It is possible to subscribe to events with anonymous delegates, but having done so, it is impossible to unsubscribe from them. That’s because the
process of subscribing adds the delegate to a list. The process of unsubscribing essentially says: remove this item from the subscription
list. But because an anonymous delegate was used in both cases, the unsubscribe attempt tries to remove a different item from the list than was added.
Instead, save the delegate to a variable and use the variable to subscribe and unsubscribe.
Noncompliant Code Example
listView.PreviewTextInput += (obj,args) =>
listView.PreviewTextInput -= (obj, args) =>
listView_PreviewTextInput(obj, args, listView); // Noncompliant; this delegate was never subscribed
EventHandler func = (obj,args) => listView_PreviewTextInput(obj,args,listView);
listView.PreviewTextInput += func;
listView.PreviewTextInput -= func;