R – ASP.NET User Controls – Problem adding multiple instances programmatically

asp.netuser-controlsweb-user-controls

I have created a user control which basically consists of 3 text boxes. I want to allow the user to click a hyperlink which will add a new instance of the user control onto a PlaceHolder. This seems to be working as I populate one of the text box controls with a random number which changes whenever I click the hyperlink. However, it is overwriting the previous control.

Heres the code on MyPage.aspx

protected void MyHyperlink_Click(object sender, EventArgs e)
{
     var uc = new MyUserControl();
     uc = (MyUserControl)LoadControl("~/path/to/my/usercontrol.ascx");
     placeHolderCtrl.Controls.Add(uc);
}

Basically what I need to know is how can I get the control adding different instances underneath eachother as it just seems to be 1 control being overwritten each time.

Thanks.

Best Answer

The problem is after the postback, your previously added controls are not added to the placeholder. Dynamically added control should be added on each postback. My recommendation is to store a counter in a variable and at your page load, add your web controls again depending to this counter.

Related Solutions

ASP.Net: User controls added to placeholder dynamically cannot retrieve values

This is based on .NET v1 event sequence, but it should give you the idea:

Initialize (Init event)
Begin Tracking View State (checks if postback)
- Load View State (if postback)
- Load Postback Data (if postback)
Load (Load event)
- Raise Changed Events (if postback)
- Raise Postback Events (if postback)
PreRender (PreRender event)
Save View State
Render
Unload (Unload event)
Dispose

As you can see, the loading of ViewState data back to the controls happen before the Load event. So in order for your dynamically-added controls to "retain" those values, they have to be present for the ASP.NET page to reload the values in the first place. You would have to re-create those controls at the Init stage, before Load View State occurs.

Jquery – ASP.NET + jQuery + Dynamically Created HyperLink controls

What you're trying to do isn't possible that way. You create links every time the page is created. Although you change the name of these links in JavaScript, these values are not posted back to you.
On Sumbit, only form elements get posted back to the server (<input>s, for example), not <a> elements, so your server doesn't "know" the changes were made.

Secondly, even if you'll change the <a>s to <input>s, you still have a problem: you won't be able to find these values in reportTable.Rows[0].Cells as you expect. Normally asp.net will fill these values correctly, even for dynamically generated controls, but not here - since you've changed their names! Asp.net cannot rebind these values.

So, what should you do? One option is to add an hidden field to every cell.
On AddLinkButtonToRow, add the following:

HtmlInputHidden hidden = new HtmlInputHidden();
hidden.ID = "hidden" + linkButton.ID;
hidden.Name = hidden.ID; //so it will be posted!
hidden.Style["display"] = "none"; //better to have a CssClass

Using jQuery, which you seem to know, change the values of these input fields, not their names (something like $(editingID).parent().find(":hidden")).

Next, you might not see the values on the controls, but you can find them at Request.Form["hiddenh1"] ... Request.Form["hiddenh11"] - All input fields will names will be posted, and you know their names this time.

Best Answer

Related Solutions

ASP.Net: User controls added to placeholder dynamically cannot retrieve values

Jquery – ASP.NET + jQuery + Dynamically Created HyperLink controls

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