ASP.NET Custom Server Controls: Cute Image Hover Button - Other features of the control
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Another modification to the same control is the following code fragment. Look it over carefully.
Protected Overrides Sub Render(ByVal writer As System.Web.UI.HtmlTextWriter)
If Not Page Is Nothing Then
Page.VerifyRenderingInServerForm(Me)
End If
MyBase.Render(writer)
End Sub
The above implementation of the “Render” method ensures that the placement of your control should be within the “<FORM>” tag itself. It would automatically raise an error if not placed within the “<FORM>” tag. You should also observe the second statement, “MyBase.Render(writer)”. It asks to proceed with rendering as usual, without considering any other issue.
The next question would be, how did I implement “OnClick” event within my control? The following statements at various locations made it possible:
Public Event Click As EventHandler
Public Sub RaisePostBackEvent(ByVal eventArgument As String)Implements System.Web.UI.IPostBackEventHandler.RaisePostBackEvent
OnClick(EventArgs.Empty)
End Sub
Protected Overridable Sub OnClick(ByVal e As EventArgs)
RaiseEvent Click(Me, e)
End Sub
It is the concept of both eventing and delegating together. The above statements made it possible to implement ‘postback’ing together with delegating. I suggest you to go through OOPS in .NET, if you are not familiar with Events and Delegates.
I implemented two more properties for “ImageOver” and “ImageOut” scenarios. The following shows a code fragment of one of them (the other is also quite similar):
<EditorAttribute(GetType(System.Web.UI.Design.UrlEditor), GetType(System.Drawing.Design.UITypeEditor))> _
Property [ImageOverURL] () As String
Get
Return viewstate("ImageOverURL") & ""
End Get
Set (ByVal Value As String)
viewstate("ImageOverURL") = Value
End Set
End Property
You should be able to understand everything except the “<EditorAttribute..>”. That specification is used to provide an open dialog box to select files (of images) from within the properties window during the web page design. If you omit that, you need to provide the path of the file manually (without selection).
Coming to the JavaScripts issue, I included two methods, “getJS4MouseOver” and “getJS4MouseOut” to emit JavaScript for every instance of the control. The following would give you an idea of “getJS4MouseOver” (the other is also quite similar):
Private Function getJS4MouseOver(ByVal FunctionName As String) As String
Dim js As String
js = "<script language=javascript>"
js &= "function " & FunctionName & "() "
js &= "{"
js &= " event.srcElement.style.backgroundImage='url(" & ImageOverURL & ")'; "
js &= "}"
js &= "</script>"
Return js
End Function
I just kept on concatenating the JavaScript into a single variable, and finally returned that JavaScript back to the caller. I would suggest you use “StringBuilder” rather than simply concatenating it.
Remarks
This control has been developed just to initiate and show the power of custom control to control everything right from the beginning to the end, including client-side JavaScript emission. I didn’t quite implement all of the features of original ASP.NET Button control (as that would take a series of articles). You just need to learn a few more interfaces and methods to implement all of the original features along with your own features.
I leave it to the developers to further enhance the same control. The areas in which you can improve the control would include eventing, better JavaScript for validation, data-binding, and so on. Good luck.
Any comments, suggestions, bugs, errors, feedback etc. are highly appreciated at jag_chat@yahoo.com.
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