Auto Resize Dropdown Box

Auto Resize Dropdown

Sometimes, using a built-in dropdown control does not meet your requirement. Suppose a dropdown box contains text that is longer in length than your box; therefore, the width of the dropdown will increase as the text length increases. But, an increase in the dropdown's size affects your form design. You don't have enough space on your page to fit this lengthy dropdown box. In that case, you can use this Auto Resize Dropdown box.

Create a blank solution; in the solution, add a class library; and in the class file, add the following code. This code shows that, at the time of rendering the control, with the help of a style you can maintain the initial width of your dropdown box.

Note: You must inherit WebControls.DropDownList.
Inherits WebControls.DropDownList
   Protected Overrides Sub Render(ByVal writer As _
      System.Web.UI.HtmlTextWriter)
      writer.Write("<div style='width:" & Me.Width.ToString & "'>")
      MyBase.Render(writer)
      writer.WriteEndTag("div")
End Sub

At the time of initialization, it will call JavaScript functions. These JavaScript functions will attach with onactivate and ondeactivate events.

Private Sub AutoSizeDropDown_Init(ByVal sender As Object, _
   ByVal e As System.EventArgs) Handles Me.Init
   Dim ControlsJS As String
   ControlsJS = "<script type=""text/javascript"" src=""" & 
   HttpRuntime.AppDomainAppVirtualPath & "/js/CustomControls.js""> _
   </script>"
   Me.Attributes.Add("originalWidth", "")
   Me.Attributes.Add("onactivate", "RearrangeDdnWidth(this)")
   Me.Attributes.Add("ondeactivate", "ResetDdnWidth(this)")
   Page.ClientScript.RegisterClientScriptBlock(Me.GetType(), _
      "ControlsJS", ControlsJS)
End Sub

After building the solution, add a new web site in your solution. In the default.aspx page, register your DLL with the page.

<%@ Register Assembly="AutoDropDown"
    Namespace="AutoDropDown" TagPrefix="cc1" %>

After that, you can add the dropdown:

<cc1:AutoSizeDropDown runat="server"
                      ID="AutoSizeDropDown1"
                      Width="50px"></cc1:AutoSizeDropDown>

The complete source code is available with this article.



About the Author

Ashish Singh

I am working as I.T. Analyst at Tata Consultancy Services Ltd. I have 4+ years of experience in Microsoft Technologies. I have worked primarily as a Dot Net Developer with C# and VB.Net as code behind.

Downloads

Comments

  • There are no comments yet. Be the first to comment!

Leave a Comment
  • Your email address will not be published. All fields are required.

Top White Papers and Webcasts

  • Live Event Date: October 29, 2014 @ 11:00 a.m. ET / 8:00 a.m. PT Are you interested in building a cognitive application using the power of IBM Watson? Need a platform that provides speed and ease for rapidly deploying this application? Join Chris Madison, Watson Solution Architect, as he walks through the process of building a Watson powered application on IBM Bluemix. Chris will talk about the new Watson Services just released on IBM bluemix, but more importantly he will do a step by step cognitive …

  • Mobile devices, social business apps, and business analytics are converging with the Cloud to create the most substantial changes in technology since the Internet revolution. Businesses have to change the way they think and operate, and with rising budgets for technology, they need someone to provide the services that will keep them competitive in this environment. Learn more about the important technology trends you need to stay on top of to ensure your business doesn't get left behind.

Most Popular Programming Stories

More for Developers

Latest Developer Headlines

RSS Feeds