Ios NSDictionary<；FBGraphUser>*用户语法解释

在Facebook iOS SDK中，将使用以下处理程序返回请求：

 ^(FBRequestConnection *connection, 
       NSDictionary<FBGraphUser> *user, 
       NSError *error) { }

此语法与作为公共属性声明的语法

id object

语法有些相似，只是NSDictionary明确地是id对象，并且该字典符合协议？但是dot语法从何而来，如何声明任意NSFoundation对象与协议相对应，而不将对象本身子类化并使其一致

我做了一些额外的研究，似乎不可能在字典中添加一个类别就在字典中使用点符号。但是，我在中没有看到任何语法参考，以表明NSDictionary的这个特定实例符合该符号

Facebook的文档中很少有关于这种包装的工作原理：

FBGraphUser协议代表最常用的属性 Facebook用户对象的。它可用于访问NSD字典 已用FBGraphObject外观包装的对象

如果按照这条线索找到FBGraphObject文档，那么有一些方法返回符合此“facade…”的词典，但没有进一步解释如何包装词典

所以我想我的问题是：

底层代码是什么样子的 语法工作

它为什么存在

为什么facebook会以这种方式实施，而不仅仅是 制作一个他们可以将数据转换成的对象

任何解释或见解都将不胜感激

此语法与syntax id object语法有些相似

“有些相似”？“一模一样”怎么样

而且字典符合协议

不，声明说您必须传入一个对象，该对象的类是

NSDictionary

，同时它符合

FBGraphUser

协议

但是点语法是从哪里来的呢

我不明白。它来自于编写有问题代码的程序员。这是可能的，因为

FBGraphUser

协议声明了一些属性，然后可以通过点表示法访问这些属性

如何声明任意NSFoundation对象与协议相对应，而不将对象本身子类化并使其符合

这不是所谓的“NS粉底”，只是基础。它不是不“符合”协议的对象，而是它的类。你自己也展示了它的语法

它是如何实施的？简单：一个类别

#import <Foundation/Foundation.h>

@protocol Foo
@property (readonly, assign) int answer;
@end

@interface NSDictionary (MyCategory) <Foo>
@end

@implementation NSDictionary (MyCategory)

- (int)answer
{
    return 42;
}

@end

int main()
{
    NSDictionary *d = [NSDictionary dictionary];
    NSLog(@"%d", d.answer);
    return 0;
}

#导入
@协议Foo
@属性（只读，赋值）int-answer；
@结束
@接口字典（MyCategory）
@结束
@实现NSDictionary（MyCategory）
-（int）答案
{
返回42；
}
@结束
int main（）
{
NSDictionary*d=[NSDictionary dictionary]；
NSLog（@“%d”，d.答案）；
返回0；
}

这是一个SSCCE，i。E它按原样编译和运行，试试看

要使这种语法正常工作，底层代码是什么样子的

上面回答

它为什么存在

因为语言是这样定义的

facebook为什么要以这种方式实现它，而不是仅仅制作一个他们可以将数据转换成的对象

---

我不知道，问问Facebook的家伙。

基本上，

NSDictionary*user

，意味着一个对象继承自

NSDictionary

，添加了

FBGraphUser

协议声明的功能（特别是键入访问）

这种方法背后的原因在中有相当详细的描述（

FBGraphUser

协议扩展了

FBGraphObject

协议）。可能让您感到困惑的是，

FBGraphObject

是一个协议（已描述）和一个类（已描述），它继承自

NSMutableDictionary

就内部实现而言，这是一些非常高级的Objective-C动态魔法，您可能不想担心。您需要知道的是，如果愿意，您可以将该对象视为字典，或者使用协议中的其他方法。如果您确实想了解详细信息，可以查看以下方法，尤其是：

#pragma mark -
#pragma mark NSObject overrides

// make the respondsToSelector method do the right thing for the selectors we handle
- (BOOL)respondsToSelector:(SEL)sel
{
    return  [super respondsToSelector:sel] ||
    ([FBGraphObject inferredImplTypeForSelector:sel] != SelectorInferredImplTypeNone);
}

- (BOOL)conformsToProtocol:(Protocol *)protocol {
    return  [super conformsToProtocol:protocol] ||
    ([FBGraphObject isProtocolImplementationInferable:protocol 
                           checkFBGraphObjectAdoption:YES]);
}

// returns the signature for the method that we will actually invoke
- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel {
    SEL alternateSelector = sel;

