Scrollable Picturebox Custom Control in VB.NET


This article discusses the construction of a custom control used to add a scrollable Picturebox control to a project. There are different ways to scroll an image; it can be done using GDI+ for example, but the approach used in this demo is based upon what I feel is the easiest approach; that being to just scroll a full sized image contained within a panel control set to auto size. By building the control as a custom control, you can reuse in any application where you might need to provide such capability.


Figure 1: Custom Control Loaded into a Test Application

Since the control is based upon the panel control, you will pick up all of the properties contained in the panel control which will make this simple control immediately more useful (for example, you will be able to dock the control into a form).

Getting Started:

In order to get started, unzip the included project and open the solution in the Visual Studio 2008 environment. There are two projects contained in the solution. TestControl is the first project and it is Windows form application used to test the custom control. The second project (XPicboxVB) is class library containing a single custom control called XtendPicBox.vb.
In the solution explorer, you should note these items:


Figure 2: Solution Explorer

The Custom Control (XtendPicBox.vb)

The extended picture box custom control contains everything necessary to display an image in a scrollable container. The control itself is an extension of the panel control. Within the extended control, a picture box control is configured and added to the panel's control collection. When the control is initialized, the picture box is set to the upper left corner of the control and its size mode is set to normal. Properties within the control are used to both limit the consumer's access to the auto scroll property of the panel control (it has to be set to true in order for the image to scroll) and to allow the consumer to set the image file displayed in the inner picture box at both design and runtime.

The custom control class begins with the following library imports:

Imports System.ComponentModel
Imports System.Drawing
Imports System.Windows.Forms

Following the imports, the class is defined. A constructor is added as are a collection of local member variables. The local member variables include the declaration of the inner Picturebox control, the path to the Picturebox image, and a Boolean value used to set auto scroll to true (for the extended panel control). The constructor is used to configure the Picturebox and to add the Picturebox control to the extended panel control.

''' <summary>

''' Extend the standard panel control

''' to serve as a scrollable picture

''' box control

''' </summary>

''' <remarks></remarks>

Public Class XtendPicBox

    Inherits Panel

#Region "Local Member Variables"


    ''' <summary>

    ''' Collection of member variables used to

    ''' support the display of the picturebox,

    ''' maintain the path to the image file,

    ''' and to lock the panel into remaining in

    ''' auto scroll mode

    ''' </summary>

    ''' <remarks></remarks>

    Private innerPicture As New PictureBox()

    Private mPictureFile As String = String.Empty

    Private mAutoScroll As Boolean = True

#End Region

#Region "Constructor"


    ''' <summary>

    ''' Constructor - set up the inner

    ''' picture box so that is plants itself

    ''' in the top left corner of the panel

    ''' and so that its size mode is always

    ''' set to normal.  At normal, the picture

    ''' will appear at full size.

    ''' </summary>

    Public Sub New()




        ' add the inner picture

        innerPicture.Top = 0

        innerPicture.Left = 0

        innerPicture.SizeMode = PictureBoxSizeMode.Normal 


    End Sub 

#End Region

Next up are the custom control's properties. The first property is used to set the image file to be displayed within the inner Picturebox control. Attributes are set to describe the purpose of the property when that property is used within the IDE; the attributes also specify that the property will be set using the file name editor; this will support opening a file browser window within the IDE at design time if the control consumer chooses to set the image file at design time. If the editor were not specified here, the control consumer would have to key in the path the image file.

The second property merely overrides the extended panel control's auto scroll property. By overriding the property and setting up the Browsable attribute to false, the control consumer will be denied the ability to set the property using the property editor at design time. Since we always want the panel's auto scroll property set to true, we block access to the property and set the value within the custom control's code.


#Region "Properties"


    ''' <summary>

    ''' Maintain the path to the current

    ''' inner picture box image file

    ''' </summary>

    ''' <value></value>

    ''' <returns></returns>

    ''' <remarks></remarks>

    <Category("Image File")> _

    <Browsable(True)> _

    <Description("Set path to image file.")> _

    <Editor(GetType(System.Windows.Forms.Design.FileNameEditor), _

      GetType(System.Drawing.Design.UITypeEditor))> _

    Public Property PictureFile() As String


            Return mPictureFile

        End Get


        Set(ByVal value As String)

            mPictureFile = value


            If String.IsNullOrEmpty(mPictureFile) = False Then

                ' set the image to the image file

                innerPicture.Image = Image.FromFile(mPictureFile) 

                ' resize the image to match the image file

                innerPicture.Size = innerPicture.Image.Size 

            End If 

        End Set 

    End Property

    ''' <summary>

    ''' Override the auto scroll property

    ''' and use the browsable attribute

    ''' to hide it from control consumer

    ''' The property will always be set

    ''' to true so that the picturebox will

    ''' always scroll

    ''' </summary>

    <Browsable(False)> _

    Public Overrides Property AutoScroll() As Boolean


            Return mAutoScroll

        End Get

        Set(ByVal value As Boolean)

            mAutoScroll = value

        End Set

    End Property 

#End Region 

End Class

That is all there is to building the custom control. Once compiled, you may use the control in any project where this sort of functionality is needed.

The Test Form (Form1.vb).

Looking at the test project, you will find a single form containing a menu with File->Open and File->Exit functions defined and you will find a single instance of the custom control. The custom control is docked full within the form. There is not a lot of code here to worry about; the file open method does demonstrate the ability to set the control's image file at runtime so you might want to take a look at that. The entire body of code for the test form is as follows:


Public Class Form1

    Private Sub openToolStripMenuItem_Click(ByVal _

    sender As System.Object, ByVal e As System.EventArgs) _

    Handles openToolStripMenuItem.Click

        ' create new open file dialog

        Dim openFileDialog1 As New OpenFileDialog()

        ' configure the open file dialong

        openFileDialog1.Title = "Open Image File"

        openFileDialog1.Filter = "Bitmap Files|*.bmp" + _"|Enhanced Windows MetaFile|*.emf" + _"|Exchangeable ImageFile| *.exif" + _"|Gif Files|*.gif|Icons|*.ico|JPEG Files|*.jpg" + _"|PNG Files|*.png|TIFF Files|*.tif|Windows MetaFile|*.wmf" 

        openFileDialog1.FilterIndex = 6

        openFileDialog1.FileName = String.Empty


        ' show the dialog to the user



        ' if the user returns an empty path to an image

        ' file, return and do nothing

        If String.IsNullOrEmpty(openFileDialog1.FileName) = True Then


        End If


        ' set the extended picturebox control's

        ' image to the open file dialog's filename

        xtendPicBox1.PictureFile = openFileDialog1.FileName


    End Sub

    ''' <summary>

    ''' Standard application exit call

    ''' </summary>

    ''' <param name="sender"></param>

    ''' <param name="e"></param>

    ''' <remarks></remarks>

    Private Sub exitToolStripMenuItem_Click(ByVal _

    sender As System.Object, ByVal e As System.EventArgs) _

    Handles exitToolStripMenuItem.Click


        ' shut it down



    End Sub 

End Class


This solution provides a custom control which may be used to display image files in a scrollable container. The methods used within the control are nothing new or novel; the project does provide a simple example of how to construct a custom control, how to extend an existing control, and how to add design time support to a custom control. The same approaches to building this custom control may be applied to constructing other custom controls.