Android surfaceview使用详解
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 interface android.view.SurfaceHolder$Callback {
// 方法描述符 #4(Landroid/view/SurfaceHolder;)V
public abstract voidsurfaceCreated(android.view.SurfaceHolder arg0);
// 方法描述符 #6(Landroid/view/SurfaceHolder;III)V
public abstract voidsurfaceChanged(android.view.SurfaceHolder arg0, int arg1, int arg2, int arg3);
// 方法描述符 #4(Landroid/view/SurfaceHolder;)V
public abstract voidsurfaceDestroyed(android.view.SurfaceHolder arg0);
内部类：
[内部类信息： #1android/view/SurfaceHolder$Callback， 外部类信息： #10android/view/SurfaceHolder
内部名： #12 Callback， 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