Making NSArray IBInspectable

Is there a way to use NSArray IBInspectable in order to define multiple values in Storyboard custom view?

I know that NSArray doesn't have any information about the type of object that will be stored in it so it probably is a problem. But there is some solution using annotation or something?

What I want to do is set an NSArray of UIColors via Storyboard and draw a Gradient Layer in the view during Storyboard visualization.

I started creating two properties called startColor and endColor. That works fine but I want to do this more generic.

This is my drawRect method:

- (void)drawRect:(CGRect)rect {
    CAGradientLayer *gradientLayer = [CAGradientLayer layer];
    
    gradientLayer.frame = self.bounds;
    
    gradientLayer.colors = [NSArray arrayWithObjects:(id)[self.startColor CGColor], (id)[self.endColor CGColor], nil];
    
    [self.layer addSublayer:gradientLayer];
}

And I want to do something like this:

- (void)drawRect:(CGRect)rect {
    CAGradientLayer *gradientLayer = [CAGradientLayer layer];
    
    gradientLayer.frame = self.bounds;
    
    // colorsArray should be an IBInspectable property in order to be setted on Storyboard Attributes Inspector
    gradientLayer.colors = self.colorsArray;
    
    [self.layer addSublayer:gradientLayer];
}

Xcode doesn't support inspectable arrays as of version 7.1.

You can cheese it for a gradient layer if you pick a maximum number of gradient stops. Here's what my test looks like, where I hardcoded six stops:

Incidentally, you shouldn't add subviews or sublayers in drawRect:. The system doesn't expect updates to the layer hierarchy at that stage. You should do it in layoutSubviews.

Here's the code I used to create that screen shot.

GradientView.h

#import <UIKit/UIKit.h>

IB_DESIGNABLE
@interface GradientView : UIView

@property(nonatomic, readonly, strong) CAGradientLayer *layer;

@property (nonatomic) IBInspectable CGPoint startPoint;
@property (nonatomic) IBInspectable CGPoint endPoint;

@property (nonatomic, strong) IBInspectable UIColor *color0;
@property (nonatomic) IBInspectable CGFloat location0;

@property (nonatomic, strong) IBInspectable UIColor *color1;
@property (nonatomic) IBInspectable CGFloat location1;

@property (nonatomic, strong) IBInspectable UIColor *color2;
@property (nonatomic) IBInspectable CGFloat location2;

@property (nonatomic, strong) IBInspectable UIColor *color3;
@property (nonatomic) IBInspectable CGFloat location3;

@property (nonatomic, strong) IBInspectable UIColor *color4;
@property (nonatomic) IBInspectable CGFloat location4;

@property (nonatomic, strong) IBInspectable UIColor *color5;
@property (nonatomic) IBInspectable CGFloat location5;

@end

GradientView.m

#import "GradientView.h"

#define MaxStops 6

typedef struct {
    CGColorRef color;
    CGFloat location;
} GradientStop;

@implementation GradientView

@dynamic layer;

- (void)setStartPoint:(CGPoint)startPoint {
    self.layer.startPoint = startPoint;
}

- (CGPoint)startPoint {
    return self.layer.startPoint;
}

- (void)setEndPoint:(CGPoint)endPoint {
    self.layer.endPoint = endPoint;
}

- (CGPoint)endPoint {
    return self.layer.endPoint;
}

#define DefineSetters(i) \
    - (void)setColor##i:(UIColor *)color##i { \
        _color##i = color##i; \
        [self setNeedsLayout]; \
    } \
 \
    - (void)setLocation##i:(CGFloat)location##i { \
        _location##i = location##i; \
        [self setNeedsLayout]; \
    }

DefineSetters(0)
DefineSetters(1)
DefineSetters(2)
DefineSetters(3)
DefineSetters(4)
DefineSetters(5)

+ (Class)layerClass {
    return [CAGradientLayer class];
}

- (void)layoutSubviews {
    [super layoutSubviews];
    [self updateGradient];
}

static BOOL isValidStop(const GradientStop *stop) {
    return stop->color != nil && stop->location >= 0 && stop->location <= 1;
}

static int compareStops(const void *a, const void *b) {
    const GradientStop *stop0 = a;
    const GradientStop *stop1 = b;

    if (isValidStop(stop0) && isValidStop(stop1)) {
        if (stop0->location < stop1->location) {
            return -1;
        } else if (stop0->location > stop1->location) {
            return 1;
        } else {
            return 0;
        }
    } else if (isValidStop(stop0)) {
        return -1;
    } else if (isValidStop(stop1)) {
        return 1;
    } else {
        return 0;
    }
}

static size_t countOfValidStops(const GradientStop *stops, size_t maxStops) {
    for (size_t i = 0; i < maxStops; ++i) {
        if (!isValidStop(&stops[i])) {
            return i;
        }
    }
    return maxStops;
}

- (void)updateGradient {
    GradientStop stops[MaxStops];
    [self setStop:stops+0 color:self.color0 location:self.location0];
    [self setStop:stops+1 color:self.color1 location:self.location1];
    [self setStop:stops+2 color:self.color2 location:self.location2];
    [self setStop:stops+3 color:self.color3 location:self.location3];
    [self setStop:stops+4 color:self.color4 location:self.location4];
    [self setStop:stops+5 color:self.color5 location:self.location5];
    qsort(stops, MaxStops, sizeof *stops, compareStops);

    size_t count = countOfValidStops(stops, MaxStops);
    NSMutableArray *colors = [NSMutableArray arrayWithCapacity:count];
    NSMutableArray *locations = [NSMutableArray arrayWithCapacity:count];
    [self populateColors:colors locations:locations fromStops:stops count:count];
    self.layer.colors = colors;
    self.layer.locations = locations;
}

- (void)setStop:(GradientStop *)stop color:(UIColor *)color location:(CGFloat)location {
    stop->color = color.CGColor;
    stop->location = location;
}

- (void)populateColors:(NSMutableArray *)colors locations:(NSMutableArray *)locations fromStops:(const GradientStop *)stops count:(size_t)count {
    for (size_t i = 0; i < count; ++i) {
        [colors addObject:(__bridge id)stops[i].color];
        [locations addObject:@(stops[i].location)];
    }
}

@end

GradientView.h

GradientView.m

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