Drag and Drop into a `UICollectionView` placeholder in iOS 11 Beta 4 - ios

Question

The API for dragging and dropping into a UICollectionView changed in iOS 11 Beta 4. In beta 1-3, the code looked like:
let placeholderContext = coordinator.drop(
item.dragItem,
toPlaceholderInsertedAt: indexPath,
withReuseIdentifier: "reuseID",
cellUpdateHandler: { _ in }
)
In beta 4, the introduced UICollectionViewDropPlaceholder. My code is
let placeholder = UICollectionViewDropPlaceholder(
insertionIndexPath: indexPath,
reuseIdentifier: "reuseID"
)
let placeholderContext = coordinator.drop(item.dragItem, to: placeholder)
I am getting this compile error:
Undefined symbols for architecture arm64:
"_OBJC_CLASS_$_UICollectionViewDropPlaceholder", referenced from:
objc-class-ref in StickerLibraryViewController.o
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
note: symbol(s) not found for architecture arm64
error: linker command failed with exit code 1 (use -v to see invocation)
Other than not using a placeholder until beta 5, anyone have any ideas of how to get this working in beta 4?
Thanks!

Answer 1

Until this is fixed in Beta 5, I ended up solving this issue by dropping down into the Objective-C runtime.
In the Obj-C header…
NS_ASSUME_NONNULL_BEGIN
#interface RKNFactory : NSObject
- (UICollectionViewDropPlaceholder*)placeholderForIndexPath:(NSIndexPath*)indexPath resuseIdentifier:(NSString*)reuseIdentifier;
#end
NS_ASSUME_NONNULL_END
In the implementation…
#import ObjectiveC.runtime;
#implementation RKNFactory
- (UICollectionViewDropPlaceholder*)placeholderForIndexPath:(NSIndexPath*)indexPath resuseIdentifier:(NSString*)reuseIdentifier {
SEL initSelector = NSSelectorFromString(#"initWithInsertionIndexPath:reuseIdentifier:");
Class placeholderClass = NSClassFromString(#"UICollectionViewDropPlaceholder");
return [[placeholderClass alloc] performSelector:initSelector withObject:indexPath withObject:reuseIdentifier];
}
#end
And then from the Swift code…
return RKNFactory().placeholder(for: indexPath, resuseIdentifier: reuseIdentifier)

Answer 2

I had a similar problem with local authentication not compiling on on the simulator architecture when it was in beta.
Does it compile if you remove arm64 from valid architectures in build settings (or turn off “build all architectures”)?
If they compiled this symbol for simulator, but left it out for arm64, the only solution might be to prevent it from compiling on arm64 and test it only on the simulator for now.
You can also wrap the code temporarily in a “#if block” that prevents the compiler from looking at it when building arm64.
Finally, if you’re building for any versions of iOS under iOS 11, be sure to try turning those off for now, in case they forgot to mark API availability (which might have let the compiler provide a more helpful message).