UIButton背景色

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有一个需求，相信业务需求中总会碰到的吧。按钮点击前背景色是这样的，点击后背景色又是这样的。那么有什么好的方法实现呢？

UIButton 的多个方法可以设置不同 controlState 下的 UI 状态，比如 setTitlecolor，setTitle 等。而 backgroundColor 却没有对应的方法可以进行设置，大多时候是通过 setBackgroundImage: 来设置不同状态下的“背景颜色”。UIView -> UIControl -> UIButton，继承链是这样的。而 backgroundColor 是 UIView 的一个属性。着实无法通过 backgroundColor 来直接设置不同状态下的背景色。兴许 UIKit 的开发工程师也是考虑到了这点，才选择了通过 setBackgroudImage:forState 来设置 UIButton 的不同背景色吧。

其实可以通过 Category 来进行方法扩展。一种是直接生成 不同状态下 backgroundColor 的图片，然后用 setBackgroudImage:forState 来设置，一种是直接记录不同状态下 backgroundColor，直接进行 setBackgroundColor 。

方法一

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static NSString * const kColorForNormal = @"UIControlStateNormal";
static NSString * const kColorForHighlighted = @"UIControlStateHighlighted";
static NSString * const kColorForDisabled = @"UIControlStateDisabled";
static NSString * const kColorForSelected = @"UIControlStateSelected";
static NSString * const kColorForFocused = @"UIControlStateFocused";
static NSString * const kColorForApplication = @"UIControlStateApplication";
static NSString * const kColorForReserved = @"UIControlStateReserved";
@interface UIButton()
@property (nonatomic, strong) NSMutableDictionary *bgColorDict;
@end
@implementation UIButton (ACKit)
- (NSMutableDictionary *)bgColorDict {
    
    return objc_getAssociatedObject(self, _cmd);
}
- (void)setBgColorDict:(NSMutableDictionary *)bgColorDict {
    objc_setAssociatedObject(self, @selector(bgColorDict), bgColorDict, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
- (void)ac_setBackgroundColor:(UIColor *)backgroundColor forState:(UIControlState)state {
    
    if (!backgroundColor) return;
    
    if (!self.bgColorDict) self.bgColorDict = [NSMutableDictionary dictionary];
    
    NSString *key = [self fetchBgColorKey:state];
    self.bgColorDict[key] = backgroundColor;
    
    UIImage *bgImgColor = [self imageWithColor:backgroundColor];
    
    [self setBackgroundImage:bgImgColor forState:state];
    
}
- (UIColor *)ac_backgroundColorForState:(UIControlState)state {
    NSString *key = [self fetchBgColorKey:state];
    return self.bgColorDict[key];
}
- (UIImage *)imageWithColor:(UIColor *)color {
    
    CGRect rect = CGRectMake(0.0f, 0.0f, 1.0f, 1.0f);
    UIGraphicsBeginImageContext(rect.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    
    CGContextSetFillColorWithColor(context, [color CGColor]);
    CGContextFillRect(context, rect);
    
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    return image;
}
@end

这是通过生成一张对应背景色图片从而间接设置背景图片来实现的。为了参考系统方法的，因此还是增多了一个 NSDictionary 来继续不同状态下的 backgroundColor，从而可以 ac_backgroundColorForState: 来得到对应的背景色。其实有点多余呐。（逃

方法二

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static NSString * const kColorForNormal = @"UIControlStateNormal";
static NSString * const kColorForHighlighted = @"UIControlStateHighlighted";
static NSString * const kColorForDisabled = @"UIControlStateDisabled";
static NSString * const kColorForSelected = @"UIControlStateSelected";
static NSString * const kColorForFocused = @"UIControlStateFocused";
static NSString * const kColorForApplication = @"UIControlStateApplication";
static NSString * const kColorForReserved = @"UIControlStateReserved";
@interface UIButton()
@property (nonatomic, strong) NSMutableDictionary *bgColorDict;
@end
@implementation UIButton (ACKit)
+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class class = [self class];
        
        [self swizzleClass:class originalSelector:@selector(setSelected:) swizzledSelector:@selector(ac_setSelected:)];
        [self swizzleClass:class originalSelector:@selector(setHighlighted:) swizzledSelector:@selector(ac_setHighlighted:)];
        [self swizzleClass:class originalSelector:@selector(setEnabled:) swizzledSelector:@selector(ac_setEnabled:)];
        
