如何在不使用e.Handled = true的情况下防止两次调用Closing事件？

Question

I have a handler for Closing event of a tab, it shows a confirm closing message. if the user choose No , I set e.Handled = true; but if he chooses Yes close, I remove the tab from the tab list and do other stuff, when the method reaches its end, it then get called again, showing the same message, I tried to set e.Handled = true; in the end of the method but the tab doesn't close.

void oTab_TabClosing(object sender, RoutedEventArgs e)
{
    var close = MainClass.ShowMessage(ResCommon.MsgConfirmClose, ResCommon.ttlClose, MainClass.MessageButtons.YesNO);
    if (!close)
    {
        e.Handled = true;
        return;
    }
    FabTab.FabTabItem oTabItem = (FabTab.FabTabItem)sender;
    if (HtOpenTabs.ContainsKey(oTabItem.Name)) HtOpenTabs.Remove(oTabItem.Name);
    oTabItem = null;

    GC.Collect();
    GC.WaitForPendingFinalizers();
}

This method subscribe to the event:

public void AddToTab(object formToOpen, string formTitle)
{
    string formName = ((UserControl)formToOpen).Name;
    if (HtOpenTabs.ContainsKey(formName))
    {
        // By Yousef Mohamed (12-10-2014) - Activate opened tab //
        foreach (FabTabItem item in ((FabTabControl)this.tabControl).Items)
        {
            if (item.Name == formName)
            {
                ((FabTabControl)this.tabControl).SelectedItem = item;
                return;
            }
        }
    }

    var oTab = new FabTabItem { Content = formToOpen };
    oTab.Name = formName;
    oTab.TabClosing += oTab_TabClosing;

    oTab.Header = formTitle;
    BrushConverter bc = new BrushConverter();
    Brush brush = (Brush)bc.ConvertFrom("#FFF0F8FF");
    brush.Freeze();
    oTab.Background = brush;
    oTab.Height = 30;
    tabControl.Items.Add(oTab);
    tabControl.SelectedIndex = tabControl.Items.Count - 1;
    HtOpenTabs.Add(formName, oTab);
}

Answer 1

It seems that second event is fired in the HtOpenTabs.Remove(oTabItem.Name);

Try to unsubscribe this event handler before removing your tab.