https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.toolbar.toolbarbuttoncollection.system-collections-ilist-contains?view=netframework-4.8.1&viewFallbackFrom=windowsdesktop-10.0
ToolBar.ToolBarButtonCollection.IList.Contains(Object) Method (System.Windows.Forms) | Microsoft...
Determines whether the collection contains a specific value.
windows formstoolbarilistcontainsobject