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Accessing Data From Dynamically Created Controls Using ASP.NET 2.0 Callback

, 19 Feb 2006 72.6K 674 27
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Storing and retreiving data input from dynamically created controls without the need to recreate the controls after postback.

Introduction

Adding controls to an ASP.NET WebForm at runtime is a simple task:

private void Page_Load(object sender, System.EventArgs e)
{
    Button newButton = new Button();
    newButton.Text = "New Button"; 
    newButton.ID = "newButton"; 
    newButton.Click += new System.EventHandler(this.newButton_Click); 

    WebUserControl1 newUserControl = 
           (WebUserControl1)LoadControl("WebUserControl1.ascx"); 
    newUserControl.ID = "newUserControl";
    this.PlaceHolder.Add(newUserControl); 
    this.PlaceHolder.Add(newButton);
}

Problem

Now, let's raise a bit little. What if we want to add a new control as a result of some user action (button click, for example)? We are moving the same code from Page_Load to Button_Click event and… here troubles begin. Our controls will show as expected, but only the first time. Any postback will reset the page to its original state. Dynamically created controls will be unable to fire any event. What is happening here? The answer is simple. Page class is stateless. It is destroyed after rendering. Page recreates child controls collection, based on tags in aspx file, then postback data can be handled and event handlers attached (in OnInit event). Controls we just created dynamically do not exist in aspx file; Page has no knowledge about them.

Solution

The solution is also simple. We have to recreate controls on load stage of page lifecycle. After it's done, each control can handle its postback data, retrieve saved viewstate, raise events etc.

Now, the code skeleton will look like this:

private void Page_Load(object sender, System.EventArgs e)
{
    RecreatePersistedControls();
}
private void Button_Click(object sender, System.EventArgs e)
{
    CreateControl("newControl");
    PersistControl("newControl");
}
private void RecreatePersistedControls()
{
    // Call CreateControl for each persisted control
}
private void CreateControl(string id)
{
    // Create controll with specified id, 
    // add it to controls collection, attach event handlers
}
private void PersistControl(string id)
{
    // Persist specified id (in session for example)
}

Download source files to see the fully functional sample.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

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About the Author

vineyard
Web Developer
United States United States
Possess over 17 years of experience and expertise in the IT industry. Possess in-depth knowledge and experience in the areas of database development, modeling, implementation, wireless integration, and migration, extensive web development skills, and several years of experience providing consulting and training services. Extensive work experience on several integration project for Dell Corporation, Fujitsu, Scholle, Sperry Marine, Vought Aircraft to name a few. Complete understanding of the importance of meeting timelines and budgetary restraints on a per project basis.

As a key member of Brady Systems Integration, created solutions that automated data collection from manufacturing and warehouse thru wireless devices like Symbol, Intermec, and HHP and integrated that data and transactions into the clients back-end business systems. Possess experience integrating into Baan, SAP, JD Edwards, and Great Plaines ERP Systems.

Technical skills include VS.net, Visual Basic, VB.net, C#, ASP.net, J# Palm/OS, Java, Websphere, Lotus Notes/Domino, Ajax, Cold Fusion, XML, MS SQL Server, and Oracle.

Microsoft Universal Development Program Partner

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Comments and Discussions

 
GeneralDoesn't work for dropdowns Pin
GeorgeMar21-Feb-06 3:49
memberGeorgeMar21-Feb-06 3:49 
GeneralRe: Doesn't work for dropdowns Pin
vineyard21-Feb-06 4:19
membervineyard21-Feb-06 4:19 
GeneralRe: Doesn't work for dropdowns Pin
GeorgeMar21-Feb-06 4:26
memberGeorgeMar21-Feb-06 4:26 
GeneralRe: Doesn't work for dropdowns Pin
vineyard21-Feb-06 4:45
membervineyard21-Feb-06 4:45 
GeneralRe: Doesn't work for dropdowns Pin
simone massaro21-Feb-06 9:46
membersimone massaro21-Feb-06 9:46 
GeneralRe: Doesn't work for dropdowns Pin
GeorgeMar22-Feb-06 4:13
memberGeorgeMar22-Feb-06 4:13 
GeneralRe: Doesn't work for dropdowns Pin
GeorgeMar22-Feb-06 4:14
memberGeorgeMar22-Feb-06 4:14 
GeneralRe: Doesn't work for dropdowns Pin
vineyard22-Feb-06 4:28
membervineyard22-Feb-06 4:28 
GeneralRe: Doesn't work for dropdowns Pin
thisguyinoc14-Jun-06 8:15
memberthisguyinoc14-Jun-06 8:15 
GeneralRe: Doesn't work for dropdowns Pin
Ankit M1-Mar-07 7:43
memberAnkit M1-Mar-07 7:43 

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