Point结构体中Subtract和Add方法在拖曳控件时的应用

  结构体 Point 中方法Subtract()和Add()可用于在同一个坐标系中2点之间相对位置的计算:

public static Point Subtract(
 Point pt,
 Size sz
)

public static Point Add(
 Point pt,
 Size sz
)

而 Size 可以通过 Point 转换, 如下Size的一个构造函数:
public Size(
 Point pt
)

下面以处于同一容器下(Form1)的2个组件 label1, label2 , 当拖曳第一个组件label1时, label2也同时跟着移动.

1. 定义全局字段:

private Point label1StartPos, offsetPoint;
private bool canMove = false;

2. 相关事件方法:

        private void label1_MouseDown(object sender, MouseEventArgs e)
        {
            canMove = true;
            label1StartPos = e.Location;
            offsetPoint = Point.Subtract(label2.Location, new Size(label1.Location));
        }

        private void label1_MouseUp(object sender, MouseEventArgs e)
        {
            canMove = false;
        }

        private void label1_MouseMove(object sender, MouseEventArgs e)
        {
            if (canMove)
            {
                label1.Location = this.PointToClient(Point.Subtract(label1.PointToScreen(e.Location), new Size(label1StartPos)));
                label2.Location = Point.Add(label1.Location, new Size(offsetPoint));
            }
        }

 即可.