编程必学：控件的拖动和缩放技术全解
一、光标的指示
当光标移动到要拖动或缩放的控件上时，应显示相应的动作箭头。定义一个枚举的变量来标识对应的状态。
Enum EnumMousePointPosition
MouseSizeNone = 0 '无
MouseSizeRight = 1 '拉伸右边框
MouseSizeLeft = 2 '拉伸左边框
MouseSizeBottom = 3 '拉伸下边框
MouseSizeTop = 4 '拉伸上边框
MouseSizeTopLeft = 5 '拉伸左上角
MouseSizeTopRight = 6 '拉伸右上角
MouseSizeBottomLeft = 7 '拉伸左下角
MouseSizeBottomRight = 8 '拉伸右下角
MouseDrag = 9 '鼠标拖动
End Enum
Dim m_MousePointPosition As EnumMousePointPosition
在MouseMove事件中读取进入控件的光标位置，用下面函数判断光标的状态。
m_MousePointPosition = MousePointPosition(sender.Size, e)
按对应的状态显示光标形状
Select Case m_MousePointPosition
Case EnumMousePointPosition.MouseSizeNone
Me.Cursor = Cursors.Arrow
'箭头
Case EnumMousePointPosition.MouseDrag
Me.Cursor = Cursors.SizeAll
'四方向
Case EnumMousePointPosition.MouseSizeBottom
Me.Cursor = Cursors.SizeNS
'南北
Case EnumMousePointPosition.MouseSizeTop
Me.Cursor = Cursors.SizeNS
'南北
Case EnumMousePointPosition.MouseSizeLeft
Me.Cursor = Cursors.SizeWE
'东西
Case EnumMousePointPosition.MouseSizeRight
Me.Cursor = Cursors.SizeWE
'东西
Case EnumMousePointPosition.MouseSizeBottomLeft
Me.Cursor = Cursors.SizeNESW
'东北到南西
Case EnumMousePointPosition.MouseSizeBottomRight
Me.Cursor = Cursors.SizeNWSE
'东南到西北
Case EnumMousePointPosition.MouseSizeTopLeft
Me.Cursor = Cursors.SizeNWSE
'东南到西北
Case EnumMousePointPosition.MouseSizeTopRight
Me.Cursor = Cursors.SizeNESW
'东北到南西
End Select
如果光标离开控件，MouseMove事件将不响应，因此用需用MouseLeave事件来接力完成光标状态的标识和显示。
Private Sub MyMouseLeave(ByVal sender As Object, ByVal e As System.EventArgs)
m_MousePointPosition = EnumMousePointPosition.MouseSizeNone
Me.Cursor = Cursors.Arrow
End Sub
二、拖动
拖动的原理是移动控件的Location到当前光标的位置，并保持控件的高度和宽度不变。如果记录起始光标点为p，当前光标点为e，那么x方向的移动距离是e.X - p.X，x方向的移动距离是e.Y - p.Y。
在鼠标按下时，即是拖动的开始，在MouseDown事件中，记录光标开始拖动点
p = New Point(e.X, e.Y)
在MouseMove事件，检测是否持续按着鼠标左键，如果是则更新控件的起点位置
If e.Button = MouseButtons.Left Then
sender.Location = New Point(sender.Left + e.X - p.X, sender.Top + e.Y - p.Y)
End If
三、缩放
缩放的原理和拖动类似，如果缩放底边，就是根据光标的移动改变控件的高度，而不改变控件的起点位置。
同样，如果缩放底边，在鼠标按下时，即是缩放的开始，在MouseDown事件中，记录光标开始拖动点
p = New Point(e.X, e.Y)
在MouseMove事件，检测是否持续按着鼠标左键，如果是则更新控件的高度
If e.Button = MouseButtons.Left Then
sender.Size = New Size(sender.Width, sender.Height + e.Y - p1.Y)
p1 = New Point(e.X, e.Y)
'记录光标拖动的当前点
End If
这里和拖动有些区别，就是高度的变化会导致光标位置数值的变化，因此需重新用p1定位光标起始点的位置。所有涉及控件底边和右边的缩放都要这样处理，而左边和顶边则不用。
其它所有各方向的拖动都可以类推。
四、委派
所有的操作，一共总结为三个函数，MyMouseDown，MyMouseMove，MyMouseLeave。
动态创建控件后，需委派相应的事件到这三个函数。如果创建一个按钮，
Dim Button As New Button
Controls.Add(Button)
AddHandler Button.MouseDown, AddressOf MyMouseDown
AddHandler Button.MouseMove, AddressOf MyMouseMove
AddHandler Button.MouseLeave, AddressOf MyMouseLeave
