CODEWITHSUNDEEP
c#asp.net.net
avivas
avivas

Reputation: 173

Dynamically add and remove a User Control from a Page

I have a Web User Control that I need to add to a page simply in order to add it to an HtmlForm so I can send an email with this User Control, however, I do not need this Control to appear on the page, I just need it to fill with data so I can send this email, and then be removed so it does not appear on the page.

Currently I have tried:

myControl c = new myControl();
c.InitializeAsUserControl(Page);
c.fillInfo(data);

//add to email form and send email

yet this adds the control to the current page on post back once the email has been sent and a confirmation message

I have also tried

myControl c = (myControl)Page.LoadControl("~/filename.ascx");
//send email
Page.Controls.Remove(c);

yet this also renders the control on the page and does not remove it. I have tried to add it to a panel and set Visible to false, but unfortunately this does not work either. If I simply create a new myControl() without rendering on page or calling LoadControl I get exceptions thrown when fillInfo is called when it tries to modify asp:labels in the User Control saying that the objects are null or not instantiated.

Upvotes: 1

Views: 2320

Answers (2)

Jon Adams
Jon Adams

Reputation: 25137

I suggest reading the entire TRULY UNDERSTANDING DYNAMIC CONTROLS series. To successfully use dynamic controls with postbacks, viewstate, bindings, and the other WebForms features, you really have to know the page and control lifecycles and their interactions inside out.

When you load and set ViewState depends on the cycle. ViewState is loaded between Page_Init and Page_Load, so the control has to be in Page_Init. However, any processing based on auto-loaded ViewState, needs to go in Page_Load. Where/when ViewState is enabled depending on the control hierarchy can also affect this. I suggest you read that guide above in depth if you really want it to work. Or, you'll have to post your entire control code and its use in a page for us to tell you which parts you are missing or have in the wrong part of the page lifecycle.

I've made dynamic controls work, but 99% of the time, unless the control is extremely trivial, it's easier to find a different solution than it is to make sure all the interactions work correctly with dynamic control creation.

Upvotes: 1

Crab Bucket
Crab Bucket

Reputation: 6277

Which part of the page cycle are you loading and unloading the controls? To work properly it needs to be done in Page_Init. It's a common mistake to do it in Page_Load. If it is added anywhere else other than Page_Init it won't be added to the ViewState correctly and problems will ensue.

Rather than unload - I would add it to a Panel and set Visibility to false. Could be the reason that isn't working for you at the moment is that the control is being added at the wrong part of the page cycle and isn't being added to ViewState correctly.

Could that be your problem?

Upvotes: 1

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