Custom Image Button Control for ASP.NET 2.0 in VB.NET

Scott Lysle
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Introduction:

This article describes an easy approach to the construction of a custom ASP.NET 2.0 image button control that contains both a mouse-over effect and calls a JavaScript function when clicked. Whilst the article is pretty simple and the code fairly trivial, the concepts illustrated by means of this example are relatively important and are key to integrating client side functionality into an ASP.NET 2.0 project.

The two important items to pull from this article are:

That you can add attributes to a custom control, and
That you can embed and evoke JavaScript functions from a custom control.

One possible use for this control may be to drop several of them into a panel and use the panel and collection as a toolbar. Naturally the control would work just fine as a standalone control as well.

Getting Started:

In order to get started, open up the Visual Studio 2005 IDE and start a new project. From the new project dialog (Figure 1), under project types, select the "Windows" node from beneath "Visual Basic", then select the "Web Control Library" template in the right hand pane. Key in a name for the project and then click "OK".

Once the project has opened; right click on the solution and click on the "Add" menu option, and then select "New Item". When the "Add New Item" dialog appears (Figure 2), select the "Web Custom Control" template, after selecting the template, key "MOEbutton.vb" into the name field and then click "Add" to close the dialog. You may now delete the default web control that was created when the project was originally initialized from the template.

At this point, we should have an open web control library project with a single web control named "MOEbutton.vb" in that project. One last step prior to writing the code for this project will be to add in one needed reference. To add this reference, double click on the "My Project" icon in the solution explorer to open "My Project", from here, select the "References" tab, and then click the "Add" button. When the "Add Reference" dialog opens, select the .NET tab, and search down the list until you find the "System.Design" reference. Select this library and click on the "OK" button.

Figure 1: Visual Studio 2005 New Project Dialog

Figure 2: Add New Item Dialog

Navigate back to the "MOEbutton.vb" file and, at the top of the file, add in the import statement highlighted below:

Imports System

Imports System.ComponentModel

Imports System.Web

Imports System.Web.UI

Imports System.Web.UI.WebControls

Imports System.Web.UI.Design

<DefaultProperty("Text"), ToolboxData("<{0}:MOEbutton runat=server></{0}:MOEbutton>")>_

Public Class MOEbutton

Inherits WebControl

We are now ready to add the code necessary to make this control functional. First off, we need to create a few private member variables; these variables will be used to contain the paths to the image files used to display the normal and mouse-over effects on the control, to contain a string with the JavaScript to be applied to the button's on click event, and a declaration of an HTML input image control that will be used as the basis for this customization (note that the HTML Input Image button is declared with events). To accomplish these steps, create a "Declarations" region and key in the following variable declarations:

#Region "Declarations"

'create private member variables used by this control

Private mMouseOverImage As String

Private mMouseOutImage As String

Private mJavaScriptCall As String

Private WithEvents imgButton As HtmlControls.HtmlInputImage

#End Region

The next thing to do is to set up a couple of simple initialization settings; we can do that in the public sub new declaration and in the MOEbutton load event (add a Methods region and key in the following):

#Region "Methods"

Public Sub New()

'initialize new controls with a default height and width

Me.Width = 24

Me.Height = 24

End Sub

Private Sub MOEbutton_Load(ByVal sender As Object, ByVal e As

System.EventArgs) Handles Me.Load

EnsureChildControls()

End Sub

#End Region

Once the variables are declared, we will need to provide public properties to expose the control's properties to the control user; in order to accomplish these steps, create a "Properties" region and key in the following code:

#Region "Properties"