五、源码
建立一个窗体，放置一个按钮，点击该按钮创建动态建立一个可以拖动和缩放的按钮。全部源码如下：
Public Class Form1
Inherits System.Windows.Forms.Form
Enum EnumMousePointPosition
MouseSizeNone = 0 '无
MouseSizeRight = 1 '拉伸右边框
MouseSizeLeft = 2 '拉伸左边框
MouseSizeBottom = 3 '拉伸下边框
MouseSizeTop = 4 '拉伸上边框
MouseSizeTopLeft = 5 '拉伸左上角
MouseSizeTopRight = 6 '拉伸右上角
MouseSizeBottomLeft = 7 '拉伸左下角
MouseSizeBottomRight = 8 '拉伸右下角
MouseDrag = 9 '鼠标拖动
End Enum
Dim m_MousePointPosition As EnumMousePointPosition
Dim p, p1 As Point
Private Sub MyMouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs)
p = New Point(e.X, e.Y)
'记录光标开始拖动点
p1 = New Point(e.X, e.Y)
End Sub
Private Sub MyMouseLeave(ByVal sender As Object, ByVal e As System.EventArgs)
m_MousePointPosition = EnumMousePointPosition.MouseSizeNone
Me.Cursor = Cursors.Arrow
End Sub
Private Sub MyMouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs)
If e.Button = MouseButtons.Left Then
Select Case m_MousePointPosition
Case EnumMousePointPosition.MouseDrag
sender.Location = New Point(sender.Left + e.X - p.X, sender.Top + e.Y - p.Y)
Case EnumMousePointPosition.MouseSizeBottom
sender.Size = New Size(sender.Width, sender.Height + e.Y - p1.Y)
p1 = New Point(e.X, e.Y)
'记录光标拖动的当前点
Case EnumMousePointPosition.MouseSizeBottomRight
sender.Size = New Size(sender.Width + e.X - p1.X, sender.Height + e.Y - p1.Y)
p1 = New Point(e.X, e.Y)
Case EnumMousePointPosition.MouseSizeRight
sender.Size = New Size(sender.Width + e.X - p1.X, sender.Height)
p1 = New Point(e.X, e.Y)
Case EnumMousePointPosition.MouseSizeTop
sender.Location = New Point(sender.Left, sender.Top + (e.Y - p.Y))
sender.Size = New Size(sender.Width, sender.Height - (e.Y - p.Y))
Case EnumMousePointPosition.MouseSizeLeft
sender.Location = New Point(sender.Left + e.X - p.X, sender.Top)
sender.Size = New Size(sender.Width - (e.X - p.X), sender.Height)
Case EnumMousePointPosition.MouseSizeBottomLeft
sender.Location = New Point(sender.Left + e.X - p.X, sender.Top)
sender.Size = New Size(sender.Width - (e.X - p.X), sender.Height + e.Y - p1.Y)
p1 = New Point(e.X, e.Y)
Case EnumMousePointPosition.MouseSizeTopRight
sender.Location = New Point(sender.Left, sender.Top + (e.Y - p.Y))
sender.Size = New Size(sender.Width + (e.X - p1.X), sender.Height - (e.Y - p.Y))
p1 = New Point(e.X, e.Y)
Case EnumMousePointPosition.MouseSizeTopLeft
sender.Location = New Point(sender.Left + e.X - p.X, sender.Top + (e.Y - p.Y))
sender.Size = New Size(sender.Width - (e.X - p.X), sender.Height - (e.Y - p.Y))
End Select
Else
m_MousePointPosition = MousePointPosition(sender.Size, e)
'判断光标的位置状态
Select Case m_MousePointPosition
'改变光标