Runtime精简iOS App的UIButton使用多张图片显

因为需求提出需要，UI要有两种模式。

这就需要美工为每个按钮提供4张图，即：模式A按钮normal状态、按钮display状态，模式B按钮normal状态、按钮display状态。

1. 为UIButton添加两个属性tintNormalColor和tintDisabledColor，分别用于Normal和Disabled情况下的使用。根据实际情况，也可以添加Select等等

@interface UIButton (YourName)
@property(nonatomic,strong) UIColor *tintNormalColor;
@property(nonatomic,strong) UIColor *tintDisabledColor;
@end

2. 使用objc_getAssociatedObject和objc_getAssociatedObject为分类增加属性。
   再重写SetEnabled的方法，使UIButton在工作的时候可以自动调用刚刚添加的两个属性。

#import "UIButton+YourName.h"
static const char TintNormalColor_KEY;
static const char TintDisabledColor_KEY;

@implementation UIButton (YourName)

+ (void)load
{
    Method systemMethod = class_getInstanceMethod([UIButton class], @selector(setEnabled:));
    
    Method myMethod = class_getInstanceMethod([UIButton class], @selector(WS_SetEnabled:));
    
    //2.进行方法的交换
    method_exchangeImplementations(systemMethod, myMethod);
}

- (void)WS_SetEnabled:(BOOL)enabled
{
    if (enabled) {
        self.tintColor = self.tintNormalColor;
    }else{
        self.tintColor = self.tintDisabledColor;
    }
    [self WS_SetEnabled:enabled];
}

- (void)setTintNormalColor:(UIColor *)tintNormalColor
{
    if (self.isEnabled) {
        self.tintColor = tintNormalColor;
    }
    objc_setAssociatedObject(self, &TintNormalColor_KEY, tintNormalColor, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
- (UIColor*)tintNormalColor
{
    return objc_getAssociatedObject(self, &TintNormalColor_KEY);
}
- (void)setTintDisabledColor:(UIColor *)tintDisabledColor
{
    if (!self.isEnabled) {
        self.tintColor = tintDisabledColor;
    }
    objc_setAssociatedObject(self, &TintDisabledColor_KEY, tintDisabledColor, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
- (UIColor*)tintDisabledColor
{
    return objc_getAssociatedObject(self, &TintDisabledColor_KEY);
}

@end