iOS底層-KVC使用實踐以及實現原理

1. 最簡單的使用例子

• 假設有CYXModel類與CYXShopModel類，CYXModel裡面有name、product屬性，CYXShopModel裡面有productName屬性。
  
  Objective-C

  @interface CYXModel: NSObject @property (nonatomic, strong) NSString *name; @property (nonatomic, strong) CYXShopModel *product; @end

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  @interface CYXModel: NSObject @property (nonatomic, strong) NSString *name; @property (nonatomic, strong) CYXShopModel *product; @end

  
  
  Objective-C

  @interface CYXShopModel: NSObject @property (nonatomic, strong) NSString * productName; @end

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  @interface CYXShopModel: NSObject @property (nonatomic, strong) NSString * productName; @end

  • 不使用KVC，我們這樣訪問CYXModel的屬性
    • 取值：
      
      Objective-C

      CYXModel *model = [[CYXModel alloc]init]; NSString *name = model. name; CYXShopModel *shop = model. product; NSString *productName = shop. productName;

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      CYXModel *model = [[CYXModel alloc]init]; NSString *name = model. name; CYXShopModel *shop = model. product; NSString *productName = shop. productName;

    • 設值：
      
      Objective-C

      CYXModel *model = [[CYXModel alloc]init]; model. name = @"CYX"; CYXShopModel *shopModel = [[CYXShopModel alloc]init]; shopModel. productName = @"NIKE"; model. product = shopModel;

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      CYXModel *model = [[CYXModel alloc]init]; model. name = @"CYX"; CYXShopModel *shopModel = [[CYXShopModel alloc]init]; shopModel. productName = @"NIKE"; model. product = shopModel;

  • 使用KVC，我們可以這樣訪問CYXModel的屬性
    • 取值：
      
      Objective-C

      CYXModel *model = [[CYXModel alloc]init]; NSString *name = [model valueForKey: @"name" ]; NSString *productName = [model valueForKeyPath: @"product.productName" ];

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      CYXModel *model = [[CYXModel alloc]init]; NSString  *name = [model valueForKey: @"name" ]; NSString  *productName = [model valueForKeyPath: @"product.productName" ];

    • 設值：
      
      Objective-C

      CYXModel *model = [[CYXModel alloc]init]; [model setValue:@"CYX" forKey:@"name"]; [model setValue:@"NIKE" forKeyPath:@"product.productName"];

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      CYXModel *model = [[CYXModel alloc]init]; [model setValue:@"CYX" forKey:@"name"]; [model setValue:@"NIKE" forKeyPath:@"product.productName"];

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  注： 這個簡單的例子，可能你看了覺得這並沒什麼卵用，下面我們來分析一下稍微有點卵用的例子吧。

  2. KVC字典轉模型的實現原理

  • 假設dict字典中有name，icon的Key，CYXModel模型類中必須要有同名的name，icon屬性與之相對應。
  • 我們使用[CYXModel setValuesForKeysWithDictionary:dict];進行字典轉模型。
  • setValuesForKeysWithDictionary:方法內部實現原理如下：
    • (1) 遍歷字典裡面所有的key和值，name，icon。
      
      Objective-C

      // enumerateKeysAndObjectsUsingBlock:遍歷字典中的所有keys和valus [dict enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) { // 利用KVC給模型中屬性賦值,, // key:用來給哪個屬性 // Value:給模型的值 [CYXModel setValue:obj forKey:key]; }];

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      // enumerateKeysAndObjectsUsingBlock:遍歷字典中的所有keys和valus [dict enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {   // 利用KVC給模型中屬性賦值,,   // key:用來給哪個屬性   // Value:給模型的值   [CYXModel setValue:obj forKey:key]; }];

    • (2) 分別給屬性賦值
      • [CYXModel setValue:dict[@"name"] forKey:@"name"];
      • [CYXModel setValue:dict[@"icon"] forKey:@"icon"];
  • setValue:forKey:方法：給模型的屬性賦值
    • 賦值原理：
      • （1）去模型中查詢有沒有setIcon方法,就直接呼叫這個set方法,給模型這個屬性賦值[self setIcon:dict[@"icon"]];
      • （2）如果找不到set方法，接著就會去尋找有沒有icon屬性,如果有,就直接訪問模型中icon = dict[@"icon"];
      • （3）如果找不到icon屬性，接著又會去尋找_icon屬性,如果有,直接_icon = dict[@"icon"];
      • （4）如果都找不到就會報錯
        [<Flag 0x7fb74bc7a2c0> setValue:forUndefinedKey:]
  • 擴充套件：讀者可以去查查KVV（鍵值驗證），進一步理解報錯原因與容錯方法。

