UIView+FFGradient

UIView+FFGradient.h

//
//  UIView+FFGradient.h
//
//  Created by Florian Friedrich on 22.04.14.
//  Copyright (c) 2014 Florian Friedrich. All rights reserved.
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"),
//  to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense,
//  and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
//  WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//


#import <UIKit/UIKit.h>

/**
 *  Represents a stop in an FFGradient.
 *  @see FFGradient
 */
@interface FFGradientStop : NSObject
/**
 *  The color of the stop.
 */
@property (nonatomic, strong) UIColor *color;
/**
 *  Where the color will be. Must be between 0.0f and 1.0f.
 */
@property (nonatomic, strong) NSNumber *location;
/**
 *  Creates a new FFGradientStop with a color and a location.
 *  @param color    The color for the stop.
 *  @param location The location of the stop.
 *  @return A new FFGradientStop instance.
 */
+ (instancetype)stopWithColor:(UIColor *)color location:(CGFloat)location;
/**
 *  Creates a new FFGradientStop with only a color.
 *  @param color The color for the stop.
 *  @return A new FFGradientStop instance.
 */
+ (instancetype)stopWithColor:(UIColor *)color;
/**
 *  Creates a new FFGradientStop with a color and a location.
 *  @param color    The color for the stop.
 *  @param location The location of the stop.
 *  @return A new FFGradientStop instance.
 */
- (instancetype)initWithColor:(UIColor *)color location:(NSNumber *)location;
@end

/**
 *  Represents a gradient.
 */
@interface FFGradient : NSObject
/**
 *  An array of FFGradientStop instances.
 */
@property (nonatomic, strong) NSArray *stops;

/**
 *  Creates a new FFGradient with given stops.
 *  @param stops The stops of the new gradient.
 *  @return A new FFGradient instance.
 */
+ (instancetype)gradientWithStops:(NSArray *)stops;
/**
 *  Creates a new FFGradient with given stops.
 *  @param stops The stops of the new gradient.
 *  @return A new FFGradient instance.
 */
- (instancetype)initWithStops:(NSArray *)stops;

/**
 *  Calculates the locations for the stops for a linear gradient.
 */
- (void)calculateLocations;
@end

/**
 *  Allows to set an FFGradient as UIView background.
 */
@interface UIView (FFGradient)
/**
 *  The view's background gradient.
 */
@property (nonatomic, strong) FFGradient *backgroundGradient;
@end

UIView+FFGradient.m

//
//  UIView+FFGradient.m
//
//  Created by Florian Friedrich on 22.04.14.
//  Copyright (c) 2014 Florian Friedrich. All rights reserved.
//

#import "UIView+FFGradient.h"
#import <objc/runtime.h>
#import <QuartzCore/QuartzCore.h>

@implementation FFGradientStop

+ (instancetype)stopWithColor:(UIColor *)color location:(CGFloat)location
{
    return [[self alloc] initWithColor:color location:@(location)];
}

+ (instancetype)stopWithColor:(UIColor *)color
{
    return [[self alloc] initWithColor:color location:nil];
}

- (instancetype)initWithColor:(UIColor *)color location:(NSNumber *)location
{
    NSAssert(location.floatValue >= 0.0f, @"Location must be between 0.0f and 1.0f!");
    NSAssert(location.floatValue <= 1.0f, @"Location must be between 0.0f and 1.0f!");
    self = [super init];
    if (self) {
        self.color = color;
        self.location = location;
    }
    return self;
}

- (instancetype)init { return [self initWithColor:nil location:nil]; }

@end


NSString *const FFGradientLayerName = @"FFGradientLayer";
@interface FFGradient ()
@property (nonatomic, strong, readonly) CAGradientLayer *gradientLayer;
@end

@implementation FFGradient

+ (instancetype)gradientWithStops:(NSArray *)stops
{
    return [[self alloc] initWithStops:stops];
}

- (instancetype)initWithStops:(NSArray *)stops
{
    self = [super init];
    if (self) {
        self.stops = stops;
    }
    return self;
}

- (instancetype)init { return [self initWithStops:nil]; }

- (void)calculateLocations
{
    CGFloat count = (CGFloat)self.stops.count - 1.0f;
    [self.stops enumerateObjectsUsingBlock:^(FFGradientStop *gStop, NSUInteger idx, BOOL *stop) {
        gStop.location = @((CGFloat)idx / count);
    }];
}

- (CAGradientLayer *)gradientLayer
{
    if (!self.stops.count) return nil;
    
    NSMutableArray *colors = [NSMutableArray array];
    NSMutableArray *locations = [NSMutableArray array];
    CGFloat count = (CGFloat)self.stops.count - 1.0f;
    [self.stops enumerateObjectsUsingBlock:^(FFGradientStop *gStop, NSUInteger idx, BOOL *stop) {
        UIColor *color = gStop.color;
        if (!color) color = [UIColor clearColor];
        [colors addObject:(__bridge id)gStop.color.CGColor];
        NSNumber *location = gStop.location;
        if (!location) location = @((CGFloat)idx / count);
        [locations addObject:location];
    }];
    CAGradientLayer *gradient = [CAGradientLayer layer];
    gradient.colors = [colors copy];
    gradient.locations = [locations copy];
    gradient.name = FFGradientLayerName;
    return gradient;
}

@end


@implementation UIView (FFGradient)
static NSString *const FFBackgroundGradientKey = @"FFBackgroundGradient";

- (FFGradient *)backgroundGradient
{
    return objc_getAssociatedObject(self, (__bridge const void *)(FFBackgroundGradientKey));
}

- (void)setBackgroundGradient:(FFGradient *)backgroundGradient
{
    objc_setAssociatedObject(self, (__bridge const void *)(FFBackgroundGradientKey),
                             backgroundGradient, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    [[self.layer.sublayers copy] enumerateObjectsUsingBlock:^(CALayer *l, NSUInteger idx, BOOL *stop) {
        if ([l.name isEqualToString:FFGradientLayerName]) {
            [l removeFromSuperlayer];
        }
    }];
    if (backgroundGradient) {
        CAGradientLayer *gradientLayer = backgroundGradient.gradientLayer;
        gradientLayer.frame = self.bounds;
        [self.layer insertSublayer:gradientLayer atIndex:0];
    }
}

@end

Example usages

With locations specified:

NSArray *stops = @[
                   [FFGradientStop stopWithColor:[UIColor greenColor] location:0.0f],
                   [FFGradientStop stopWithColor:[UIColor yellowColor] location:0.5f],
                   [FFGradientStop stopWithColor:[UIColor redColor] location:1.0f]
                   ];
self.gradientView.backgroundGradient = [FFGradient gradientWithStops:stops];

Without locations specified:

NSArray *stops = @[
                   [FFGradientStop stopWithColor:[UIColor blueColor]],
                   [FFGradientStop stopWithColor:[UIColor purpleColor]],
                   [FFGradientStop stopWithColor:[UIColor greenColor]],
                   [FFGradientStop stopWithColor:[UIColor yellowColor]],
                   [FFGradientStop stopWithColor:[UIColor orangeColor]],
                   [FFGradientStop stopWithColor:[UIColor redColor]]
                   ];
self.gradientView.backgroundGradient = [FFGradient gradientWithStops:stops];

If you don't specify the locations they will be calculated to become a regular linear gradient when you set it as backgroundGradient of a view. You can also force the calculation (or a re-calculation) yourself by calling [myGradient calculateLocations]; where myGradient is an FFGradient instance.