Drag and Drop and single click style. Why did it work TWICE?

my application uses Drag & Drop operations. Everything worked perfect. Recently, some user changed system options:

Control Panel --> Folder Options --> Single click to open an item (point to select).

And now all my drag & drop开发者_如何学运维 operations worked TWICE. How could it be ? What should I change to avoid that type of behaviour ?

Check this thread: C# ListView DragDrop Event Method Executing Twice Per Drop

This usually happens if you added the event handlers yourself, by hand, and then double-clicked (e.g.) the event in the designer assuming all that does is create an empty method to put your code in. It does but it also adds the very same event handlers in the XYZ.Designer.cs file.