C# System.InvalidOperationException: Collection was modified; enumeration operation may not execute

Question

I have researched this issue and haven't found what pertains to me yet. I am not trying to edit something I am looping through.

************** Exception Text **************
System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource)
at System.Collections.Generic.List`1.Enumerator.MoveNextRare()
at System.Collections.Generic.List`1.Enumerator.MoveNext()

Here is my function that is causing it:

internal static bool CloseAllForms()
{
    try
    {
        if (clsGlobal.g_objfrmCustomerInformation != null)
            clsGlobal.g_objfrmCustomerInformation.Close();
        if (clsGlobal.g_objfrmSearchCustomer != null)
            clsGlobal.g_objfrmSearchCustomer.Close();

        if (clsGlobal.g_objfrmSwipeLicense != null)
            clsGlobal.g_objfrmSwipeLicense.Close();

        if (clsGlobal.g_objfrmSearchResults != null)
            clsGlobal.g_objfrmSearchResults.Close();

        if (clsGlobal.g_objfrmCustomerData != null)
            clsGlobal.g_objfrmCustomerData.Close();
        if (clsGlobal.g_objfrmPurchaseOrder != null)
            clsGlobal.g_objfrmPurchaseOrder.Close();
        if (clsGlobal.g_objfrmAddPurchaseOrderItem != null)
            clsGlobal.g_objfrmAddPurchaseOrderItem.Close();
        if ((clsGlobal.g_objfrmCustomerInformation == null) && (clsGlobal.g_objfrmSearchCustomer == null) && (clsGlobal.g_objfrmSwipeLicense == null) && (clsGlobal.g_objfrmSearchResults == null) && (clsGlobal.g_objfrmCustomerData == null) && (clsGlobal.g_objfrmPurchaseOrder == null) && (clsGlobal.g_objfrmAddPurchaseOrderItem == null))
        {
            PrepareImageBar();
            return true;
        }
        else
        {
            PrepareImageBar();
            return false;
        }
    }
    catch (Exception ex)
    {
        string ErrorMessage;

        ErrorMessage = "Error: " + ex.Message +
           "\r\nSource: " + ex.Source +
           "\r\nTargetSite: " + ex.TargetSite.ToString() +
           "\r\nStackTrace: " + ex.StackTrace.ToString();

        if (ex.Data.Count > 0)
        {
            ErrorMessage += "\r\nData Count: " + ex.Data.Count.ToString() +
                "\r\nKeys: " + ex.Data.Keys.ToString() +
                "\r\nValues: " + ex.Data.Values.ToString();
        }

        MessageBox.Show(ErrorMessage, "", MessageBoxButtons.OK, MessageBoxIcon.Error);
        CustomFunctions.emailExceptionToAuthor(ex);

        return false;
    }
}

This is how I call the function:

if (CloseAllForms())
{
    if (clsGlobal.g_objfrmPurchaseOrder == null)
    {
        clsGlobal.g_objfrmPurchaseOrder = new frmPurchaseOrder();

        clsGlobal.g_objfrmPurchaseOrder.FormClosed += PurchaseOrderFormClosed;
        clsGlobal.g_objfrmPurchaseOrder.MdiParent = clsGlobal.g_objfrmMDIMain;
        clsGlobal.g_objfrmPurchaseOrder.Show();
        clsGlobal.g_objfrmPurchaseOrder.BringToFront();
    }
    else
    {
        clsGlobal.g_objfrmPurchaseOrder.Show();
        clsGlobal.g_objfrmPurchaseOrder.BringToFront();
    }

    PrepareImageBar();
}

Please help me!

UPDATE: Here is the full code.

The exception See the end of this message for details on invoking just-in-time (JIT) debugging instead of this dialog box.

************** Exception Text **************
System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource)
at System.Collections.Generic.List`1.Enumerator.MoveNextRare()
at System.Collections.Generic.List`1.Enumerator.MoveNext()
at Microsoft.VisualBasic.PowerPacks.ShapeCollection.Dispose(Boolean disposing)
at Microsoft.VisualBasic.PowerPacks.ShapeContainer.Dispose(Boolean disposing)
at System.ComponentModel.Component.Dispose()
at System.Windows.Forms.Control.Dispose(Boolean disposing)
at System.Windows.Forms.Form.Dispose(Boolean disposing)
at B2HD_Software.frmCustomerData.Dispose(Boolean disposing)
at System.Windows.Forms.Form.WmClose(Message& m)
at System.Windows.Forms.Form.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

