Android SurfaceView

今天介绍一下SurfaceView的用法，SurfaceView一般与SurfaceHolder结合使用，SurfaceHolder用于向与之关联的SurfaceView上绘图，调用SurfaceView的getHolder()方法即可获取SurfaceView关联的SurfaceHolder。

SurfaceHolder提供一下几个方法来获取Canvas对象：

Canvas lockCanvas()：锁定整个SurfaceView对象，获取该Surface上的Canvas。

Canvas lockCanvas(Rect dirty)：锁定SurfaceView上Rect划分的区域，获取该Surface上的Canvas。

当通过lockCanvas获取指定SurfaceView上的Canvas之后，接下来程序就可以调用Canvas进行绘图，绘图完成后，调用一下方法来释放绘图、提交所绘制的图形：

unlockCanvasAndPost(canvas)。

下面直接上个实例：

 public class SurfaceViewTest extends Activity
 {
     // SurfaceHolder负责维护SurfaceView上绘制的内容
     private SurfaceHolder holder;
     private Paint paint;
     @Override
     public void onCreate(Bundle savedInstanceState)
     {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.main);
         paint = new Paint();
         SurfaceView surface = (SurfaceView) findViewById(R.id.show);
         // 初始化SurfaceHolder对象
         holder = surface.getHolder();
         holder.addCallback(new Callback()
         {
             @Override
             public void surfaceChanged(SurfaceHolder arg0, int arg1, int arg2,
                 int arg3)
             {
             }

             @Override
             public void surfaceCreated(SurfaceHolder holder)
             {
                 // 锁定整个SurfaceView
                 Canvas canvas = holder.lockCanvas();
                 // 绘制背景
                 Bitmap back = BitmapFactory.decodeResource(
                     SurfaceViewTest.this.getResources(), R.drawable.sun);
                 //绘制背景
                 canvas.drawBitmap(back, 0, 0, null);
                 // 绘制完成，释放画布，提交修改
                 holder.unlockCanvasAndPost(canvas);
                 //重新锁一次，"持久化"上次所绘制的内容
                 holder.lockCanvas(new Rect(0, 0, 0, 0));
                 holder.unlockCanvasAndPost(canvas);
             }

             @Override
             public void surfaceDestroyed(SurfaceHolder holder)
             {
             }
         });
         //为surface的触摸事件绑定监听器
         surface.setOnTouchListener(new OnTouchListener()
         {
             @Override
             public boolean onTouch(View source, MotionEvent event)
             {
                 // 只处理按下事件
                 if (event.getAction() == MotionEvent.ACTION_DOWN)
                 {
                     int cx = (int) event.getX();
                     int cy = (int) event.getY();
                     // 锁定SurfaceView的局部区域，只更新局部内容
                     Canvas canvas = holder.lockCanvas(new Rect(cx - 50,
                         cy - 50, cx + 50, cy + 50));
                     // 保存canvas的当前状态
                     canvas.save();
                     // 旋转画布
                     canvas.rotate(30, cx, cy);
                     paint.setColor(Color.RED);
                     // 绘制红色方块
                     canvas.drawRect(cx - 40, cy - 40, cx, cy, paint);
                     // 恢复Canvas之前的保存状态
                     canvas.restore();
                     paint.setColor(Color.GREEN);
                     // 绘制绿色方块
                     canvas.drawRect(cx, cy, cx + 40, cy + 40, paint);
                     // 绘制完成，释放画布，提交修改
                     holder.unlockCanvasAndPost(canvas);
                 }
                 return false;
             }
         });
     }
 }