HELP: can you trap a Forms closed() event??

[PGAMMER]

I have an MDI application and when I click a menu it loads a form, but if you click the menu again it loads the same form again. It might corrupt my memory so I need to only allow one instance of the form. If the form is already loaded I just want it to BrintToFront() the form. I have tried several ways but nothing seems to work aside from using a global variable which I don't like to do.

Is there a way to trap the forms Closed() event so I can tell when it was closed, or is there a way to use a reference counter? Does someone have a code example of how to do this?

Thanks.

P.S. I don't want to do the hack that disables the menu item when the form is loaded, I don't like that. I want the user to still be able to click the menu item, and BringToFront() the form.

Basically, I need to know how to have the mdi child form tell its parent form when its been unloaded.

Thanks!

[hedge_fund]

Instead of making the form variable global, why don't you make it a private member of the mdiparent and then add a function like LoadChildForm to which you could pass the type of the form you are checking if it exists? The function could check your member variable to see if it's null or if it has been disposed, and if so, then it would allocate a new form. If it does not need to be allocated, you could simply call BringToFront on the member variable.

Something like below...

void LoadChildForm(Type tp)
{
    switch(tp.ToString())
{
        case "AboutForm":
        if(this.m_frmAbout == null || this.m_frmAbout.IsDisposed)
             this.m_frmAbout = new AboutForm();
        this.m_frmABout.BringToFront();
        break;
}
} 

[aniskhan]

function checks whether new form object is a part of mdiChildern collection ,if it is the don't create new instance of the form.

void chk(Form frm) 
{ 
 Form f; 
 foreach (int f in this.MdiChildren) { 
   if (((Form)(f)).Name == frm.Name) { 
     frm.Close(); 
return; 
   } 
 } 
 frm.MdiParent = this; 
 frm.Show(); 
}

[PGAMMER]

I cant get either one to work. The first one doesn't do anything when I click the menu item. I don't know.

[hedge_fund]

Well, why dont you show us then what you have tried that it does not work? It's difficult to help when we don't see your code.

[MadHatter]

in your mdi parent, you have to initialize the child window. you have a collection of MDI Children that you can check before creating the new window. if it already exists, than you can bring it to the front.

there is a Closing event on the form that you can attach to as well.

[pankajs]

hi

You can easily trap the form close event.
For this you have to write your own event handler for form close event and in that event handler you can do what ever you want.

int the code form of which you want to trap the close event write following

In the event declearation block where the events are decleared for button and for every control write this line

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

By declearing this you are calling DoSomething method when you close the form now define the method.


private void DoSomething(object sender, System.ComponentModel.CancelEventArgs e)
{
// now you can continue doing what you want
}

here you can keep some flag which will be set or reset when form close.

[bewa]

Why don't you go for the simple solution? Just add for each child form a boolean in de MDI parent. Then when the user clicks the menu item or whatever you check for that boolean you just code for example:

if ( m_bChildForm1IsOpened )
{
//do code to maximize ChildForm1
}
else
{
//do code for opening the form.
bChildForm1IsOpened = true;
}

edit:
Having reread my post, I realise how quick and dirty this is. However, I have used this before and it works great.