画图，然后触摸可以滑动

public class DrawView extends View {
    public DrawView(Context context) {
        super(context);
    }
    public DrawView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }

    public DrawView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    private int cx = 100;
    private int cy = 100;
    /**
     * Canvas canvas画布.....paint画笔
     * @param canvas
     */
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        //中心点x坐标,y坐标,半径,画笔
        Paint paint = new Paint();
        paint.setColor(Color.RED);//设置颜色

        paint.setStrokeWidth(2);//描边的宽度2个像素
        //Paint.Style.FILL填充,,Paint.Style.STROKE描边 ,,Paint.Style.FILL_AND_STROKE填充并且描边
        paint.setStyle(Paint.Style.FILL);
        paint.setAntiAlias(true);//设置抗锯齿

        canvas.drawCircle(cx,cy,100,paint);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {

        switch (event.getAction()){
            case MotionEvent.ACTION_DOWN:
                cx = (int) event.getX();
                cy = (int) event.getY();

                break;
            case MotionEvent.ACTION_MOVE:
                cx = (int) event.getX();
                cy = (int) event.getY();
                break;
            case MotionEvent.ACTION_UP:
                cx = (int) event.getX();
                cy = (int) event.getY();
                break;
        }

        //重新绘制....自动去调用onDraw
        postInvalidate();//.........可以使用在子线程
        //invalidate();//...只能用在主线程

        return true;
    }
}

在activity中引用即可