NSTextField enabled for drag and drop from finder

DragAndDropTextField.h

#import <Cocoa/Cocoa.h>

@interface DragAndDropTextField : NSTextField

@end

DragAndDropTextField.mm

#import "DragAndDropTextField.h"


@interface DragAndDropTextField ()
@property (nonatomic) bool dragIsOver;
@end

@implementation DragAndDropTextField

- (void) awakeFromNib {
    [self registerForDraggedTypes:[NSArray arrayWithObjects: NSFilenamesPboardType, nil]];
}

- (void)drawRect:(NSRect)dirtyRect {
    
    [NSGraphicsContext saveGraphicsState];
    [super drawRect:dirtyRect];
    if (_dragIsOver)
    {
        [[[NSColor keyboardFocusIndicatorColor] colorWithAlphaComponent:0.25] set];
        NSRectFill(NSInsetRect(self.bounds, 1, 1));
    }
    [NSGraphicsContext restoreGraphicsState];

}

- (NSDragOperation)draggingEntered:(id <NSDraggingInfo>)sender {
    if ( [[[sender draggingPasteboard] types] containsObject:NSFilenamesPboardType] ) {
        _dragIsOver = true;
        [self setNeedsDisplay];
        return NSDragOperationCopy;
    }
    return NSDragOperationNone;
}

- (void)draggingExited:(nullable id <NSDraggingInfo>)sender {
    _dragIsOver = false;
    [self setNeedsDisplay];
}

- (BOOL)performDragOperation:(id <NSDraggingInfo>)sender {
    NSPasteboard *pboard = [sender draggingPasteboard];
    if ( [[pboard types] containsObject:NSFilenamesPboardType] ) {
        NSArray *files = [pboard propertyListForType:NSFilenamesPboardType];
        NSString *url = [files objectAtIndex:0];
        if (url)
        {
            self.stringValue = url;
            _dragIsOver = false;
            [self setNeedsDisplay];
        }
    }
    return YES;
}

@end