    });
}
+ (void)swizzleClass:(Class)class originalSelector:(SEL)originalSelector swizzledSelector:(SEL)swizzledSelector {
    
    Method originalMethod = class_getInstanceMethod(class, originalSelector);
    Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
    
    BOOL success = class_addMethod(class, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
    if (success) {
        class_replaceMethod(class, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
    } else {
        method_exchangeImplementations(originalMethod, swizzledMethod);
    }
}
- (void)ac_setBackgroundColor:(UIColor *)backgroundColor forState:(UIControlState)state {
    
    if (!backgroundColor) return;
    
    if (!self.bgColorDict) self.bgColorDict = [NSMutableDictionary dictionary];
    
    NSString *key = [self fetchBgColorKey:state];
    self.bgColorDict[key] = backgroundColor;
    
    if (state == UIControlStateNormal) {
        self.backgroundColor = backgroundColor;
    }
}
- (UIColor *)ac_backgroundColorForState:(UIControlState)state {
    NSString *key = [self fetchBgColorKey:state];
    return self.bgColorDict[key];
}
- (void)ac_setSelected:(BOOL)selected {
    [self ac_setSelected:selected];
    NSString *key = [self fetchBgColorKey:(YES == selected ? UIControlStateSelected : UIControlStateNormal)];
    UIColor *bgColor = self.bgColorDict[key];
    if (bgColor) [self setBackgroundColor:bgColor];
}
- (void)ac_setHighlighted:(BOOL)highlighted {
    [self ac_setHighlighted:highlighted];
    
    if (highlighted) {
        NSString *key = [self fetchBgColorKey: UIControlStateHighlighted];
        UIColor *bgColor = self.bgColorDict[key];
        if (bgColor) [self setBackgroundColor:bgColor];
    } else {
        if (!self.isSelected) {
            NSString *key = [self fetchBgColorKey: UIControlStateNormal];
            UIColor *bgColor = self.bgColorDict[key];
            if (bgColor) [self setBackgroundColor:bgColor];
        }
    }
}
- (void)ac_setEnabled:(BOOL)enabled {
    [self ac_setEnabled:enabled];
    NSString *key = [self fetchBgColorKey:(NO == enabled ? UIControlStateDisabled : UIControlStateNormal)];
    UIColor *bgColor = self.bgColorDict[key];
    if (bgColor) [self setBackgroundColor:bgColor];
    
}
- (NSMutableDictionary *)bgColorDict {
    
    return objc_getAssociatedObject(self, _cmd);
}
- (void)setBgColorDict:(NSMutableDictionary *)bgColorDict {
    objc_setAssociatedObject(self, @selector(bgColorDict), bgColorDict, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
- (NSString *)fetchBgColorKey:(UIControlState)state {
    NSString *key = kColorForNormal;
    switch (state) {
        case UIControlStateNormal:
            key = kColorForNormal;
            break;
        case UIControlStateHighlighted:
            key = kColorForHighlighted;
            break;
        case UIControlStateDisabled:
            key = kColorForDisabled;
            break;
        case UIControlStateSelected:
            key = kColorForSelected;
            break;
        case UIControlStateFocused:
            key = kColorForFocused;
            break;
        case UIControlStateReserved:
            key = kColorForReserved;
            break;
        case UIControlStateApplication:
            key = kColorForApplication;
            break;
        default:
            break;
    }
    return key;
}
@end

这是通过记录不同状态下的 backgroundColor ，再去用 swizzle 去替换掉原先 setSelected: / setEnabled: / setHighlighted: 方法，从而得到实现。但是因为直接判定得到三种状态（ UIControlStateSelected / UIControlStateDisabled / UIControlStateHighlighted )。因此只能实现这三种状态下的切换。

又由于如果是在按钮点击事件中改变 selected 状态，因此在 ac_setHighlighted 方法进行加以判断，这是因为在测试过程中，发现 selected 后还会再次 highlighted。

结尾

觉得在开发过程中，一些好的方法还是设置抽离出来的。比如方法一中的通过颜色得到一个 UIImage。这样的方法其实也可以以扩展方法的形式存在 UIImage 中。再者 Swizzle 的方法其实也可以进行一个抽离。

最后，再上个源码吧。ACKit/ UIButton+ACKit