subclass a programmatically created NSImage - subclass

Question

I programatically create an NSImage like this:
NSImageView *IconBox = [[NSImageView alloc] initWithFrame:CGRectMake(0, 0, 350, 300)];
NSImage *capper = [[NSImage alloc] initWithData:[self.superview dataWithPDFInsideRect:[self.superview bounds]]];
IconBox.image = capper;
[self addSubview:IconBox];
This Image gets main Part of my Window and i want to make this window draggable anywhere, i know i need to set mouseDownCanMoveWindow, but this doesn't work, while this applies to the Windoow, but while my Image is the main visible part of the Window you cannot access its background, so i need to tell the Image to drag the Window,
i read i need to subclass the NSImage and override this Method, but how can i subclass a programatically created NSImage?
I already created the Class Files in my Project, but how can i tell the newly created Image to use this custom class?

Answer 1

Figured it out:
Class snap = NSClassFromString(#"snapper");
object_setClass(IconBox, [snap class]);
This does the trick, also ithe default Method moveWindowByMouseDown didn't work either, but this snippet did:
In the NSImage Subclass:
-(void)mouseDragged:(NSEvent *)theEvent
{
CGFloat deltax = [theEvent deltaX];
CGFloat deltay = [theEvent deltaY];
NSRect frame = [[self window] frame];
frame.origin.x += deltax;
frame.origin.y -= deltay;
[[self window] setFrameOrigin:frame.origin];
}