Ask NSSlider if the user still has the mouse button pressed? (swift)

Question

Hi I'm implementing a subclass of NSSlider and NSSliderCell in swift, I would like to check/retrieve the _scFlags.isPressed property from NSSliderCell, I found that there is a 'hack' in Objective-C to do it when calling from another class (which is not really needed if you subclass NSSlider in Objective-C):

http://www.cocoabuilder.com/archive/cocoa/54913-nsslider.html

However, in swift, when I search in the API (AppKit -> NSSliderCell), I can find a struct which I suppose is the one I need, and nothing else but the init() inside:

public struct __sliderCellFlags {
    public init()
}

and I can't even call it from the subclass. All these show as error:

self.__sliderCellFlags 
self._scFlags
super.__sliderCellFlags
super._scFlags

Am I missing something? Is there a different way to call these properties?

Answer 1

Use Objective-C to implement a category on NSSliderCell which has a property to access the struct data and use the property from Swift.

NSSlider+FlagsAccessor.h

@interface NSSlider (FlagsAccessor)

@property (nonatomic, readonly) BOOL isPressed;

@end

NSSlider+FlagsAccessor.m

#import "NSSlider+FlagsAccessor.h"

@interface NSSliderCell (FlagsAccessor)

@property (nonatomic, readonly) BOOL isPressed;

@end

@implementation NSSlider (FlagsAccessor)

- (BOOL)isPressed
{
    NSSliderCell *cell = self.cell;

    return cell.isPressed;
}

@end

@implementation NSSliderCell (FlagsAccessor)

- (BOOL)isPressed
{
    return self->_scFlags.isPressed == 1;
}

@end

Then to use It from Swift just call self.isPressed. Here's a sample project.

Don't forget to import your category header in your bridging header (Xcode will prompt you to create a bridging header when you add Objective-C code to a Swift project).