PrepareImageBar();

internal static void PrepareImageBar()
{
clsGlobal.g_objfrmMDIMain.mnuImageBarAddCustomer.Visible = false;
clsGlobal.g_objfrmMDIMain.mnuImageBarAddCustomer.Enabled = true;
clsGlobal.g_objfrmMDIMain.mnuImageBarEditCustomer.Visible = false;
clsGlobal.g_objfrmMDIMain.mnuImageBarEditCustomer.Enabled = true;
clsGlobal.g_objfrmMDIMain.mnuImageBarFindCustomer.Visible = false;
clsGlobal.g_objfrmMDIMain.mnuImageBarFindCustomer.Enabled = true;
clsGlobal.g_objfrmMDIMain.mnuImageBarStartSearch.Visible = false;
clsGlobal.g_objfrmMDIMain.mnuImageBarStartSearch.Enabled = false;
clsGlobal.g_objfrmMDIMain.mnuImageBarSwipeLicense.Visible = false;
clsGlobal.g_objfrmMDIMain.mnuImageBarSwipeLicense.Enabled = true;
clsGlobal.g_objfrmMDIMain.mnuImageBarViewNotes.Visible = false;
clsGlobal.g_objfrmMDIMain.mnuImageBarViewNotes.Enabled = true;
clsGlobal.g_objfrmMDIMain.mnuImageBarNewPurchase.Visible = false;
clsGlobal.g_objfrmMDIMain.mnuImageBarNewPurchase.Enabled = true;
clsGlobal.g_objfrmMDIMain.mnuImageBarAddItem.Visible = false;
clsGlobal.g_objfrmMDIMain.mnuImageBarAddItem.Enabled = true;
clsGlobal.g_objfrmMDIMain.mnuImageBarModifyItem.Visible = false;
clsGlobal.g_objfrmMDIMain.mnuImageBarModifyItem.Enabled = false;
clsGlobal.g_objfrmMDIMain.mnuImageBarDeleteItem.Visible = false;
clsGlobal.g_objfrmMDIMain.mnuImageBarDeleteItem.Enabled = false;
clsGlobal.g_objfrmMDIMain.mnuImageBarTakePicture.Visible = false;
clsGlobal.g_objfrmMDIMain.mnuImageBarTakePicture.Enabled = true;
clsGlobal.g_objfrmMDIMain.mnuImageBarSavePicture.Visible = false;
clsGlobal.g_objfrmMDIMain.mnuImageBarSavePicture.Enabled = true;
clsGlobal.g_objfrmMDIMain.mnuImageBarSave.Visible = false;
clsGlobal.g_objfrmMDIMain.mnuImageBarSave.Enabled = true;
clsGlobal.g_objfrmMDIMain.mnuImageBarCancel.Visible = false;
clsGlobal.g_objfrmMDIMain.mnuImageBarCancel.Enabled = true;
clsGlobal.g_objfrmMDIMain.mnuImageBarAdmin.Visible = false;
clsGlobal.g_objfrmMDIMain.mnuImageBarAdmin.Enabled = true;

switch (clsGlobal.ActiveForm())
{
    case "CustomerInformation":
        clsGlobal.g_objfrmMDIMain.mnuImageBarTakePicture.Visible = true;
        clsGlobal.g_objfrmMDIMain.mnuImageBarSave.Visible = true;
        clsGlobal.g_objfrmMDIMain.mnuImageBarCancel.Visible = true;
        clsGlobal.g_objfrmMDIMain.mnuImageBarCancel.Enabled = true;

        break;
    case "SearchCustomer":
        clsGlobal.g_objfrmMDIMain.mnuImageBarStartSearch.Visible = true;
        clsGlobal.g_objfrmMDIMain.mnuImageBarSwipeLicense.Visible = true;
        clsGlobal.g_objfrmMDIMain.mnuImageBarCancel.Visible = true;
        clsGlobal.g_objfrmMDIMain.mnuImageBarStartSearch.Enabled = false;

        break;
    case "SwipeLicense":
        clsGlobal.g_objfrmMDIMain.mnuImageBarCancel.Visible = true;

        break;
    case "CustomerData":
        clsGlobal.g_objfrmMDIMain.mnuImageBarCancel.Visible = true;
        clsGlobal.g_objfrmMDIMain.mnuImageBarViewNotes.Visible = true;
        clsGlobal.g_objfrmMDIMain.mnuImageBarNewPurchase.Visible = true;
        clsGlobal.g_objfrmMDIMain.mnuImageBarEditCustomer.Visible = true;

