C# Winform MDI Form with Split Container - MdiChildren is empty-CodePudding

I am creating a C# .Net 4.8 Winform app with one MDI Form. This MDI Form has several panels and a split container.

When adding a childform I use the following code:

frm.Text = formTitleText;
frm.MdiParent = this;
frm.TopLevel = false;
frm.FormBorderStyle = FormBorderStyle.None;
frm.Dock = DockStyle.Fill;
panelDeskTop.Controls.Add(frm);
panelDeskTop.Tag = frm;
frm.BringToFront();
lblTitleChildForm.Text = $"{frm.Text}({this.MdiChildren.Length})";
frm.Show();

The form shows in the panel, but is not added as a MDI Child. The Parent (This) is the MDI Parent and has property of IsMDIContainer. So the this.MdiChildren.Length is always 0.

Not sure why?

Thanks in advance.

CodePudding user response：

It's expected. You've set another parent for it: panelDeskTop.Controls.Add(frm);.

Consider the following points:

An MDI parent form has a control of type