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  注： 稍微有點卵用的看完，接下來說一個比較有卵用的用法，這個例子需要配合runtime來實現，有興趣可以看看，runtime內容不少，這裡就暫不介紹了，歡迎 關注，在下篇文字小結一下runtime。

  3. 修改系統控制元件內部屬性（runtime + KVC）

  • 有時候，UI會閒著沒事，會給你找點事情，例如，介面設計圖是這樣的：
    

    必奢商城首頁
  • 這。。怎麼感覺有點不同，這UIPageControl怎麼跟我平常用的不一樣？平常不都是這樣的？？如下圖
    

    美麗說首頁
  • 首先想到的肯定是，檢視UIPageControl的標頭檔案，如下：
    
    Objective-C

    NS_CLASS_AVAILABLE_IOS(2_0) @interface UIPageControl : UIControl @property(nonatomic) NSInteger numberOfPages; // default is 0 @property(nonatomic) NSInteger currentPage; // default is 0. value pinned to 0..numberOfPages-1 @property(nonatomic) BOOL hidesForSinglePage; // hide the the indicator if there is only one page. default is NO @property(nonatomic) BOOL defersCurrentPageDisplay; // if set, clicking to a new page won't update the currently displayed page until -updateCurrentPageDisplay is called. default is NO - (void)updateCurrentPageDisplay; // update page display to match the currentPage. ignored if defersCurrentPageDisplay is NO. setting the page value directly will update immediately - (CGSize)sizeForNumberOfPages:(NSInteger)pageCount; // returns minimum size required to display dots for given page count. can be used to size control if page count could change @property(nullable, nonatomic,strong) UIColor *pageIndicatorTintColor NS_AVAILABLE_IOS(6_0) UI_APPEARANCE_SELECTOR; @property(nullable, nonatomic,strong) UIColor *currentPageIndicatorTintColor NS_AVAILABLE_IOS(6_0) UI_APPEARANCE_SELECTOR; @end

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    NS_CLASS_AVAILABLE_IOS(2_0) @interface UIPageControl : UIControl   @property(nonatomic) NSInteger numberOfPages;          // default is 0 @property(nonatomic) NSInteger currentPage;            // default is 0. value pinned to 0..numberOfPages-1   @property(nonatomic) BOOL hidesForSinglePage;          // hide the the indicator if there is only one page. default is NO   @property(nonatomic) BOOL defersCurrentPageDisplay;    // if set, clicking to a new page won't update the currently displayed page until -updateCurrentPageDisplay is called. default is NO - (void)updateCurrentPageDisplay;                      // update page display to match the currentPage. ignored if defersCurrentPageDisplay is NO. setting the page value directly will update immediately   - (CGSize)sizeForNumberOfPages:(NSInteger)pageCount;   // returns minimum size required to display dots for given page count. can be used to size control if page count could change   @property(nullable, nonatomic,strong) UIColor *pageIndicatorTintColor NS_AVAILABLE_IOS(6_0) UI_APPEARANCE_SELECTOR; @property(nullable, nonatomic,strong) UIColor *currentPageIndicatorTintColor NS_AVAILABLE_IOS(6_0) UI_APPEARANCE_SELECTOR;   @end

  • 臥槽，就這麼幾個屬性可以給我設的，不夠用啊兄弟。能不能給我個可以賦值UIImage物件的屬性？看來正常途徑使用系統的控制元件是設不了了，剩下的我感覺只有兩種方法（如有其它，歡迎指出），一種是自定義PageControl，這種方式看起來不簡單，各位有興趣可以去試試。另一種方式就是，通過runtime遍歷出UIPageControl所有屬性（包括私有成員屬性，runtime確實很強大）。
  • 使用runtime遍歷UIPageControl結果（下篇文字再談談runtime，這裡暫不解釋）如下列印：
    
