@interface Foo : NSObject {
}
- (Bar)bar;
在运行时，给定[Foo类]，我们如何找出Foo所有方法的返回类型？
我研究 Objective-C 运行时 API 已经有一段时间了；据我所知，没有办法获得方法或属性的返回类型（即类）。这似乎是任何反射 API 中的严重遗漏。
【问题讨论】：
标签： objective-c reflection runtime introspection
您可以使用 Objective-C 运行时函数：
Method class_getClassMethod(Class aClass, SEL aSelector)
void method_getReturnType(Method method, char *dst, size_t dst_len)
首先，获取方法对象，使用class_getClassMethod
Method m = class_getClassMethod( [ SomeClass class ], @selector( someMethod ) );
然后，使用method_getReturnType 询问返回类型：
char ret[ 256 ];
method_getReturnType( m, ret, 256 );
NSLog( @"Return type: %s", ret );
【讨论】：
您可以说出基本信息，例如它是什么 C 类型，但您无法区分返回类型上的各种实例类型（或类）。
Objective-C 从来没有被设计过，也没有打算有这种程度的反射。主要是因为这样做会大大增加可执行文件（所有元数据）的大小，并且支持所有 C 类型（想想 C++ 类型）的完整参数/返回类型元数据自省将非常复杂。
在某些情况下，当将 C++ 对象传递给 Objective-C 方法时，与方法参数化相关的元数据比生成的代码要大几个数量级（字面意思是——单个元数据的 MBs方法调用）。
argument/return-type 元数据形式的一个相对简单类型的例子：
{CGRect={CGPoint=dd}{CGSize=dd}}96@0:8@16{CGRect={CGPoint=dd}{CGSize=dd}}24{CGRect={CGPoint=dd}{CGSize=dd}}56q88
还有一个来自 WebKit 的特别令人震惊的例子：
^{Document=^^?^^?i^{ContainerNode}{Weak=^{JSValue}}^{Document}^{Node}^{Node}^{RenderObject}I^{Node}^{Node }^{TreeScope}{DocumentOrderedMap={HashMap,WTF::HashTraits,WTF::HashTraits
={HashTable,WTF::PairFirstExtractor ,WTF::PtrHash,WTF::PairHashTraits, WTF::HashTraits ,WTF::HashTraits =^{pair}iiii}}{HashCountedSet,WTF::HashTraits ={HashMap,WTF::HashTraits,WTF::HashTraits ={HashTable,WTF::PairFirstExtractor ,WTF::PtrHash,WTF::PairHashTraits, WTF::HashTraits ,WTF::HashTraits =^{pair}iiii}}}}{DocumentOrderedMap={HashMap,WTF::HashTraits,WTF::HashTraits ={HashTable,WTF::PairFirstExtractor ,WTF::PtrHash,WTF::PairHashTraits, WTF::HashTraits ,WTF::HashTraits =^{pair}iiii}}{HashCountedSet,WTF::HashTraits ={HashMap,WTF::HashTraits,WTF::HashTraits ={HashTable,WTF::PairFirstExtractor ,WTF::PtrHash,WTF::PairHashTraits, WTF::HashTraits ,WTF::HashTraits =^{pair}iiii}}}}I^^?{RefPtr=^{SecurityOrigin}}{HashSet,WTF::HashTraits ={HashTable,WTF::PtrHash,WTF::HashTraits,WTF::HashTraits =^^{MessagePort}iiii}}{HashMap,WTF::HashTraits,WTF::HashTraits ={HashTable,WTF::PairFirstExtractor ,WTF::PtrHash,WTF::PairHashTraits, WTF::HashTraits >,WTF::HashTraits =^{对}iiii}}BB{HashMap,WTF::HashTraits,WTF::HashTraits ={HashTable,WTF::PairFirstExtractor >,WTF::IntHash,WTF::PairHashTraits, WTF::HashTraits >,WTF::HashTraits =^{对}iiii}}B{OwnPtr, 