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I've added this line in my main dialog: 
 
note.Closing += new System.ComponentModel.CancelEventHandler(this.NoteFormClosing); 
 
and added a event handler: 
 
void NoteFormClosing(object sender, System.ComponentModel.CancelEventArgs e) 
{ 
&nbsp; noteObjects.Remove(sender); 
} 
 
It works fine. Thank you AlexFM!
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I've added this line in my main dialog:

note.Closing += new System.ComponentModel.CancelEventHandler(this.NoteFormClosing);

and added a event handler:

void NoteFormClosing(object sender, System.ComponentModel.CancelEventArgs e)
{
  noteObjects.Remove(sender);
}

It works fine. Thank you AlexFM!

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I've got a main dialog, which itself creates new dialogs. Every time I create a new dialog, I do this: 
 
NoteForm note = new NoteForm(); 
noteObjects.Add(note); 
note.Show(); 
 
That means that I save a reference to the dialog in an ArrayList called noteObjects. The dialogs can be minimized and hidden. I added a button in my main dialog that shows all dialogs. So what I do is iterating through the ArrayList and call: 
 
for(i=0;i&lt;noteObjects.Count;i++) { 
((NoteForm)noteObjects[i]).Show(); 
} 
 
If a dialog has been closed, there are invalid entries in the array which cause a System.ObjectDisposedException 
 
How can I remove array elements that have become invalid? 
if ((NoteForm)noteObjects[i] == null) ... doesn't work. 
 
Thanks for any suggestion, 
Martin
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I've got a main dialog, which itself creates new dialogs. Every time I create a new dialog, I do this:

NoteForm note = new NoteForm();
noteObjects.Add(note);
note.Show();

That means that I save a reference to the dialog in an ArrayList called noteObjects. The dialogs can be minimized and hidden. I added a button in my main dialog that shows all dialogs. So what I do is iterating through the ArrayList and call:

for(i=0;i<noteObjects.Count;i++) {
((NoteForm)noteObjects[i]).Show();
}

If a dialog has been closed, there are invalid entries in the array which cause a System.ObjectDisposedException

How can I remove array elements that have become invalid? 
if ((NoteForm)noteObjects[i] == null) ... doesn't work.

Thanks for any suggestion,
Martin

Check if object still exists

C# is an object-oriented programming language created in conjunction with Microsoft’s .NET framework. Compilation is usually done into the Microsoft Intermediate Language (MSIL), which is then JIT-compiled to native code (and cached) during execution in the Common Language Runtime (CLR).