How to deal with GetDataPresent to let it accept all the derived types

I'm using drgevent.Data.GetDataPresent to determine whether the dragged component is acceptable or not.

I've got a problem which is that I want to accept a specific type say SomeType and all the types that derived from it. Seems GetDataPresent doesn't support such requirement.

Any idea?

Solution

Just don't use GetDataPresent(), it is boilerplate but you're free to do it your way. Actually retrieve the object and check if you're happy with its type:

    protected override void OnDragEnter(DragEventArgs drgevent) {
        var obj = drgevent.Data.GetData(drgevent.Data.GetFormats()[0]);
        if (typeof(Base).IsAssignableFrom(obj.GetType())) {
            drgevent.Effect = DragDropEffects.Copy;
        }
    }

Where Base is the name of the base class. While the use of GetFormats() looks odd, this approach is guaranteed to work because dragging a .NET object only ever produces one format, the display name of the type of the object. Which is also the reason that GetDataPresent can't work for derived objects.