/////////继承SurfaceView 的类

public class PaintView extends SurfaceView implements Runnable,SurfaceHolder.Callback {

    private float mX;

    private float mY;

    private  Paint mPaint = null;

    private  Path mPath = null;

    // 线程结束标志位

    boolean mLoop = true;

    SurfaceHolder mSurfaceHolder = null;

   Canvas mCanvas;

 public PaintView(Context context, AttributeSet arr) {

        super(context , arr);

        mSurfaceHolder = this.getHolder();//获取holder

        mSurfaceHolder.addCallback(this);

        mSurfaceHolder.setFormat(PixelFormat.OPAQUE);//不透明

        //mSurfaceHolder.setFormat(PixelFormat.RGB_565);

        //mSurfaceHolder.setFormat(PixelFormat.RGBA_8888);

        this.setFocusable(true);

//        setZOrderOnTop(true);//放到最顶层

        mPaint = new Paint();

        mPath = new Path();

        mPaint.setAntiAlias(true);

        mPaint.setStyle(Style.STROKE);

        mPaint.setStrokeWidth(5);

        mPaint.setColor(mPaintColor);

        mPaint.setStrokeCap(Paint.Cap.ROUND);  //圆头

        mPaint.setDither(true);//消除拉动，使画面圓滑

        mPaint.setStrokeJoin(Paint.Join.ROUND); //结合方式，平滑

}

   @Override

    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {

        // TODO Auto-generated method stub

    }

    @Override

    public void surfaceCreated(SurfaceHolder holder) {

        // TODO Auto-generated method stub

        new Thread(this).start();//启动线程

    }

    @Override

    public void surfaceDestroyed(SurfaceHolder holder) {

        // TODO Auto-generated method stub

        mLoop = false; //结束线程

    }

    @Override

    public void run() {

        while (mLoop==true) {

                Draw();

            try {

                Thread.sleep(100);

            } catch (InterruptedException e) {

                e.printStackTrace();

            }

        }

    }

 // 画图

    private void Draw() {

        try{

        mCanvas = mSurfaceHolder.lockCanvas();

        mCanvas.drawPath(mPath, mPaint);  ////

        }catch (Exception e){

            }finally {

            if (mCanvas !=null) {

                mSurfaceHolder.unlockCanvasAndPost(mCanvas);

                }

            }

    }

   @Override

    public boolean onTouchEvent(MotionEvent event)

    {

        switch (event.getAction())

        {

            case MotionEvent.ACTION_DOWN:

                touchDown(event);

                 break;

            case MotionEvent.ACTION_MOVE:

                touchMove(event);

        }

        //更新绘制

        invalidate();

        return true;

    }

    //手指点下屏幕时调用

    private void touchDown(MotionEvent event)

    {

        //隐藏之前的绘制

//        mPath.reset();  //

        float x = event.getX();

        float y = event.getY();  

        mX = x;

        mY = y;

        //mPath绘制的绘制起点

        mPath.moveTo(x, y);

    }  

    //手指在屏幕上滑动时调用

    private void touchMove(MotionEvent event)

    {

        final float x = event.getX();

        final float y = event.getY();  

        final float previousX = mX;

        final float previousY = mY;  

        final float dx = Math.abs(x - previousX);

        final float dy = Math.abs(y - previousY);  

        //两点之间的距离大于等于3时，生成贝塞尔绘制曲线

        if (dx >= 3 || dy >= 3)

        {

            //设置贝塞尔曲线的操作点为起点和终点的一半

            float cX = (x + previousX) / 2;

            float cY = (y + previousY) / 2;  

            //二次贝塞尔，实现平滑曲线；previousX, previousY为操作点，cX, cY为终点

            mPath.quadTo(previousX, previousY, cX, cY);  

            //第二次运行时，第一次结束调用的坐标值将作为第二次调用的初始坐标值

            mX = x;

            mY = y;

        }

    }

////橡皮擦

   private void setEraser(){

        mPaint = new Paint();

        mPath = new Path();

        mPaint.setAntiAlias(true);

        mPaint.setStyle(Style.STROKE);

        mPaint.setStrokeWidth(50);

//        mPaint.setColor(mPaintColor);

        mPaint.setStrokeCap(Paint.Cap.ROUND);  //圆头

        mPaint.setDither(true);//消除拉动，使画面圓滑

        mPaint.setStrokeJoin(Paint.Join.ROUND); //结合方式，平滑

        mPaint.setAlpha(0); ////

        mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));

    }

}

////////在Activity中显示以上视图

setContentView(new PaintView(this));