Handling Scroll Events of a Panel Control and Other Scrollable Controls
The panel control supports scrolling of its content if the AutoScroll
property is set to True
. Nevertheless, an event for handling the scroll events is missing. This event can be added to the panel easily by deriving from the System.Windows.Forms.Panel
class (or any other scrollable control) and listening for scroll messages in the WndProc
method. The code below can be used as a replacement for the .NET Framework’s panel control:
Imports System
Imports System.Windows.Forms
''' <summary>
''' Extends the panel control by a <c>Scroll</c> event.
''' </summary>
Public Class ScrollPanel
Inherits Panel
''' <summary>
''' Occurs when the panel is scrolled.
''' </summary>
''' <param name="sender">The source of the event.</param>
''' <param name="e">
''' A <c>ScrollEventArgs</c> that contains the event data.
''' </param>
Public Event Scroll(ByVal sender As Object, ByVal e As ScrollEventArgs)
Private Const WM_VSCROLL As Int32 = &H115
Private Const WM_HSCROLL As Int32 = &H114
''' <summary>
''' Raises the <c>Scroll</c> event.
''' </summary>
''' <param name="e">
''' A <c>ScrollEventArgs</c> that contains the event data.
''' </param>
Protected Sub OnScroll(ByVal e As ScrollEventArgs)
RaiseEvent Scroll(Me, e)
End Sub
Protected Overrides Sub WndProc(ByRef m As Message)
If m.Msg = WM_HSCROLL Then
OnScroll(New ScrollEventArgs(ScrollDirection.Horizontal))
ElseIf m.Msg = WM_VSCROLL Then
OnScroll(New ScrollEventArgs(ScrollDirection.Vertical))
End If
MyBase.WndProc(m)
End Sub
End Class
''' <summary>
''' Provides data for the <c>Scroll</c> event.
''' </summary>
Public Class ScrollEventArgs
Private m_Direction As ScrollDirection
''' <summary>
''' Creates a new instance of <c>ScrollEventArgs</c>.
''' </summary>
''' <param name="Direction">
''' The initial value of the <c>Direction</c> property.
''' </param>
Public Sub New(ByVal Direction As ScrollDirection)
Me.Direction = Direction
End Sub
''' <summary>
''' Gets or sets the direction the panel has been scrolled to.
''' </summary>
''' <value>The direction the panel has been scrolled to.</value>
Public Property Direction() As ScrollDirection
Get
Return m_Direction
End Get
Set(ByVal Value As ScrollDirection)
m_Direction = Value
End Set
End Property
End Class
''' <summary>
''' Provides possible scrolling directions.
''' </summary>
Public Enum ScrollDirection
''' <summary>
''' Horizontal scrolling.
''' </summary>
Horizontal
''' <summary>
''' Vertical scrolling.
''' </summary>
Vertical
End Enum
ScrollPanel
provides a Scroll
event that is raised when the panel is scrolled. The event handler receives a ScrollEventArgs
object that gives information about the scrolling direction.