如何更改起始点drawrect customview android

public class CustomView extends View {
    private int startPointX;
    private int startPointY;

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

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

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

    private void init() {
        // 初始化起始点的位置
        startPointX = 100;
        startPointY = 100;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        // 绘制矩形
        Paint paint = new Paint();
        paint.setColor(Color.RED);
        canvas.drawRect(startPointX, startPointY, startPointX + 200, startPointY + 200, paint);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        // 测量视图的大小
        int width = MeasureSpec.getSize(widthMeasureSpec);
        int height = MeasureSpec.getSize(heightMeasureSpec);
        setMeasuredDimension(width, height);
    }
}