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Re: Delegate methods for NSImageView (?)

On Friday, December 6, 2002, at 07:08 PM, email@hidden wrote:

I need to popup a warning message to user's when certain types of images are dropped into an NSImageView (via drag & drop)... or, possibly, just prevent the drop at all if the image type is not one I intend to support. I was at first expecting there would be a simple delegate method or NSNotification for the drop event which would provide my controller a chance to manage this. However, looking at the documentation, I see no such methods/notifications. I'm sure I'm missing something obvious... what's the best way to handle this?


Eric,

The way I did this was to subclass NSImageView. In the subclass, I implemented the methods I needed from the DragDestination informal protocol, mainly -draggingEntered:, -draggingExited:, and -performDragOperation:[

<http://developer.apple.com/techpubs/macosx/Cocoa/Reference/ ApplicationKit/ObjC_classic/Protocols/NSDraggingDestination.html>

In my draggingEntered: implementation, I filter dropped URLs (I'm accepting drags from the Finder) by file extension. If the URL doesn't have the right file extension, I don't handle it. From draggingEntered:, you return the contant NSDragOperationNone to indicate that your object won't accept a the drag.

I just followed the discussion in AB&Y's "Cocoa Programming" and adding drag & drop to my image view subclass was a piece of cake. Hillegass' "Cocoa Programming for Mac OS X" has a good chapter on drag and drop, too.

Bill

PS. An alternative approach would be to treat the NSImageView as a button. Since NSImageView inherits from NSControl, it can have an action method designated to it. When you drop an image on an NSImageView instance, an action is fired off, messaging a method that you specify as the NSImageView's target. I believe that by taking this approach, you sacrifice some level of control over the whole drag&drop operation, but your needs might be satisfied just the same. I haven't tried the approach myself, so I can't say from experience.
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 >Delegate methods for NSImageView (?) (From: email@hidden)



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