0ul> =^{Vector,0ul>}}{RefPtr=^{DatabaseThread}}Bi{OwnPtr=^{CSSStyleSelector}}BB{RefPtr=^{CSSPrimitiveValueCache}}^{Frame}{OwnPtr=^{CachedResourceLoader}}{RefPtr= ^{DocumentParser}}B{KURL={String={RefPtr=^{StringImpl}}}b1b1iiiiiiiiii}{KURL={String={RefPtr=^{StringImpl}}}b1b1iiiiiiiiii}{KURL={String={RefPtr=^ {StringImpl}}}b1b1iiiiiiiiii}{KURL={String={RefPtr=^{StringImpl}}}b1b1iiiiiiiiii}{KURL={String={RefPtr=^{StringImpl}}}b1b1iiiiiiiiii}{String={RefPtr=^{StringImpl }}}{String={RefPtr=^{StringImpl}}}{RefPtr=^{DocumentType}}{OwnPtr=^{DOMImplementation}}iBiB{RefPtr=^{CSSStyleSheet}}{RefPtr=^{CSSStyleSheet}}{RefPtr =^{CSSStyleSheet}}{OwnPtr, 0ul> =^{Vector,0ul>}}BBBBiB{Color=IB}{RefPtr=^{Node}}{RefPtr=^{Node}}{RefPtr=^{Node}}{RefPtr=^{Element}}Q{HashSet ,WTF::HashTraits ={HashTable,WTF::PtrHash,WTF::HashTraits,WTF::HashTraits =^^{NodeIterator}iiii}}{HashSet,WTF::HashTraits ={HashTable,WTF::PtrHash,WTF::HashTraits,WTF::HashTraits =^^{范围}iiii}}S{RefPtr=^{StyleSheetList}}{ListHashSet ={HashTable,WTF::ListHashSetNode,WTF::IdentityExtractor*>,WTF::ListHashSetNodeHashFunctions ,WTF::HashTraits*>,WTF::HashTraits*> =^^{ListHashSetNode}iiii}^{ListHashSetNode}^{ListHashSetNode}{OwnPtr =^{ListHashSetNodeAllocator}}}{ListHashSet ={HashTable,WTF::ListHashSetNode,WTF::IdentityExtractor*>,WTF::ListHashSetNodeHashFunctions ,WTF::HashTraits*>,WTF::HashTraits*> =^^{ListHashSetNode}iiii}^{ListHashSetNode}^{ListHashSetNode}{OwnPtr =^{ListHashSetNodeAllocator}}}{ListHashSet ={HashTable,WTF::ListHashSetNode,WTF::IdentityExtractor*>,WTF::ListHashSetNodeHashFunctions ,WTF::HashTraits*>,WTF::HashTraits*> =^^{ListHashSetNode}iiii}^{ListHashSetNode}^{ListHashSetNode}{OwnPtr =^{ListHashSetNodeAllocator}}}{HashMap,WebCore::FormElementKeyHash,WebCore::FormElementKeyHashTraits,WTF::HashTraits > ={哈希表 ,WTF::PairFirstExtractor > ,WebCore::FormElementKeyHash,WTF::PairHashTraits > ,WebCore::FormElementKeyHashTraits>=^{对 }iiii}}{Color=IB}{Color=IB}{Color=IB}{String={RefPtr=^{StringImpl}}}{String={RefPtr=^{StringImpl}}}BBiB{Timer=^^? ddiI^{Document}{?=^q}}BBBBBBBBBBBBBBBBBI{StringWithDirection={String={RefPtr=^{StringImpl}}}i}{StringWithDirection={String={RefPtr=^{StringImpl}}}i}B{RefPtr =^{Element}}{OwnPtr=^{RenderArena}}^{AXObjectCache}{OwnPtr=^{DocumentMarkerController}}{Timer=^^?ddiI^{Document}{?