Modernising dragging problem
Modernising dragging problem
- Subject: Modernising dragging problem
- From: Graham Cox <email@hidden>
- Date: Sat, 31 Jan 2015 10:15:26 +1100
I'm updating some older code that uses the now-deprecated [NSView dragImage:at:offset:pasteboard:source:slideback:] to use NSDraggingSession and pals. Note that this older code works just fine, I've never had any issues with it. I'm doing this mostly just to clear out compiler warnings, though my instinct tells me not to "fix" code that isn't broken.
Sadly its replacement is broken.
In order to use NSDraggingItem, I first need to make sure the stuff I'm dragging supports NSPasteboardWriting. I've done that, it seems straightforward enough. Then I build a NSDraggingItem and use the same image I previously used, so there's nothing new there. Finally I use [NSView beginDraggingSessionWithItems:event:source:].
Nothing shows up. No image, nothing drags. I can break on the NSPasteboardWriting methods and see that they are being called, so it seems to be trying to write the correct things to the pasteboard. Nothing is logged. After this, use of the legacy dragging methods elsewhere in the app also fail to work - it's like whatever I did in this drag session messes up the dragging system altogether. Obviously I'm doing something wrong, but I've been over the docs and am just not getting it.
One thing is that the docs state that this new dragging method returns immediately and the drag itself is somehow magically handled on the next turn of the event loop. I think the older approach kept control for the duration of the drag. That seems like a very different situation from the app's point of view, and makes updating legacy code that expects it to keep control quite difficult. That might be where things are messing up, so I'll look into that... unless anyone can spot an obvious problem otherwise. Or would it just be better to stick with working code and ignore the deprecation warnings? Those warnings really go against the grain of everything I've ever learned about coding which is "if it ain't broke don't fix it".
Here's the code:
- (void) dragStyleOrSymbol:(id<DKOLibraryObjectProtocol>) obj event:(NSEvent*) event source:(id) sourceObject slideBack:(BOOL) slideBack
{
NSAssert( obj != nil, @"can't drag a nil style or symbol");
// can pass in nil to mean self
if( sourceObject == nil )
sourceObject = self;
// create the drag image
NSImage* dragImage = [obj image];
NSPoint mdLoc = [self convertPoint:[event locationInWindow] fromView:nil];
mdLoc.x -= [dragImage size].width * 0.5;
mdLoc.y -= [dragImage size].height * 0.5;
#if (LEGACY_ CODE)
NSPasteboard* dragPBoard = [NSPasteboard pasteboardWithName:NSDragPboard];
// put the object on the pasteboard
[obj copyToPasteboard:dragPBoard];
// start dragging it
[self dragImage:dragImage at:mdLoc offset:NSZeroSize event:event pasteboard:dragPBoard source:sourceObject slideBack:slideBack];
#else
NSDraggingItem* dragItem = [[[NSDraggingItem alloc] initWithPasteboardWriter:obj] autorelease];
NSRect dragFrame;
dragFrame.origin = mdLoc;
dragFrame.size = dragImage.size;
[dragItem setDraggingFrame:dragFrame contents:dragImage];
NSDraggingSession* session = [self beginDraggingSessionWithItems:@[dragItem] event:event source:sourceObject];
session.animatesToStartingPositionsOnCancelOrFail = slideBack;
#endif
}
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