Question

I’m looking for an explanation of NSWindow’s dragImage method.

- (void)dragImage:(NSImage *)image at:(NSPoint)imageLocation offset:(NSSize)pointerOffset event:(NSEvent *)event pasteboard:(NSPasteboard *)pasteboard source:(id)sourceObject slideBack:(BOOL)slideBack

Any help?

Answer 1

The NSView documentation of that method provides a much more detailed explanation, including example code. The only difference between the two methods is the coordinate system that imageLocation is in. Find it at http://developer.apple.com/library/mac/documentation/Cocoa/Reference/ApplicationKit/Classes/NSView_Class/Reference/NSView.html#//apple_ref/doc/uid/20000014-SW135

Edit: Here is the sample code from that link, with added comments.

- (void)mouseDown:(NSEvent *)theEvent {
    // Create an offset for the offset parameter. Since it is ignored, you should just use 0,0.
    NSSize dragOffset = NSMakeSize(0.0, 0.0);
    NSPasteboard *pboard;

    // Get the pasteboard used to hold drag-and-drop data
    pboard = [NSPasteboard pasteboardWithName:NSDragPboard];
    // Declare the data type used on the pasteboard. This sample passes a TIFF representation of an image
    [pboard declareTypes:[NSArray arrayWithObject:NSTIFFPboardType]  owner:self];
    // Add the data to the pasteboard.
    [pboard setData:[[self image] TIFFRepresentation] forType:NSTIFFPboardType];
    // Call dragImage:... with:
    // An image representing the object you are dragging. This could be a file's icon or a screenshot of a view, etc.
    [self dragImage:[self image]
    // The starting location of the image in this views coordinates. This should be close to the location of the object you are dragging.
                 at:[self imageLocation]
    // An NSSize structure. This is not used.
             offset:dragOffset
    // The mousedown event
              event:theEvent
    // The pasteboard which contains the data
         pasteboard:pboard
    // The object providing the data
             source:self
    // Whether or not the image should slide to its starting location if the drag isn't completed.
          slideBack:YES];

}

The source object (self in this case) needs to implement the NSDraggingSource protocol. You may also be interested in the NSPasteboard Class Reference.