=^q}}^{Element}B{ RefPtr=^{SerializedScriptValue}}dBi{OwnPtr=^{ScriptRunner}}{OwnPtr=^{TransformSource}}{RefPtr=^{Document}}i{String={RefPtr=^{StringImpl}}}{String={RefPtr =^{StringImpl}}}B{String={RefPtr=^{StringImpl}}}^{RenderObject}{RefPtr=^{TextResourceDecoder}}i{CheckedRadioButtons={OwnPtr, WTF::HashTraits, WTF::HashTraits > =^{HashMap,WTF::HashTraits,WTF::HashTraits }}}{FixedArray=[10{CollectionCache=Q^{Element}IIi{HashMap,WTF::PtrHash,WTF::HashTraits,WTF::HashTraits*> ={HashTable,std::pair*>,WTF::PairFirstExtractor*> ,WTF::PtrHash,WTF::PairHashTraits, WTF::HashTraits*> ,WTF::HashTraits =^{pair*>}iiii}}{HashMap,WTF::PtrHash,WTF::HashTraits,WTF::HashTraits*> ={HashTable,std::pair*>,WTF::PairFirstExtractor*> ,WTF::PtrHash,WTF::PairHashTraits, WTF::HashTraits*> ,WTF::HashTraits =^{pair*>}iiii}}BB}]}{FixedArray, WTF::HashTraits, WTF::HashTraits ,2ul>=[2{HashMap,WTF::HashTraits,WTF::HashTraits ={HashTable,WTF::PairFirstExtractor ,WTF::PtrHash,WTF::PairHashTraits, WTF::HashTraits ,WTF::HashTraits =^{pair}iiii}}]}{RefPtr=^{XPathEvaluator}}{OwnPtr=^{SVGDocumentExtensions}}{Vector=Q{VectorBuffer=^{DashboardRegionValue}Q}}BB{HashMap,WTF::StringHash,WTF ::HashTraits,WTF::HashTraits
={哈希表 ,WTF::PairFirstExtractor > ,WTF::StringHash,WTF::PairHashTraits, WTF::HashTraits > ,WTF::HashTraits =^{对 }iiii}}BB[1{IconURL=i{KURL={String={RefPtr=^{StringImpl}}}b1b1iiiiiiiiii}}]{HashSet,WTF::HashTraits ={HashTable,WTF::PtrHash,WTF::HashTraits,WTF::HashTraits =^^{元素}iiii}}{HashSet,WTF::HashTraits ={HashTable,WTF::PtrHash,WTF::HashTraits,WTF::HashTraits =^^{元素}iiii}}{HashSet,WTF::HashTraits ={HashTable,WTF::PtrHash,WTF::HashTraits,WTF::HashTraits =^^{元素}iiii}}{HashMap,WTF::HashTraits ={HashTable,WTF::PairFirstExtractor ,WTF::CaseFoldingHash,WTF::PairHashTraits, WTF::HashTraits >,WTF::HashTraits =^{pair}iiii}}BBBBBBB{RefPtr=^{EventQueue}}{RefPtr=^{DocumentWeakReference}}{HashSet,WTF::HashTraits ={HashTable,WTF::PtrHash,WTF::HashTraits,WTF::HashTraits =^^{MediaCanStartListener}iiii}}{QualifiedName=^{QualifiedNameImpl}}B{RefPtr=^{Element}}^{RenderFullScreen}{Timer=^^?ddiI^{Document}{?=^q}}{Deque ,0ul>=QQ{VectorBuffer,0ul>=^{RefPtr}Q}}B{IntRect={IntPoint=ii}{IntSize=ii}}{RefPtr=^{RenderStyle}}i{Timer=^^?ddiI^ {Document}{?=^q}}{ViewportArguments=fffffff}BB{DocumentTiming=ddddd}{RefPtr=^{MediaQueryMatcher}}BII{RefPtr=^{ContentSecurityPolicy}}}16@0:8
【讨论】：