然后编写代码来处理表单的MouseWheel事件.向下滚动(朝向您)会导致MouseEventArgs的Delta属性为负值.向上滚动显然是相反的. Delta属性的值始终为120.

微软的这个价值的原因如下：

Currently,a value of 120 is the standard for one detent. If higher resolution mice are introduced,the definition of WHEEL_DELTA might become smaller. Most applications should check for a positive or negative value rather than an aggregate total.

在您的上下文中,您只需检查Delta的符号并执行操作.

以下是实现基本“缩放”功能的示例代码：

Public Class Form1
    Enum ZoomDirection
        None
        Up
        Down
    End Enum

    Dim CtrlIsDown As Boolean
    Dim ZoomValue As Integer

    Sub New()

        ' This call is required by the designer.
        InitializeComponent()

        ' Add any initialization after the InitializeComponent() call.
        ZoomValue = 100
    End Sub

    Private Sub Form1_KeyDown_KeyUp(ByVal sender As Object,_
                                    ByVal e As KeyEventArgs) _
                Handles Me.KeyDown,Me.KeyUp

        CtrlIsDown = e.Control
    End Sub

    Private Sub Form1_MouseWheel(ByVal sender As Object,ByVal e As MouseEventArgs) _
                Handles Me.MouseWheel

        'check if control is being held down
        If CtrlIsDown Then
            'evaluate the delta's sign and call the appropriate zoom command
            Select Case Math.Sign(e.Delta)
                Case Is < 0
                    Zoom(ZoomDirection.Down)
                Case Is > 0
                    Zoom(ZoomDirection.Up)
                Case Else
                    Zoom(ZoomDirection.None)
            End Select
        End If
    End Sub

    Private Sub Zoom(ByVal direction As ZoomDirection)
        'change the zoom value based on the direction passed

        Select Case direction
            Case ZoomDirection.Up
                ZoomValue += 1
            Case ZoomDirection.Down
                ZoomValue -= 1
            Case Else
                'do nothing
        End Select

        Me.Text = ZoomValue.ToString()
    End Sub
End Class

有关您的问题的更多信息,请阅读以下内容：

> MSDN: Control.KeyDown Event
> MSDN: Control.KeyUp Event
> MSDN: Control.MouseWheel Event
> MSDN: MouseEventArgs Class