1、方案1

1.1、架构

方案1.png

1.2、实现

（1）设计一套皮肤文件配置协议

（2）扩展基类（NSObject + Theme），缓存对象和方法

// NSObject + Theme
- (NSMutableArray<ActionBloc> *)action {
    NSMutableArray<ActionBloc> *action = objc_getAssociatedObject(self, @selector(action));
    if (!action) {
        // 不存在，则创建关联
        action = [[NSMutableArray alloc] init];
        objc_setAssociatedObject(self, @selector(action), action, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
    return action;
}

// UIButton + Theme
- (void)them_setImageName:(NSString *)name forState:(UIControlState)state {
    SetImage tmpBlock = ^(){
        UIImage *image = [[ThemEngine sharedInstance] imageForThemeId:name];
        [self setImage:image forState:state];
    };
    
    // 执行
    tmpBlock();
    
    // 缓存方法
    [self.action addObject:[tmpBlock copy]];
}

（3）应用层初始化UI组件，例如UIButton

UIButton *firstBtn = [[UIButton alloc]initWithFrame:CGRectMake(100, 100, 120, 75)];
[firstBtn them_setImageName:@"normalImage" forState:UIControlStateNormal];
[[ThemEngine sharedInstance].themUI addObject:firstBtn]; // 缓存对象
[self.view addSubview:firstBtn];

（4）遍历缓存对象和方法，实现换肤

- (void)changeThem {
    for (int i = 0; i< self.themUI.count; i++) {
        NSObject *obj = (NSObject *)[self.themUI objectAtIndex:i];
        [obj.action enumerateObjectsUsingBlock:^(ActionBloc block, NSUInteger idx, BOOL *stop) {
            block();
        }];
    }   
}

2、方案2

2.1、架构

方案2.png

2.2、实现

（1）设计一套皮肤文件配置协议

（2）扩展基类（NSObject+Theme），缓存方法名和参数

- (void)cacheParams:(NSArray *)params forSelector:(SEL)sel
{
    NSMutableDictionary *cachedParams = [self.cachedMethods objectForKey:NSStringFromSelector(sel)];
    
    if (!cachedParams)
    {
        cachedParams = [[NSMutableDictionary alloc] init];
        [self.cachedMethods setObject:cachedParams forKey:NSStringFromSelector(sel)];
    }
    
    /*
     cachedMethods，当前类缓存的方法和参数列表
     {
        selname : // 其中某个方法的参数列表
            {    
            hash : <<[p1, p2, p3]>>,
            hash : <<[p1, p2]>>
        }
     }
     */
    NSString *hashKey = [self hashKeyForParams:params];
    [cachedParams setObject:params forKey:hashKey];
}

（3）扩展UIKit（UIButton+Theme等），新增换肤方法

- (void)setImageWithIdentifier:(NSString *)identifier forState:(UIControlState)state
{
    //  1、注册通知
    [self registerThemeChangeNotification];

    // 2、执行原始方法
    UIImage *image = [ThemeManager sharedManager].themeInfos[identifier];
    [self setImage:image forState:state];
    
    // 3、缓存方法及参数    
    [self cacheParams:@[identifier.imageType, @(state)] forSelector:@selector(setImage:forState:)];
}

（4）ThemeManager发送换肤通知，遍历执行缓存的换肤方法

- (void)performAllCachedSelector
{
   for (NSString *selName in [self.cachedMethods allKeys])
    {
        for (NSArray *params in [self.cachedMethods[selName] allValues])
        {
            [self performSelector:NSSelectorFromString(selName) params:params];
        }
    }
}

3、方案3

3.1、架构

方案3.png

3.2、实现

（1）设计一套皮肤文件配置协议

（2）设计一套方法映射管理协议

（3）扩展UIView（UIView+Theme），添加换肤方法，保存对应关系《MapID — SkinID》

- (void)setThemeMap:(NSDictionary *)themeMap
{  
    // 1、保存对应关系
    objc_setAssociatedObject(self, &kUIView_ThemeMap, themeMap, OBJC_ASSOCIATION_COPY_NONATOMIC);
    
    if (themeMap) {
        // 2、注册通知
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(themeChanged) name:kThemeDidChangeNotification object:nil];
        
        // 3、执行换肤方法
        [self themeChanged];
    }
    else {
        [[NSNotificationCenter defaultCenter] removeObserver:self name:kThemeDidChangeNotification object:nil];
    }
}

（4）应用层初始化UI组件，例如UIButton

- (void)viewDidLoad {
    [super viewDidLoad];
    
    UIButton *btn = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    
    btn.themeMap = 
@{kThemeButtonNormalImage : @"com.ac.image.button.normal",
kThemeButtonSelectedImage : @“com.ac.image.button.selected"};
    [self.view addSubview:btn];
}

（5）ThemeManager发送换肤通知，执行换肤方法

- (void)themeChanged
{
    NSDictionary *map = self.themeMap;
    if ([self isKindOfClass:[UIButton class]]) {
       UIButton *obj = (UIButton *)self;
       if (map[kThemeButtonNormalImage]) {
            NSString *skinId = map[kThemeButtonNormalImage];
            UIImage *image = [ThemeManager sharedInstance].themeConfig[skinId];
            [obj setImage:image forState:UIControlStateNormal];
       }
          if (map[kThemeButtonSelectedImage]) {
            NSString *skinId = map[kThemeButtonSelectedImage];
            UIImage *image = [ThemeManager sharedInstance].themeConfig[skinId];
            [obj setImage:image forState:UIControlStateSelected];
       }
    }

    TODO: 遍历执行其他UIKit控件的方法，例如UILabel
}

4、方案对比

4.1、分析

从架构层面来看，这3种方案的实现思路基本一致，具备相同的优点：
（1）利用通知或Block机制，解耦模块；
（2）皮肤文件利用ID特性，方便维护扩展；
（3）利用Category特性，对现有代码改动较小；
唯一的区别在于方法缓存器的设计和实现，这直接影响到换肤框架对App内存的消耗，可通过Demo分析这3种方案的内存占用。

4.2、案例

    // 方案1
    UIButton *testBtn = [[UIButton alloc] initWithFrame:CGRectMake(100, 100, 120, 75)];
    [testBtn them_setImageName:@"normalImage" forState:UIControlStateNormal];
    [[ThemEngine sharedInstance].themUI addObject:testBtn]; // 缓存对象
    [self.view addSubview:testBtn];
    
    // 方案2
    UIButton *testBtn = [[UIButton alloc] initWithFrame:CGRectMake(100, 100, 120, 75)];
    [testBtn setImageWithIdentifier:@"normalImage" forState:UIControlStateNormal];
    [self.view addSubview:testBtn];
    
    // 方案3
    UIButton *testBtn = [[UIButton alloc] initWithFrame:CGRectMake(100, 100, 120, 75)];
testBtn.themeMap = 
@{kThemeButtonNormalImage : @"normalImage"};
    [self.view addSubview:testBtn];

实验结果：

|方案1 |方案2 |方案3
---------|------|--------|------
内存消耗 |752 bytes |472 bytes |372 bytes

4.3、对方案3的改进：提高API的易用性

// 方案3
testBtn.themeMap = 
@{kThemeButtonNormalImage : @"normalImage"};

// 方案3改进
[testBtn setImageWithThemeId:@"normalImage" forState:UIControlStateNormal];

5、参考资料

（1）https://github.com/JyHu/EasyTheme
（2）https://github.com/jiecao-fm/SwiftTheme
（3）https://github.com/yanjunz/ThemeManager

如果读者有更好的方案，欢迎留言，一起讨论。