Single instance Child form not working

Question

4.00/5 (1 vote)

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frmSChild objfrmSChild = frmSChild.GetChildInstance();
objfrmSChild.MdiParent = this;
objfrmSChild.Show();
objfrmSChild.BringToFront();

It is working fine. But it only works once.

I open the that frmSChild for 2 or 3 times. it will bring forwards that form.
But if I close that form and open again. there is an error stating "Cannot access a disposed object. Object name: 'frmSChild..."
How to modify the code to get it done?

Posted 4-Jun-11 1:02am

Ragi Gopi

Updated 4-Jun-11 1:59am

Michael Waguih

v3

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Ragi Gopi 4-Jun-11 7:06am

error "Cannot access a disposed object. Object name: 'frmSChild..."

4 solutions

Solution 1

That is because objfrmSChild Form is Closed[^].

When Close method is called. All resources created within the object are closed and the form is disposed.

What happens in GetChildInstance ?

Posted 4-Jun-11 1:19am

Kim Togo

Comments

Ragi Gopi 4-Jun-11 7:23am

can u plz suggest me a solution for that....

Kim Togo 4-Jun-11 8:50am

It is a bet hard to do that. I have to see what GetChildInstance method is doing. Can you press "Improve question" and tell us what GetChildInstance do ?

Solution 2

I have alread answered this question here[^], including explaining why your disposed object no longer exists.

Given some of your comments it appears that you have been following some step by step guide without really understanding what is going on in the code. I suggest you take a look at the MSDN documentation on disposing[^].

Also, please do not start a new thread with exactly the same question but add some more detail to the original.

Posted 4-Jun-11 2:52am

Richard MacCutchan

Solution 3

Just in case anyone was wondering, this is the author's text in the article he is following, just to reveal the GetChildInstance() method for everyone... just meant to keep user from opening more than 1 of that form at a time.

OP, as others have said, your problem has to do with how the child form is closed and disposed, and how the frmSChild handles it's instance check below to be created for the parent... I would submit your issue on the article page to the author can help you remedy the logic.

Putting life in the menus created by adding code to it
--------------------------------------------------------
1> Now in the frmSChild code add the following lines

  private static frmSChild m_SChildform;
  public static frmSChild GetChildInstance()
  {
   if (m_SChildform ==null) //if not created yet, Create an instance
    m_SChildform = new frmSChild();
   return m_SChildform;  //just created or created earlier.Return it
  }
//This is to make sure that when we Click on a 'New Single' menu on Parent form twice 
//it should not open two instance of the same child form

Posted 4-Jun-11 6:16am

fcronin

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Valery Possoz · Accepted Answer · 2011-06-04T06:31:00

hello,

here is a good article showing how to implement the singleton pattern for MDI forms:
Singleton pattern for MDI child forms[^]

one of the important bit is how to dispose of the form:

C#

protected override void Dispose( bool disposing )
{
    if( disposing )
    {
        if(components != null)
        {
            components.Dispose();
        }
    }
    base.Dispose( disposing );
    m_SChildform = null;
}

Valery.