Question

I have a webpage containing a panel and a button. When you click the button, I want to add a new instance of a UserControl to the panel.

The panel.Controls.Add method specifies that it adds an item to a collection.

I can do this using a local variable to store the number of instances of the control. Then when one it added it loops this many times creating new controls.

private void AddUCToUI(int counter)
    {
        for (int i = 0; i < counter; i++)
        {
            MyControl ctrlMyControl = (MyControl)LoadControl("MyControl.ascx");
            ctrlMyControl.SetID(i);
            myPanel.Controls.Add(ctrlMyControl);
        }
    }

BUT, I don’t want to recreate all of the controls every time, as the user may have already entered data into them…

So all I want to do is create another control, and add it to the collection which already contains the first one.

private void AddUCToUI(int counter)
    {
        MyControl ctrlMyControl = (MyControl)LoadControl("MyControl.ascx");
        ctrlMyControl.SetID(counter);
        myPanel.Controls.Add(ctrlMyControl);
    }

This should create a new control, give it an ID, then add it to the collection. However it seems to add a control in the first instance, then overwrite this control in the collection when I attempt to add another. Why is this?

Answer 1

I have managed to solve this issue:

Moving the code from onInit to Page_Load and using a session variable for counter solved the issue of incrementing it’s value. Session variables are not reset when a PostBack happens.

Here is my solution:

protected override void Page_Load(object sender, EventArgs e)
{
    int counter;

    if (Session["counter"] == null)
    {
        counter = 0;
    }
    else
    {
        counter = (int)Session["counter"];
    }

    for (int i = 0; i < counter; i++)  
    {  
        MyControl ctrlMyControl = (MyControl)LoadControl("MyControl.ascx");  
        ctrlMyControl.ID = String.Format("ctrl_{0}", myPanel.Controls.Count); //count = 0
        myPanel.Controls.Add(ctrlMyControl); //count = 1
    }      
}