' create public properties for member variables

<Category("Button Images")>_

<Browsable(True)>_

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

<Editor(GetType(System.Web.UI.Design.UrlEditor),

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

Public Property MouseOverImage() As String

Get

Return mMouseOverImage

End Get

Set(ByVal value As String)

mMouseOverImage = value

End Set

End Property

<Category("Button Images")>_

<Browsable(True)>_

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

<Editor(GetType(System.Web.UI.Design.UrlEditor),

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

Public Property MouseOutImage() As String

Get

Return mMouseOutImage

End Get

Set(ByVal value As String)

mMouseOutImage = value

End Set

End Property

<Category("JavaScript")>_

<Browsable(True)>_

<Description("Set javascript string for onclick event.")>_

Public Property JavaScriptCall() As String

Get

Return mJavaScriptCall

End Get

Set(ByVal value As String)

mJavaScriptCall = value

End Set

End Property

#End Region

Note that, in the attributes section above each file path related property declaration, the code specifies an editor and further that the editor specified is defined as the URL Editor. Adding this attribute to the control specifies to the IDE how the property is to be edited; in this instance, when the control user sets the image file path properties for the control, the property grid will display a button with an ellipsis in it at the right hand side of the text box. If the user clicks on the button, the IDE will open the URL editor and will permit the user to use that editor to navigate to the image file and set the image file path property through that editor's dialog.

Properties set in this manner will be persisted within the control user's project. Note that the URL editor will prefix the selected path with a tilde and a slash, neither of which is useful in this context, you may wish to parse the string returned from the URL editor (in the Set region of each image file path property) to strip off the first two characters before storing the selection). This path will be passed to the "onmouseover" and "onmouseout" calls and if the tilde is present, the file will not be located.

<Editor(GetType(System.Web.UI.Design.UrlEditor), _ GetType(System.Drawing.Design.UITypeEditor))>_

At this point, the only thing left to do is to define how the control will be rendered. To complete this step, create a "Rendering" region and, within this region, override the CreateChildControls( ) sub with the following code:

#Region "Rendering"

Protected Overrides Sub CreateChildControls()

imgButton = New HtmlControls.HtmlInputImage()

imgButton.Src = MouseOutImage.ToString()

imgButton.Attributes.Add("onmouseover", "this.src='" & _

MouseOverImage.ToString() & "';")

imgButton.Attributes.Add("onmouseout", "this.src='" & _

MouseOutImage.ToString() & "';")

imgButton.Attributes.Add("onclick", JavaScriptCall.ToString())

Controls.Add(imgButton)

End Sub

#End Region

Within this code there are a few things worth looking at; first, you will note that a new instance of an HTML Input Image control is created. After this object is created, it's "src" property is set to point to the path stored for the MouseOutImage property. Next, the "onmouseover" and "onmouseout" attributes are added to the imgButton control and their image source files are set to be updated whenever the "onmouseover" or "onmouseout" events are fired. Next up, the "onclick" attribute is added to the control and the JavaScript string contained in the JavaScriptCall property is assigned to the "onclick" event. While this example is basic and uses only a string containing a simple JavaScript call, the function could also name a JavaScript function contained in an external registered JavaScript file or could contain a complex function defined within this class and subsequently registered for later use.

The control is now complete. Prior to testing the control, rebuild the project. Once that has been completed and any errors encountered are repaired, it is time to test the control. To test the control, add a new web site project to the web control library project currently open. Once the test web site has been created, set the test project as the start up project by right clicking on the web site solution in the solution explorer and selecting the "Set as Start Up Project" menu option. Next, locate the Default.aspx page in the web site solution, right click on this page and select the "Set as Start Page" menu option.

If you downloaded the project, you can configure a virtual directory pointing at the example website and examine it instead of creating one from scratch. The example project contains two subordinate projects, one containing the web class library with the single custom web control (MOEbutton) and a sample website with additional files needed to support the demonstration.

If you configure the sample project and start the default page, you will see a collection of the MOEbutton controls arranged at the top of the page in a manner similar to a toolbar. The controls each have a mouse over effect which consists of an alternate version of the normal icon, and some JavaScript calls, some to launch an alert, and one to open a new window.

Aside from the properties created in support of the MOEbutton class, as the class inherits from the WebControl class, all of the properties and methods of that class are also included at no extra charge. Therefore it requires no additional effort to permit the control user to set the background color or border characteristics, or to define tooltips without writing any additional code.

Once the site is up and running, you should observe the following displayed in your browser window.