CALayer position contains NaN: [nan nan] During Drag and Drop

I've seen this pop up a few times. I don't remember what I did to fix it, but I think it had something to do with a bad constraint setup.

Thanks for responding. Don't think that's the case for me. I'm not using autolayout 😮

Hmm. You aren't doing anything funny with your layer backing, are you?

I don't think so. I have a customized IKImageBrowserView subclass, with some custom cells. I draw a few extra things in a cell subclass layer, but I don't do much Core Animation myself in this app.

This seems to happen when I drag the images back and forth from my window to Finder over and over again..it doesn't happen consistently though, hard to reproduce.

Right, but when I experienced this issue, I never had to change any Core Animation code in order to fix it. It had at least something to do with view layout and the layer backing. It might have been a width or height accidentally getting set to 0, but I really don't remember for sure. It wasn't a hard fix, otherwise I'd remember what I had to do! 🙂

I was logging out the frame of the dragging item I set... I didn't hit any 0 frame sizes, but i'll try to look out for that a bit more.

I figured that must have been it too, and somewhere under the covers OS X was using the frame size as a reference and dividing by 0...but I didn't find it yet.

Well, I'll keep trying to remember what I did to fix the issue…

Do let me know if you find anything else that's interesting—I'd love to hear it!

I think I got it. When many items are being dragged at once, I capped the number of visible items to a max amount. Since in the UI, the icons get stacked on top of eachother with a badge showing the amount dragged, I decided to set the imageComponentsProvider to nil on dragging items after the max is exceeded. It seems pointless to create a bunch of images that can't be seen.

The block may be set to nil, meaning that this drag item has no image.

Pretty sure hiding the dragging items this way can cause the issue....I had this before to hide the dragging item...prior to the last update:

[dragItem setDraggingFrame:NSZeroRect contents:nil];

And didn't hit the issue before...but I got an annoying nonnull warning for the contents param...so I changed it...

I capped the number of drag images to 15...and decided to stack them...it seems pretty wasteful to make an image for every item especially when you stack them...I don't know if I should revert the code or pass in blank image as the contents...or just make an image for every since dragging item.

Good work isolating the issue!

Here's an idea: try adding a bit of context-sensitive information into the contents provider to implement the cap, like this:

var timesCalled = 0
var itemCap = 15

dragItem.imageComponentsProvider = {
     timesCalled += 1
     if timesCalled > itemCap {
          //Return an empty image array
          return []
     } else {
          //Process and return the drag images
     }
}

This way, you won't be fooling around with nil and NSZeroRect. Give it a try and let me know how it works! 🙂

Here's what I was doing in update dragging items section in one view...

  __block NSUInteger numberOfDragItems = 0;
   const NSUInteger maxNumberOfDragItems = 15;
    
        [sender enumerateDraggingItemsWithOptions:NSDraggingItemEnumerationClearNonenumeratedImages
                                          forView:self
                                          classes:@[[NSURL class]]
                                    searchOptions:@{NSPasteboardURLReadingFileURLsOnlyKey: @(YES)}
                                       usingBlock:^(NSDraggingItem *draggingItem, NSInteger idx, BOOL *stop)
         {
             if (numberOfDragItems < maxNumberOfDragItems)
             {
                 NSURL *urlForItem = draggingItem.item;
             
                 NSImage *dragImage = doGetDragImageForURL(urlForItem);
             
                 [draggingItem setDraggingFrame:NSMakeRect(0.0,
                                                           0.0,
                                                           dragImage.size.width,
                                                           dragImage.size.height)
                                       contents:dragImage];
             }
             else { NSLog(@"whoops"); }
         
             numberOfDragItems++;

              if (numberOfDragItems >= maxNumberOfDragItems) {  *stop = YES; }
         }];

For the items beyond max...they don't hide though, they stay in there current formation....which isn't what I'm after. I want them to all stack up.

I changed it the code to this based on your previous post:

[sender enumerateDraggingItemsWithOptions:0
                                          forView:self
                                          classes:@[[NSURL class]]
                                    searchOptions:@{NSPasteboardURLReadingFileURLsOnlyKey: @(YES)}
                                       usingBlock:^(NSDraggingItem *draggingItem, NSInteger idx, BOOL *stop)
         {
             if (numberOfDragItems < maxNumberOfDragItems)
             {
                 NSURL *urlForItem = draggingItem.item;
              
                 NSImage *dragImage = doGetDragImageForURL(urlForItem);
              
                 [draggingItem setDraggingFrame:NSMakeRect(0.0,
                                                           0.0,
                                                           dragImage.size.width,
                                                           dragImage.size.height)
                                       contents:dragImage];
             }
             else
             {
                 draggingItem.imageComponentsProvider = ^NSArray<NSDraggingImageComponent *> * _Nonnull
                 {
                     return @[];
                 };
             }
          
             numberOfDragItems++;
         }];

So far, I haven't hit the issue yet... will have to do more testing. Not sure if i'm better off keeping track of the # of times its called in the imageComponentsBlock itself like in your sample.

Shouldn't setting the imageComponentsProvider to nil, or returning an empty array, or setting the contents to nil, all behave the same way?

By, "I haven't hit the issue yet," do you mean that it's not crashing anymore?

Actually I'm still hitting the bug when returning an empty array from the image components provider block..

In my limited testing...I wasn't hitting the crash, but I just hit it. Since it's difficult to reproduce...I still wasn't confident that that fixed it...I did just hit the crash again though...

Here's the only other thing I can think of trying right now. None of this really feels elegant...

On the items I want to 'hide'...

[draggingItem setDraggingFrame:NSMakeRect(0.0, 0.0, 1.0, 1.0) contents:EmtpyDragImage];

EmptyDragImage is just an instance of NSImage...with a size of 1.0, 1.0.

no crashes with a dummy image in there, but sometimes no images show up at all...so I guess the way the system stacks the images is unpredicatable...

Guess I will just return a imageComponentsProvider for all of them and trust that OS X will do a decent job making sure not to make too many images. I wasn't using the block before, I was just setting the images directly...so I'm hoping if I create the image in the block I'll get better performance.

What I can't figure out, is how to position a NSDraggingImageComponent. The coordinate system seems whacky? I tried using the image size and the draggingFrame to calculate the frame for the component, but the images go everywhere. Say I want to position all the drag images center on the mouse location (stacked)...do you know how to calculate it?

  NSRect draggingRect = draggingItem.draggingFrame;

//in the block...

CGFloat x = (draggingRect.size.width/2.0)-(sizeForItem/2.0);
CGFloat y = (draggingRect.size.height/2.0)-(sizeForItem/2.0);

imageComponent.frame = NSMakeRect(x, y , sizeForItem, sizeForItem);