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;
            }
        });
    }
}