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ViewState management for dynamically loaded UserControls

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30 Apr 2007CPOL2 min read 70.5K   1.1K   16   26
ViewState management for dynamically loaded UserControls.

Introduction

In many of our business ASPX applications, there is a need for special UserControls that perform specific functionalities so that they can be easily re-used in the entire application. There are two ways we can use a UserControl: either we drag it onto the form, or we load it dynamically through the use of LoadControl("MyUserControl.ascx"). When we use the second method, we (all?) encounter one major problem: ViewState persistence! Upon postback, when we re-load the control in our CS code, .NET Framework forgets everything about its previous state. This tiny essay addresses this issue.

Solution!

Straightforward: assign the dynamically loaded control the same ID it had just before the data postback! In fact, .NET Framework retains the state of every user control (even of those dynamically loaded) and associate them with their programmatic IDs; after a postback, it tries to find the same controls with the same IDs in order to load their previous state. The whole thing can better be explained through an example :-)

Example

We'll create a simple UserControl which has a TexBox, we'll also have an ASPX form on which we use this control but in three ways. For this purpose, we'll create three instances:

  • An instance which is already dragged onto the form
  • An instance dynamically created through LoadControl()
  • An instance dynamically created through LoadControl() with its ID preserved

I have created a simple UserControlViewStateManager that will help us automatically save/load the dynamically loaded controls and their IDs. The main idea behind this gadget is to save the ID of the UserControls right after loading them into their parent container and re-creating them after the postback: the best place for re-creating the controls is the Page_Init event.

When creating a new user control: just give a unique ID and at the same time, add it to an instance of the UserControlViewStateManager. Shown below is a snippet:

C#
Control userControl = LoadControl("MyUserControl.ascx");
userControl.ID = (placeHolder2.Controls.Count - 1).ToString();
placeHolder2.Controls.Add(userControl);
ucViewStateManager.AddControl(userControl);

In the Page_Init event, call ReCreateControlsID() of the helper class, passing it the container object as a parameter:

C#
ucViewStateManager = new UserControlViewStateManager("SomeUniqueSessionID");
ucViewStateManager.ReCreateControlsID(placeHolder2);

Hope this helps :-) In the demo application, you can find the entire source code.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


Written By
Software Developer (Senior)
Hungary Hungary
Professional Software Developer, currently working for HVB bank.
Programming experience includes: C#, ASP.NET, Delphi, PHP, VB.
Technologies: MS SQL Server 2005, Apache, IIS.

Certifications: MCAD, MCSD, MCTS (MS SQL Server 2005), MCITP

Comments and Discussions

 
QuestionI am not able to add user control multiple time Pin
Member 1363471321-Jan-18 0:14
Member 1363471321-Jan-18 0:14 
GeneralMore about Dinamically added controls Pin
rafael.aca14-Apr-09 12:06
rafael.aca14-Apr-09 12:06 
GeneralDynamice Usercontrol .ascx Pin
Kurmala13-Jul-08 19:50
Kurmala13-Jul-08 19:50 
Hi,
I am working on Dynamic User controls that is .ascx on a single aspx page.
I have aspx where i have link buttons on that when i click on a link it has to load ascx control on that page. It is working properly but the main problem is when i am using back button and performing action on that usercontrol it is giving error . will plz help me for that .
GeneralUser Controls Piling UP on Page [modified] Pin
stanz927-Feb-08 7:04
stanz927-Feb-08 7:04 
GeneralIs this a sure tested method of loading usercontrols dynamically Pin
xsoftdev19-Feb-08 13:12
xsoftdev19-Feb-08 13:12 
GeneralPass values to other user controls Pin
xsoftdev18-Oct-07 15:55
xsoftdev18-Oct-07 15:55 
GeneralRe: Pass values to other user controls Pin
Wesam Elsawirki20-Oct-07 3:56
Wesam Elsawirki20-Oct-07 3:56 
GeneralRe: Pass values to other user controls Pin
xsoftdev26-Nov-07 6:52
xsoftdev26-Nov-07 6:52 
GeneralLoad one and Unload the others Pin
xsoftdev4-Oct-07 9:00
xsoftdev4-Oct-07 9:00 
GeneralRe: Load one and Unload the others Pin
Wesam Elsawirki8-Oct-07 20:04
Wesam Elsawirki8-Oct-07 20:04 
GeneralUserControl Pin
Brother Louis20-Aug-07 0:54
Brother Louis20-Aug-07 0:54 
GeneralRe: UserControl Pin
Wesam Elsawirki8-Oct-07 19:59
Wesam Elsawirki8-Oct-07 19:59 
Questionquestion from manish.2004 Pin
Sean Ewington1-Jun-07 9:04
staffSean Ewington1-Jun-07 9:04 
AnswerRe: question from manish.2004 Pin
Wesam Elsawirki4-Oct-07 20:23
Wesam Elsawirki4-Oct-07 20:23 
GeneralRe: question from manish.2004 Pin
xsoftdev22-Nov-07 0:50
xsoftdev22-Nov-07 0:50 
QuestionIssues at Page PostBack Pin
Mohamad K.27-Apr-07 10:40
Mohamad K.27-Apr-07 10:40 
QuestionThread-Safe ??? Pin
Marco M.18-Apr-07 9:06
Marco M.18-Apr-07 9:06 
AnswerRe: Thread-Safe ??? Pin
Johnno7423-Apr-07 16:57
Johnno7423-Apr-07 16:57 
GeneralRe: Thread-Safe ??? Pin
Wesam Elsawirki30-Apr-07 0:08
Wesam Elsawirki30-Apr-07 0:08 
GeneralRe: Thread-Safe ??? Pin
Johnno7430-Apr-07 12:50
Johnno7430-Apr-07 12:50 
GeneralControl issue Pin
Volleyknaller17-Apr-07 22:39
Volleyknaller17-Apr-07 22:39 
GeneralRe: Control issue Pin
Wesam Elsawirki18-Apr-07 0:35
Wesam Elsawirki18-Apr-07 0:35 
GeneralRe: Control issue Pin
Volleyknaller18-Apr-07 1:18
Volleyknaller18-Apr-07 1:18 
QuestionPostback issue Pin
ryanoc33317-Apr-07 11:01
ryanoc33317-Apr-07 11:01 
AnswerRe: Postback issue Pin
Wesam Elsawirki17-Apr-07 19:59
Wesam Elsawirki17-Apr-07 19:59 

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