    2016-03-23 01:09:26.161 TenMinDemo[6224:507269] UIPageControl -> _lastUserInterfaceIdiom = q 2016-03-23 01:09:26.161 TenMinDemo[6224:507269] UIPageControl -> _indicators = @"NSMutableArray" 2016-03-23 01:09:26.161 TenMinDemo[6224:507269] UIPageControl -> _currentPage = q 2016-03-23 01:09:26.161 TenMinDemo[6224:507269] UIPageControl -> _displayedPage = q 2016-03-23 01:09:26.162 TenMinDemo[6224:507269] UIPageControl -> _pageControlFlags = {?="hideForSinglePage"b1"defersCurrentPageDisplay"b1} 2016-03-23 01:09:26.162 TenMinDemo[6224:507269] UIPageControl -> _currentPageImage = @"UIImage" // 當前選中圖片 2016-03-23 01:09:26.162 TenMinDemo[6224:507269] UIPageControl -> _pageImage = @"UIImage" // 預設圖片 2016-03-23 01:09:26.162 TenMinDemo[6224:507269] UIPageControl -> _currentPageImages = @"NSMutableArray" 2016-03-23 01:09:26.162 TenMinDemo[6224:507269] UIPageControl -> _pageImages = @"NSMutableArray" 2016-03-23 01:09:26.162 TenMinDemo[6224:507269] UIPageControl -> _backgroundVisualEffectView = @"UIVisualEffectView" 2016-03-23 01:09:26.162 TenMinDemo[6224:507269] UIPageControl -> _currentPageIndicatorTintColor = @"UIColor" 2016-03-23 01:09:26.163 TenMinDemo[6224:507269] UIPageControl -> _pageIndicatorTintColor = @"UIColor" 2016-03-23 01:09:26.163 TenMinDemo[6224:507269] UIPageControl -> _legibilitySettings = @"_UILegibilitySettings" 2016-03-23 01:09:26.163 TenMinDemo[6224:507269] UIPageControl -> _numberOfPages = q

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    2016-03-23 01:09:26.161 TenMinDemo[6224:507269] UIPageControl -> _lastUserInterfaceIdiom = q 2016-03-23 01:09:26.161 TenMinDemo[6224:507269] UIPageControl -> _indicators = @"NSMutableArray" 2016-03-23 01:09:26.161 TenMinDemo[6224:507269] UIPageControl -> _currentPage = q 2016-03-23 01:09:26.161 TenMinDemo[6224:507269] UIPageControl -> _displayedPage = q 2016-03-23 01:09:26.162 TenMinDemo[6224:507269] UIPageControl -> _pageControlFlags = {?="hideForSinglePage"b1"defersCurrentPageDisplay"b1} 2016-03-23 01:09:26.162 TenMinDemo[6224:507269] UIPageControl -> _currentPageImage = @"UIImage" // 當前選中圖片 2016-03-23 01:09:26.162 TenMinDemo[6224:507269] UIPageControl -> _pageImage = @"UIImage" // 預設圖片 2016-03-23 01:09:26.162 TenMinDemo[6224:507269] UIPageControl -> _currentPageImages = @"NSMutableArray" 2016-03-23 01:09:26.162 TenMinDemo[6224:507269] UIPageControl -> _pageImages = @"NSMutableArray" 2016-03-23 01:09:26.162 TenMinDemo[6224:507269] UIPageControl -> _backgroundVisualEffectView = @"UIVisualEffectView" 2016-03-23 01:09:26.162 TenMinDemo[6224:507269] UIPageControl -> _currentPageIndicatorTintColor = @"UIColor" 2016-03-23 01:09:26.163 TenMinDemo[6224:507269] UIPageControl -> _pageIndicatorTintColor = @"UIColor" 2016-03-23 01:09:26.163 TenMinDemo[6224:507269] UIPageControl -> _legibilitySettings = @"_UILegibilitySettings" 2016-03-23 01:09:26.163 TenMinDemo[6224:507269] UIPageControl -> _numberOfPages = q

  • 結果非常滿意，果然找到我想要的圖片設定屬性。
  • 然後通過KVC設定自定義圖片，實現了效果，程式碼如下：
    
    Objective-C

    UIPageControl *pageControl = [[UIPageControl alloc] init]; [pageControl setValue:[UIImage imageNamed:@"home_slipt_nor"] forKeyPath:@"_pageImage"]; [pageControl setValue:[UIImage imageNamed:@"home_slipt_pre"] forKeyPath:@"_currentPageImage"];

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    UIPageControl *pageControl = [[UIPageControl alloc] init]; [pageControl setValue:[UIImage imageNamed:@"home_slipt_nor"] forKeyPath:@"_pageImage"]; [pageControl setValue:[UIImage imageNamed:@"home_slipt_pre"] forKeyPath:@"_currentPageImage"];

  • 注：
    這裡只是拋磚引玉的講了個小例子，其他的神奇功能等待讀者去發現啦。

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  提示： 在xib/Storyboard中，也可以使用KVC，下面是在xib中使用KVC把圖片邊框設定成圓角

  

  xib中設定KVC

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  • KVC就先說到這裡了，歡迎持續關注我的簡書或Github。