Programmatically selecting an existing TabPage in a TabControl shows a blank page

Question

I use this method to create a new TabPage in a TabControl (TabManager) if a TabPage with the specified text doesn't exist, or just select it if it already exists:

private void AddControls(UserControl uc, string TabCaption)
{           
    Boolean TabFound = false;
    if (TabManager.TabCount == 0)
    {
        TabPage tp = new(TabCaption);
        TabManager.TabPages.Add(tp);
        uc.Dock = DockStyle.Fill;
        tp.Controls.Add(uc);
        TabManager.SelectedTab = tp;               
    }
    else
    {
        TabPage tp = new(TabCaption);
        foreach (TabPage tp1 in TabManager.TabPages)
        {
            
            if (tp1.Text == TabCaption)
            {
                TabFound = true;
            }                  
        }
        if (TabFound != true)
        {                    
            TabManager.TabPages.Add(tp);
            uc.Dock = DockStyle.Fill;
            tp.Controls.Add(uc);
            TabManager.SelectTab(tp);
            //tp.Show();
            //tp.BringToFront();
        }
        else
        {
            TabManager.SelectedTab = TabManager.TabPages[tp.Name];                   
            return;
        }
    }            
}

The problem is that the TabPage is not selected, instead an empty page is shown.

The offending code appears to be:

 TabManager.SelectedTab = TabManager.TabPages[tp.Name]; 

As it will only show an empty TabPage.
I searched for documentation but found no solution so far.

Answer 1

If you create a new TabPage with the provided text (as in TabPage tp = new(TabCaption);), your tp object is not the same as an existing TabPage with the same Caption, so TabManager.SelectTab(tp); won't select it (not the same object).

You see a blank background because when you use the TabControl.SelectedTab() method and the TabPage specified doesn't exist, no TabPage is the Current, so you just see the TabControl background.

---

To determine whether to add or just select a TabPage, you can check whether the TabControl has no TabPages (as you're doing) and also verify whether a TabPage with the same Name already exists.
You can use the TabPageCollection.IndexOfKey() method to perform this check.

You should assign a Name to your new TabPage, not just a Caption, as it happens when you create a new TabPage in the Designer.

This simplifies the creation and/or selection of TabPages. Your code could then be:

private void AddControls(Control uc, string tabCaption)
{
    if (TabManager.TabCount == 0 || TabManager.TabPages.IndexOfKey(tabCaption) < 0) {
        var tp = new TabPage(tabCaption);
        // or TabPage tp = new(tabCaption);
        tp.Name = tabCaption;
        uc.Dock = DockStyle.Fill;
        tp.Controls.Add(uc);
        TabManager.TabPages.Add(tp);
            
    }
    TabManager.SelectedTab = TabManager.TabPages[tabCaption];
}