Collection was modified enumeration operation may not execute.

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i want to avoid More than one child windows form open in my application in mdi from.
i make a component for that it has method to do this when i calling a method the runtime error occur. error is as
'Collection was modified enumeration operation may not execute.'
the code is as

C#

if (checkopen0 == 1)
          {
              MessageBox.Show("Already Open");
              return;
          }

              closeForm1.CloseAllOpenForm(this);



          StudentMaster frm = new StudentMaster();
          frm.MdiParent = this;
          frm.Show();
          checkopen0 = 1;

the code for component class is as

MIDL

public partial class CloseForm : Component
{
    public CloseForm()
    {
        InitializeComponent();
    }

    public CloseForm(IContainer container)
    {
        container.Add(this);

        InitializeComponent();
    }
    public void CloseAllOpenForm(Form CurForm)
    {
        lock (CurForm)
        {
            foreach (Form frm in System.Windows.Forms.Application.OpenForms)
            {

                if (!(CurForm.Equals(frm)))
                {
                    frm.Close();
                }
            }
        }

    }
}

plz help me to solve this error
and sory for poor english.
thanks in advance.

Posted 2-Mar-10 22:35pm

Yogesh M Patil

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Nicholas Butler · Accepted Answer · 2010-03-02T22:54:00

You cannot alter an enumeration while iterating over it.

You can create a temporary collection of matching forms and then iterate over that collection and close them:

C#

public void CloseAllOpenForm( Form currentForm )
{
    // temp list
    var list = new List<Form>();

    // fill list
    foreach ( Form form in Application.OpenForms )
        if ( !currentForm.Equals( form ) )
            list.Add( form );

    // close selected forms
    foreach ( Form form in list )
        form.Close();
}

Nick