas);//结束锁定画图，并提交改变。

/**

  * 自定义一个方法，在画布上画一个圆

*/

 protected void Draw() {

 mCanvas = mHolder.lockCanvas(); // 获得画布对象，开始对画布画画

 if (mCanvas != null) {

 Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);

 paint.setColor(Color.BLUE);

 paint.setStrokeWidth(10);

 paint.setStyle(Style.FILL);

 if (m_circle_r >= (getWidth() / 10)) {

 m_circle_r = 0;

 } else {

 m_circle_r++;

 Bitmap pic = ((BitmapDrawable) getResources().getDrawable(

 R.drawable.qq)).getBitmap();

 mCanvas.drawBitmap(pic, 0, 0, paint);

 for (int i = 0; i < 5; i++)

 for (int j = 0; j < 8; j++)

 mCanvas.drawCircle(

 (getWidth() / 5) * i + (getWidth() / 10),

 (getHeight() / 8) * j + (getHeight() / 16),

 m_circle_r, paint);

 mHolder.unlockCanvasAndPost(mCanvas); // 完成画画，把画布显示在屏幕上

然后在Activity的create方法中调用就可以了：

 // setContentView(R.layout.main);

// 隐藏状态栏

 this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,

 WindowManager.LayoutParams.FLAG_FULLSCREEN);

 // 把Activity的标题去掉

 requestWindowFeature(Window.FEATURE_NO_TITLE);

 // 设置布局

 this.setContentView(new MySurfaceView(this));

这个动画也可以不使用SurfaceView直接在view里实现，这里使用Timer实现，代码如下：

import java.util.Timer;

import java.util.TimerTask;

import android.app.Activity;

import android.content.Context;

import android.graphics.Bitmap;

import android.graphics.Canvas;

import android.graphics.Color;

import android.graphics.Paint;

import android.graphics.Paint.Style;

import android.graphics.drawable.BitmapDrawable;

import android.os.Bundle;

import android.view.View;

public class TestDoubleActivity extends Activity {

 MyView mv;

 float m_circle_r = 10;

 /** Called when the activity is first created. */

 @Override

 public void onCreate(Bundle savedInstanceState) {

 super.onCreate(savedInstanceState);

 //setContentView(R.layout.main);

 mv = new MyView(this);

 setContentView(mv);

 Timer timer = new Timer();

timer.scheduleAtFixedRate(new MyTask(), 1, 100);

 public class MyView extends View {

 MyView(Context context) {

 super(context);

 @Override

 protected void onDraw(Canvas canvas) {

 // TODO Auto-generated method stub

 super.onDraw(canvas);

 Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);

  paint.setColor(Color.BLUE);

 paint.setStrokeWidth(10);

 paint.setStyle(Style.FILL);

  if (m_circle_r >= (getWidth()/10))

   m_circle_r = 0;

 else

 m_circle_r++;

  Bitmap pic = ((BitmapDrawable) getResources().getDrawable(R.drawable.qq)).getBitmap();

  canvas.drawBitmap(pic, 0, 0, paint);

 for (int i = 0; i < 5; i++)

 for (int j = 0; j < 8; j++)

 canvas.drawCircle((getWidth()/5)*i+(getWidth()/10), (getHeight()/8)*j+(getHeight()/16), m_circle_r, paint);

 private class MyTask extends TimerTask{

@Override

public void run() {

 mv.postInvalidate();

也能使用多线程实现，代码如下：

package com.test;

import android.app.Activity;

import android.content.Context;

import android.os.Bundle;

import java.lang.Thread;

import java.util.Random;

import android.view.View;

import android.graphics.Canvas;

import android.graphics.Color;

import android.graphics.Paint;

import android.graphics.Paint.Style;

import android.graphics.Path;

public class TestThreadActivity extends Activity {

 int c = Color.BLUE;

 MyThread myThread;

 volatile boolean bThreadRun = false;

 MyView mv;

 // 首先定义一个paint

 Paint paint = new Paint();

 Path m_path = new Path();

 volatile int ox = 0, oy = 0, nx = 100, ny = 200;

 final Random rand = new Random();

 /** Called when the activity is first created. */

 @Override

 public void onCreate(Bundle savedInstanceState) {

 super.onCreate(savedInstanceState);

 // setContentView(R.layout.main);

 mv = new MyView(this);

 setContentView(mv);

 @Override

 protected void onRestoreInstanceState(android.os.Bundle savedInstanceState) {

 super.onRestoreInstanceState(savedInstanceState);

 @Override

 protected void onSaveInstanceState(android.os.Bundle outState) {

 super.onSaveInstanceState(outState);

 @Override

 protected void onStart() {

 super.onStart();

 //myThread = new MyThread();

 //myThread.start();

 new Thread (new MyThread()).start();

 bThreadRun = true;

 @Override

 protected void onRestart() {

 super.onRestart();

 @Override

 protected void onResume() {

 super.onResume();

 @Override

 protected void onPause() {

 super.onPause();

 bThreadRun = false;

 // myThread.stop();

 @Override

 protected void onStop() {

 super.onStop();

 onPause();

 @Override

 protected void onDestroy() {

 super.onDestroy();

 // myThread.destroy();

 public class MyView extends View {

 MyView(Context context) {

 super(context);

 m_path.moveTo(ox, oy);

 @Override

 protected void onDraw(Canvas canvas) {

 // TODO Auto-generated method stub

 super.onDraw(canvas);

 // 绘制矩形区域-实心矩形

 // 设置颜色

 paint.setColor(c);

 paint.setStrokeWidth(10);

 // 设置样式-填充

 paint.setStyle(Style.STROKE);

 // 绘制一个矩形

 //canvas.drawRect(new Rect(0, 0, getWidth(), getHeight()), paint);

 nx = (int) (rand.nextFloat()*400);

 ny = (int) (rand.nextFloat()*800);

 m_path.lineTo(nx, ny);

 canvas.drawPath(m_path, paint);

 public class MyThread implements Runnable{

 // 线程的主要工作方法

 @Override

 public void run() {

 while (bThreadRun) {

 try {

 Thread.sleep(500);

 mv.postInvalidate();

 } catch(InterruptedException e){

使用TIMER，THREAD和surfaceview都能实现相同的效果，有什么区别呢，两者实现起来尽管那么像，但却一点都不一样，TIMER，THREAD都是在主UI线程里绘图的，遇到复杂情况，容易因为阻塞延迟超过5S而被系统干掉，surfaceview在自己的线程中处理，可以避免这个问题。最后一个例子中虽然使用了多线程，但并不能把绘图操作放入线程中处理，多线程也仅仅起到了与TIMER一样的作用，所以我们在许多UI设计中，肯定是离不开surfaceview的

参考资料：

http://www.cnblogs.com/xuling/archive/2011/06/06/android.html

http://www.iteye.com/topic/420410

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