DragDropImageView for Mac OS.

DragDropImageView.m

//
//  DragDropImageView.h
//  TFVideo
//
//  Created by user on 2/1/18.
//  Copyright © 2018 AlexO. All rights reserved.
//

#import <AppKit/AppKit.h>

@protocol DragDropImageViewDelegate
- (void)didDragImage:(NSImage*)image;
@end

@interface DragDropImageView : NSImageView
@property(weak, nonatomic) id<DragDropImageViewDelegate> dragDelegate;
@end

// DragDropImageView.m
#import "DragDropImageView.h"


@interface DragDropImageView ()
@property(nonatomic, assign) BOOL isReceivingDrag;
@end

@implementation DragDropImageView

- (void)awakeFromNib {
    [super awakeFromNib];
    [self registerForDraggedTypes:@[NSFilenamesPboardType, NSStringPboardType, NSURLPboardType]];
    
}

- (void)drawRect:(NSRect)dirtyRect {
    [super drawRect:dirtyRect];
    if (self.isReceivingDrag) {
        NSBezierPath *path = [NSBezierPath bezierPathWithRect:self.bounds];
        path.lineWidth = 4;
        [[NSColor blueColor] set];
        [path stroke];
    }
}

- (void)setIsReceivingDrag:(BOOL)isReceivingDrag {
    _isReceivingDrag = isReceivingDrag;
    self.needsDisplay = YES;
}

- (BOOL)shouldAllowDrag:(id<NSDraggingInfo>)info {
    BOOL canAccept = NO;
    NSPasteboard *p = [info draggingPasteboard];
    if ([p canReadObjectForClasses:@[NSURL.class] options:@{NSPasteboardURLReadingContentsConformToTypesKey : [NSImage imageTypes]}]) {
        canAccept = YES;
    } else {
        
    }
    return canAccept;
}

- (void)draggingExited:(id<NSDraggingInfo>)sender {
    self.isReceivingDrag = NO;
}

- (NSDragOperation)draggingEntered:(id<NSDraggingInfo>)sender {
    BOOL allow = [self shouldAllowDrag:sender];
    self.isReceivingDrag = allow;
    return allow ? NSDragOperationCopy : NSDragOperationNone;
}

- (BOOL)prepareForDragOperation:(id<NSDraggingInfo>)sender {
    self.isReceivingDrag = NO;
    NSPasteboard *p = [sender draggingPasteboard];

    if (!p) return NO;
    
    NSArray *urls = [p readObjectsForClasses:@[NSURL.class] options:@{NSPasteboardURLReadingContentsConformToTypesKey : [NSImage imageTypes]}];
    if (urls && urls.count > 0 && [urls.firstObject isKindOfClass:NSURL.class]) {
        NSImage *image = [[NSImage alloc]initWithContentsOfURL:urls.firstObject];
        if (image) [self.dragDelegate didDragImage: image];
        return YES;
    }
    NSImage *result = [[NSImage alloc]initWithPasteboard:p];
    if (result) {
        [self.dragDelegate didDragImage: result];
        return YES;
    }
    return NO;
}

@end