        break;
    case "PurchaseOrder":
        clsGlobal.g_objfrmMDIMain.mnuImageBarCancel.Visible = true;
        clsGlobal.g_objfrmMDIMain.mnuImageBarAddItem.Visible = true;
        clsGlobal.g_objfrmMDIMain.mnuImageBarDeleteItem.Visible = true;
        clsGlobal.g_objfrmMDIMain.mnuImageBarModifyItem.Visible = true;
        clsGlobal.g_objfrmMDIMain.mnuImageBarEditCustomer.Visible = true;
        clsGlobal.g_objfrmMDIMain.mnuImageBarViewNotes.Visible = true;

        clsGlobal.g_objfrmPurchaseOrder.ShowProperButtons();

        break;
    case "AddPurchaseOrderItem":
        clsGlobal.g_objfrmMDIMain.mnuImageBarTakePicture.Visible = true;
        clsGlobal.g_objfrmMDIMain.mnuImageBarSave.Visible = true;
        clsGlobal.g_objfrmMDIMain.mnuImageBarCancel.Visible = true;
        clsGlobal.g_objfrmMDIMain.mnuImageBarViewNotes.Visible = true;

        break;

    default:
        clsGlobal.g_objfrmMDIMain.mnuImageBarAddCustomer.Visible = true;
        clsGlobal.g_objfrmMDIMain.mnuImageBarFindCustomer.Visible = true;
        clsGlobal.g_objfrmMDIMain.mnuImageBarSwipeLicense.Visible = true;

        break;
}
}

CloseAllForms()

internal static bool CloseAllForms()
{
if (clsGlobal.g_objfrmCustomerInformation != null)
    clsGlobal.g_objfrmCustomerInformation.Close();

if (clsGlobal.g_objfrmSearchCustomer != null)
    clsGlobal.g_objfrmSearchCustomer.Close();

if (clsGlobal.g_objfrmSwipeLicense != null)
    clsGlobal.g_objfrmSwipeLicense.Close();

if (clsGlobal.g_objfrmSearchResults != null)
    clsGlobal.g_objfrmSearchResults.Close();

if (clsGlobal.g_objfrmCustomerData != null)
    clsGlobal.g_objfrmCustomerData.Close();

if (clsGlobal.g_objfrmPurchaseOrder != null)
    clsGlobal.g_objfrmPurchaseOrder.Close();

if (clsGlobal.g_objfrmAddPurchaseOrderItem != null)
    clsGlobal.g_objfrmAddPurchaseOrderItem.Close();

if ((clsGlobal.g_objfrmCustomerInformation == null) && (clsGlobal.g_objfrmSearchCustomer == null) && (clsGlobal.g_objfrmSwipeLicense == null) && (clsGlobal.g_objfrmSearchResults == null) && (clsGlobal.g_objfrmCustomerData == null) && (clsGlobal.g_objfrmPurchaseOrder == null) && (clsGlobal.g_objfrmAddPurchaseOrderItem == null))
{
    PrepareImageBar();
    return true;
}
else
{
    PrepareImageBar();
    return false;
}

}

This is what my close event looks like on each form.

internal static void CustomerInformationFormClosed(object sender, FormClosedEventArgs e)
    {
        clsGlobal.g_objfrmCustomerInformation = null;

        PrepareImageBar();
    }

Answer 1

I've seen this bug: The error apparently only shows up on some windows installs, and I've never gotten it to occur in the development environment via debug, only the full app.

This is a bug in the VisualBasic.PowerPacks.

See here for a solution (see the end of the blog).

You basically have to override the forms Dispose() method and manually dispose of all VisualBasic Powerpack items.

Answer 2

I see three possibilities:

1. Something is failing in the FormClosed event handler for one of the forms (i.e., maybe something in PurchaseOrderFormClosed).
2. Your CloseAllForms() method is doing a bunch of work in the catch. It could be possible that the code is failing there. When the error occurs, do you see the MessageBox? Does the email get sent? Try commenting out all of the code there and see if you still get the error. Or maybe just temporarily replace all of the code in the catch with a MessageBox.Show(ex.ToString()) so you can be sure the exception you are seeing is occurring in the try.
3. Something is failing in PrepareImageBar(). Try commenting out that method and see if you still get the error.

Answer 3

I don't know where the exception was occurred but the exception might be generated in foreach code block where the collection was modified. Here, the modification means 'Add' or 'Remove' something like:

foreach(var item in collection)    { collection.Add(other);}

A collection cannot be modified while enumerating.

---

UPDATED

To find where it was occurred if being in your code, while debugging, you would check the 'user unhandled option' in Exceptions dialog (Ctrl+Alt+E). However, please note that to use this option, VS has to be set 'Enable just My Code' in Debugging option.