DKNightVersion夜间模式实现原理

DKNightVersion夜间模式实现的最基本原理:每一种类型的控件注册通知,当用户点击夜间模式时,发送通知,然后各控件响应通知方法,更改颜色.

1. 注册通知,添加通知响应方法.通过给根类NSObject(必须是根类里)添加类别Night,在类别里添加属性pickers.初始化pickers时,注册通知.并在类别里添加通知响应方法- (void)night_updateColor.

   @implementation NSObject (Night)
   
   - (NSMutableDictionary<NSString *, DKColorPicker> *)pickers {
       NSMutableDictionary<NSString *, DKColorPicker> *pickers = objc_getAssociatedObject(self, @selector(pickers));
       if (!pickers) {
           
           @autoreleasepool {
               // Need to removeObserver in dealloc
               if (objc_getAssociatedObject(self, &DKViewDeallocHelperKey) == nil) {
                   __unsafe_unretained typeof(self) weakSelf = self; // NOTE: need to be __unsafe_unretained because __weak var will be reset to nil in dealloc
                   id deallocHelper = [self addDeallocBlock:^{
                       [[NSNotificationCenter defaultCenter] removeObserver:weakSelf];
                   }];
                   objc_setAssociatedObject(self, &DKViewDeallocHelperKey, deallocHelper, OBJC_ASSOCIATION_ASSIGN);
               }
           }
   
           pickers = [[NSMutableDictionary alloc] init];
           objc_setAssociatedObject(self, @selector(pickers), pickers, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
           
           [[NSNotificationCenter defaultCenter] removeObserver:self name:DKNightVersionThemeChangingNotification object:nil];
   
           [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(night_updateColor) name:DKNightVersionThemeChangingNotification object:nil];
       }
       return pickers;
   }
   
   - (void)night_updateColor {
       [self.pickers enumerateKeysAndObjectsUsingBlock:^(NSString * _Nonnull selector, DKColorPicker  _Nonnull picker, BOOL * _Nonnull stop) {
           SEL sel = NSSelectorFromString(selector);
           id result = picker(self.dk_manager.themeVersion);
           [UIView animateWithDuration:DKNightVersionAnimationDuration
                            animations:^{
   #pragma clang diagnostic push
   #pragma clang diagnostic ignored "-Warc-performSelector-leaks"
                                [self performSelector:sel withObject:result];
   #pragma clang diagnostic pop
                            }];
       }];
   }
   
   

2. 注册通知时机.提供另外的设置背景色的方法dk_setBackgroundColorPicker.使用之前的属性self.pickers,保存背景色,self.pickers在初始化时会注册通知.

   - (void)dk_setBackgroundColorPicker:(DKColorPicker)picker {
       objc_setAssociatedObject(self, @selector(dk_backgroundColorPicker), picker, OBJC_ASSOCIATION_COPY_NONATOMIC);
       self.backgroundColor = picker(self.dk_manager.themeVersion);
       [self.pickers setValue:[picker copy] forKey:@"setBackgroundColor:"];
   }
   

3. 发送通知,更改主题.作者是通过提供一个@property (nonatomic, strong) DKThemeVersion *themeVersion;themeVersion属性,在设置的时候发送通知.

   - (void)setThemeVersion:(DKThemeVersion *)themeVersion {
       if ([_themeVersion isEqualToString:themeVersion]) {
           // if type does not change, don't execute code below to enhance performance.
           return;
       }
       _themeVersion = themeVersion;
   
       // Save current theme version to user default
       [[NSUserDefaults standardUserDefaults] setValue:themeVersion forKey:DKNightVersionCurrentThemeVersionKey];
       [[NSNotificationCenter defaultCenter] postNotificationName:DKNightVersionThemeChangingNotification
                                                           object:nil];
   
       if (self.shouldChangeStatusBar) {
   #pragma clang diagnostic push
   #pragma clang diagnostic ignored "-Wdeprecated-declarations"
           if ([themeVersion isEqualToString:DKThemeVersionNight]) {
               [[UIApplication sharedApplication] setStatusBarStyle:UIStatusBarStyleLightContent];
           } else {
               [[UIApplication sharedApplication] setStatusBarStyle:UIStatusBarStyleDefault];
           }
   #pragma clang diagnostic pop
       }
   

}
```

DKNightVersion中有几点是值得学习的:

• 作者并没有在每个控件初始化的时候注册通知.在每个控件初始化的时候注册通知不仅繁琐,而且没办法进行封装.所以必须找到一个总入口,在那里进行通知的注册.
• 尽可能少的代码侵入性,通过类别可以实现最少的代码侵入性.通过给根类添加类别,再通过runtime添加属性.这样就有了一个总入口,因为每个类都是继承自NSObject的.
• 作者将通知的注册和通知的发送都封装在设置属性里,很好的隐藏了实现的细节.