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

c# invalidoperationexception
Brandon picture Brandon · Jul 14, 2011 · Viewed 14.3k times · Source

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

Jin-Wook Chung picture Jin-Wook Chung · Jul 14, 2011

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.

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