在android中绘制单点触控运动路径

public class SinglePointPathView extends ViewGroup {
    private Path mPath;
    private Paint mPaint;
    private Canvas mCanvas;
    private Bitmap mBitmap;

    public SinglePointPathView(Context context) {
        super(context);
        init();
    }

    public SinglePointPathView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public SinglePointPathView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    private void init() {
        mPath = new Path();
        mPaint = new Paint();
        mPaint.setColor(Color.BLACK);
        mPaint.setAntiAlias(true);
        mPaint.setStrokeWidth(10);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
        mCanvas = new Canvas(mBitmap);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawPath(mPath, mPaint);
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        return true;
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int action = event.getAction();
        float x = event.getX();
        float y = event.getY();

        switch (action) {
            case MotionEvent.ACTION_DOWN:
                mPath.moveTo(x, y);
                break;
            case MotionEvent.ACTION_MOVE:
                mPath.lineTo(x, y);
                break;
            case MotionEvent.ACTION_UP:
                break;
        }

        mCanvas.drawPath(mPath, mPaint);
        invalidate();
        return true;
    }
}

public class MainActivity extends AppCompatActivity {
    private SinglePointPathView mPathView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mPathView = new SinglePointPathView(this);
        mPathView.setLayoutParams(new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT));
        ((ViewGroup) findViewById(android.R.id.content)).addView(mPathView);
    }
}