    // if we should forward, to where?
    switch ([FBGraphObject inferredImplTypeForSelector:sel]) {
        case SelectorInferredImplTypeGet:
            alternateSelector = @selector(objectForKey:);
            break;
        case SelectorInferredImplTypeSet:
            alternateSelector = @selector(setObject:forKey:);
            break;
        case SelectorInferredImplTypeNone:
        default:
            break;
    }

    return [super methodSignatureForSelector:alternateSelector];
}

// forwards otherwise missing selectors that match the FBGraphObject convention
- (void)forwardInvocation:(NSInvocation *)invocation {
    // if we should forward, to where?
    switch ([FBGraphObject inferredImplTypeForSelector:[invocation selector]]) {
        case SelectorInferredImplTypeGet: {
            // property getter impl uses the selector name as an argument...
            NSString *propertyName = NSStringFromSelector([invocation selector]);
            [invocation setArgument:&propertyName atIndex:2];
            //... to the replacement method objectForKey:
            invocation.selector = @selector(objectForKey:);
            [invocation invokeWithTarget:self];
            break;
        }
        case SelectorInferredImplTypeSet: {
            // property setter impl uses the selector name as an argument...
            NSMutableString *propertyName = [NSMutableString stringWithString:NSStringFromSelector([invocation selector])];
            // remove 'set' and trailing ':', and lowercase the new first character
            [propertyName deleteCharactersInRange:NSMakeRange(0, 3)];                       // "set"
            [propertyName deleteCharactersInRange:NSMakeRange(propertyName.length - 1, 1)]; // ":"

            NSString *firstChar = [[propertyName substringWithRange:NSMakeRange(0,1)] lowercaseString];
            [propertyName replaceCharactersInRange:NSMakeRange(0, 1) withString:firstChar];
            // the object argument is already in the right place (2), but we need to set the key argument
            [invocation setArgument:&propertyName atIndex:3];
            // and replace the missing method with setObject:forKey:
            invocation.selector = @selector(setObject:forKey:);
            [invocation invokeWithTarget:self]; 
            break;
        } 
        case SelectorInferredImplTypeNone:
        default: 
            [super forwardInvocation:invocation];
            return;
    }
}

---

jbat100我可以在Facebook SDK范围之外的其他方式中使用FBGraphObject，因为该功能非常有用。我提出了一个问题。谢谢

#pragma mark -
#pragma mark NSObject overrides

// make the respondsToSelector method do the right thing for the selectors we handle
- (BOOL)respondsToSelector:(SEL)sel
{
    return  [super respondsToSelector:sel] ||
    ([FBGraphObject inferredImplTypeForSelector:sel] != SelectorInferredImplTypeNone);
}

- (BOOL)conformsToProtocol:(Protocol *)protocol {
    return  [super conformsToProtocol:protocol] ||
    ([FBGraphObject isProtocolImplementationInferable:protocol 
                           checkFBGraphObjectAdoption:YES]);
}

// returns the signature for the method that we will actually invoke
- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel {
    SEL alternateSelector = sel;

    // if we should forward, to where?
    switch ([FBGraphObject inferredImplTypeForSelector:sel]) {
        case SelectorInferredImplTypeGet:
            alternateSelector = @selector(objectForKey:);
            break;
        case SelectorInferredImplTypeSet:
            alternateSelector = @selector(setObject:forKey:);
            break;
        case SelectorInferredImplTypeNone:
        default:
            break;
    }

    return [super methodSignatureForSelector:alternateSelector];
}

// forwards otherwise missing selectors that match the FBGraphObject convention
- (void)forwardInvocation:(NSInvocation *)invocation {
    // if we should forward, to where?
    switch ([FBGraphObject inferredImplTypeForSelector:[invocation selector]]) {
        case SelectorInferredImplTypeGet: {
            // property getter impl uses the selector name as an argument...
            NSString *propertyName = NSStringFromSelector([invocation selector]);
            [invocation setArgument:&propertyName atIndex:2];
            //... to the replacement method objectForKey:
            invocation.selector = @selector(objectForKey:);
            [invocation invokeWithTarget:self];
            break;
        }
        case SelectorInferredImplTypeSet: {
            // property setter impl uses the selector name as an argument...
            NSMutableString *propertyName = [NSMutableString stringWithString:NSStringFromSelector([invocation selector])];
            // remove 'set' and trailing ':', and lowercase the new first character
            [propertyName deleteCharactersInRange:NSMakeRange(0, 3)];                       // "set"
            [propertyName deleteCharactersInRange:NSMakeRange(propertyName.length - 1, 1)]; // ":"

            NSString *firstChar = [[propertyName substringWithRange:NSMakeRange(0,1)] lowercaseString];
            [propertyName replaceCharactersInRange:NSMakeRange(0, 1) withString:firstChar];
            // the object argument is already in the right place (2), but we need to set the key argument
            [invocation setArgument:&propertyName atIndex:3];
            // and replace the missing method with setObject:forKey:
            invocation.selector = @selector(setObject:forKey:);
            [invocation invokeWithTarget:self]; 
            break;
        } 
        case SelectorInferredImplTypeNone:
        default: 
            [super forwardInvocation:invocation];
            return;
    }
}