About PropertyStore and MDI child form.

Question

This is .net WinForm question about MDI setting.

When the main form creates an MDI child form, the main form's PropertyStore holds a reference to the MDI child form. I wonder whether this will cause the child form to be alive even if it is closed. If so, what shall I do when disposing the child form in order to remove this reference?

The child form is called by sample code:

//The code is in the main form.
var f = new FormMDIChild();
f.MdiParent = this;
f.Show();

Answer 1

I'm having a similar problem. I found this forum post discussing the issue and suggesting a solution however I'm not sure if this property has been removed in recent service packs as I can't seem to find the property using reflection so the solution isn't working for me. I'll keep looking around and let you know if I find another solution.

Answer 2

For the record, the solution offered in the referenced post does work (though it's a little dicey). However, the leak also goes away if you open and close another child form, it appears that the MDI Parent only leaks the last opened child.

If you want to fix the leak by using the work around mentioned in the referenced post, just override the MDIParent's OnMdiChildActivate method...

protected override void OnMdiChildActivate(EventArgs e)
{
    base.OnMdiChildActivate(e);

    typeof(Form).InvokeMember("FormerlyActiveMdiChild", 
        BindingFlags.Instance | BindingFlags.SetProperty |
        BindingFlags.NonPublic, null, this, new object[] { null });
}