Color Swatch view for Mac Catalyst that implements inter-app drag & drop

PSTLDraggableColorSwatchView.h

//
//  PSTLDraggableColorSwatchView.h
//  Pastel
//
//  Created by Steven Troughton-Smith on 06/03/2020.
//  Copyright © 2020 Steven Troughton-Smith. All rights reserved.
//

@import UIKit;

NS_ASSUME_NONNULL_BEGIN

@interface PSTLDraggableColorSwatchView : UIView <UIDragInteractionDelegate, UIDropInteractionDelegate>

@property (nonatomic) UIColor *color;

@end

NS_ASSUME_NONNULL_END

PSTLDraggableColorSwatchView.m

//
//  PSTLDraggableColorSwatchView.m
//  Pastel
//
//  Created by Steven Troughton-Smith on 06/03/2020.
//  Copyright © 2020 Steven Troughton-Smith. All rights reserved.
//

#import "PSTLDraggableColorSwatchView.h"

@import ObjectiveC.runtime;

@implementation NSObject (UINS)

-(NSUInteger)PSTLdraggingSession:(void *)arg2 sourceOperationMaskForDraggingContext:(long long)arg3
{
	return 0xff;
}
@end

@implementation PSTLDraggableColorSwatchView

+(void)load
{
	{
		Method m1 = class_getInstanceMethod(NSClassFromString(@"UINSDragManager"), NSSelectorFromString(@"draggingSession:sourceOperationMaskForDraggingContext:"));
		Method m2 = class_getInstanceMethod(NSClassFromString(@"UINSDragManager"), @selector(PSTLdraggingSession:sourceOperationMaskForDraggingContext:));
		method_exchangeImplementations(m1, m2);
	}
}

- (instancetype)initWithFrame:(CGRect)frame
{
	self = [super initWithFrame:frame];
	if (self) {
		UIDragInteraction *dragInteraction = [[UIDragInteraction alloc] initWithDelegate:self];
		dragInteraction.enabled = YES;
		[self addInteraction:dragInteraction];
		
		UIDropInteraction *dropInteraction = [[UIDropInteraction alloc] initWithDelegate:self];
		[self addInteraction:dropInteraction];
	}
	return self;
}

- (void)setColor:(UIColor *)color
{
	_color = color;
	self.backgroundColor = color;
}

#pragma mark - Drag & Drop

- (NSArray<UIDragItem *> *)dragInteraction:(UIDragInteraction *)interaction itemsForBeginningSession:(id<UIDragSession>)session
{
	NSItemProvider *provider = [[NSItemProvider alloc] initWithObject:self.color];
	
	[provider registerDataRepresentationForTypeIdentifier:@"com.apple.cocoa.pasteboard.color" visibility:NSItemProviderRepresentationVisibilityAll loadHandler:^NSProgress * _Nullable(void (^ _Nonnull completionHandler)(NSData * _Nullable, NSError * _Nullable)) {
		
		NSData *d = [NSKeyedArchiver archivedDataWithRootObject:self.color requiringSecureCoding:NO error:nil];
		completionHandler(d, nil);
		
		return nil;
	}];
	
	
	UIDragItem *dragItem = [[UIDragItem alloc] initWithItemProvider:provider];
	
	return @[dragItem];
}

- (BOOL)dropInteraction:(UIDropInteraction *)interaction canHandleSession:(id<UIDropSession>)session
{
	NSItemProvider *item = [[[session items] firstObject] itemProvider];
	BOOL shouldHandle = NO;
	
	for (NSString *type in [item registeredTypeIdentifiers])
	{
		if ([type isEqualToString:@"com.apple.cocoa.pasteboard.color"] || [type isEqualToString:@"com.apple.uikit.color"])
		{
			shouldHandle = YES;
		}
	}
	
	return shouldHandle;
}

- (UIDropProposal *)dropInteraction:(UIDropInteraction *)interaction sessionDidUpdate:(id<UIDropSession>)session
{
	/*
	 NSColorPanel's main swatch drag session is designated as 'local-only', which prevents inter-app drag and drop. Whyyy
	 
	 We can override that by poking at some private properties…
	 */
	
	@try {
		[(NSObject *)session setValue:@(1) forKeyPath:@"_sessionDestination._outsideAppSourceOperationMask"];
	} @catch (NSException *exception) {
	}
	
	UIDropProposal *proposal = [[UIDropProposal alloc] initWithDropOperation:UIDropOperationCopy];
	proposal.precise = YES;
	
	return proposal;
}

- (void)dropInteraction:(UIDropInteraction *)interaction performDrop:(id<UIDropSession>)session
{
	UIDragItem *item = session.items.firstObject;
	
	NSItemProvider *p = item.itemProvider;
	
	if ([p canLoadObjectOfClass:[UIColor class]])
	{
		[p loadObjectOfClass:[UIColor class] completionHandler:^(UIColor <NSItemProviderReading>*  _Nullable object, NSError * _Nullable error) {
			dispatch_async(dispatch_get_main_queue(), ^{
				
				UIColor *oldColor = self.color;
				
				[[self undoManager] registerUndoWithTarget:self handler:^(id  _Nonnull target) {
					self.color = oldColor;
				}];
				
				self.color = object;
			});
		}];
	}
	else
	{
		[p loadDataRepresentationForTypeIdentifier:@"com.apple.cocoa.pasteboard.color" completionHandler:^(NSData * _Nullable data, NSError * _Nullable error) {
			
			id cc = [NSKeyedUnarchiver unarchivedObjectOfClass:NSClassFromString(@"UIColor") fromData:data error:nil];
			
			dispatch_async(dispatch_get_main_queue(), ^{
				
				UIColor *oldColor = self.color;
				
				[[self undoManager] registerUndoWithTarget:self handler:^(id  _Nonnull target) {
					self.color = oldColor;
				}];
				self.color = (UIColor *)cc;
			});
			
		}];
	}
}

@end