在 Objective C 中，如何通过反射找出方法的返回类型？

Question

@interface Foo : NSObject {
}

- (Bar)bar;

在运行时，给定[Foo class]，我们如何找出Foo所有方法的返回类型？

我已经研究 Objective-C 运行时 API 一段时间了；据我所知，没有办法获取方法或属性的返回类型（即类）。这似乎是任何反射 API 中的一个严重遗漏。

Answer 1

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)

Objective-C 运行时参考

首先，使用 class_getClassMethod 获取方法对象，

Method m = class_getClassMethod( [ SomeClass class ], @selector( someMethod ) );

然后使用method_getReturnType：

char ret[ 256 ];
method_getReturnType( m, ret, 256 );
NSLog( @"Return type: %s", ret );

Answer 2

您可以辨别基本信息，例如它是什么 C 类型，但无法区分返回类型上的各种实例类型（或类）。

Objective-C 从未被设计或意图具有这种程度的反射。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。

已经存在这样的情况：将 C++ 对象传递给 Objective-C 方法时，与方法参数化相关的元数据的数量级比生成的代码大（字面意思是单个方法调用的元数据的 MB 数） 。

---

参数/返回类型元数据形式的相对简单类型的示例：

{CGRect={CGPoint=dd}{CGSize=dd}}96@0:8@16{CGRect={CGPoint=dd}{CGSize=dd}}24{CGRect={CGPoint=dd}{CGSize=dd}}56q88

以及来自 WebKit 的一个特别令人震惊的示例：

^{文档=^^?^^?i^{ContainerNode}{Weak=^{JSValue}}^{文档}^{节点}^{节点}^{渲染对象}I^{节点}^{节点}^{TreeScope}{DocumentOrderedMap={HashMap,WTF::HashTraits,WTF::HashTraits

<块引用>

={哈希表，WTF::PairFirstExtractor
,WTF::PtrHash,WTF::PairHashTraits,
WTF::HashTraits
,WTF::哈希特征
=^{pair}iiii}}{HashCountedSet,WTF::HashTraits
={HashMap,WTF::HashTraits,WTF::HashTraits
={哈希表，WTF::PairFirstExtractor
,WTF::PtrHash,WTF::PairHashTraits,
WTF::HashTraits
,WTF::哈希特征
=^{pair}iiii}}}}{DocumentOrderedMap={HashMap,WTF::HashTraits,WTF::HashTraits
={哈希表，WTF::PairFirstExtractor
,WTF::PtrHash,WTF::PairHashTraits,
WTF::HashTraits
,WTF::哈希特征
=^{pair}iiii}}{HashCountedSet,WTF::HashTraits
={HashMap,WTF::HashTraits,WTF::HashTraits
={哈希表，WTF::PairFirstExtractor
,WTF::PtrHash,WTF::PairHashTraits,
WTF::HashTraits
,WTF::哈希特征
=^{pair}iiii}}}}I^^?{RefPtr=^{SecurityOrigin}}{HashSet,WTF::HashTraits
={哈希表，WTF::PtrHash，WTF::HashTraits，WTF::HashTraits
=^^{MessagePort}iiii}}{HashMap,WTF::HashTraits,WTF::HashTraits
={哈希表，WTF::PairFirstExtractor
,WTF::PtrHash,WTF::PairHashTraits,
WTF::HashTraits >,WTF::HashTraits
=^{pair}iiii}}BB{HashMap,WTF::HashTraits,WTF::HashTraits
={HashTable,WTF::PairFirstExtractor>,WTF::IntHash,WTF::PairHashTraits,
WTF::HashTraits >,WTF::HashTraits
=^{pair}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}}}b 1b1iiiiiiiiii}{KURL={String={RefPtr=^{StringImpl}}}b1b1iiiiiiiiii}{KURL={String={RefPtr=^{StringImpl}}}b1b1iiiiiiiiii}{String={RefPtr=^{StringImpl}}}{String ={回复fPtr=^{StringImpl}}}{RefPtr=^{DocumentType}}{OwnPtr=^{DOMImplementation}}iBiB{RefPtr=^{CSSStyleSheet}}{RefPtr=^{CSSStyleSheet}}{RefPtr=^{CSSStyleSheet}}{自己的Ptr，
0ul>
=^{向量,0ul>}}BBBBiB{Color=IB}{RefPtr=^{节点}}{RefPtr=^{节点}}{RefPtr=^{节点}}{RefPtr=^{元素}}Q{HashSet ,WTF::哈希特征
={哈希表，WTF::PtrHash，WTF::HashTraits，WTF::HashTraits
=^^{NodeIterator}iiii}}{HashSet，WTF::HashTraits
={哈希表，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^{文档}{?=^q}}BBBBBBBBBBBBBBBBBI{StringWithDirec化={String={RefPtr=^{StringImpl}}}i}{StringWithDirection={String={RefPtr=^{StringImpl}}}i}B{RefPtr=^{Element}}{OwnPtr=^{RenderArena}} ^{AXObjectCache}{OwnPtr=^{文档MarkerController}}{Timer=^^?ddiI^{文档}{?=^q}}^{元素}B{RefPtr=^{SerializedScriptValue}}dBi{OwnPtr=^{ScriptRunner}}{OwnPtr=^{TransformSource} {RefPtr=^{文档}}i {String={RefPtr=^{StringImpl}}}{String={RefPtr=^{StringImpl}}}B{String={RefPtr=^{StringImpl}}}^{RenderObject}{RefPtr=^{TextResourceDecoder}}i {CheckedRadioButtons={OwnPtr，，
WTF::哈希特征，
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::哈希特征
=^{pair*>}iiii}}{HashMap,WTF::PtrHash,WTF::HashTraits,WTF::HashTraits*>
={HashTable,std::pair*>,WTF::PairFirstExtractor*>
,WTF::PtrHash,WTF::PairHashTraits,
WTF::HashTraits*>
,WTF::哈希特征
=^{pair*>}iiii}}BB}]}{FixedArray,
WTF::哈希特征，
WTF::HashTraits
,2ul>=[2{HashMap,WTF::HashTraits,WTF::HashTraits
={哈希表，WTF::PairFirstExtractor
,WTF::PtrHash,WTF::PairHashTraits,
WTF::HashTraits
,WTF::哈希特征
=^{pair}iiii}}]}{RefPtr=^{XPathEvaluator}}{OwnPtr=^{SVGDocumentExtensions}}{Vector=Q{VectorBuffer=^{DashboardRegionValue}Q}}BB{HashMap,WTF::StringHash,WTF ::HashTraits，WTF::HashTraits

<块引用>

={哈希表
,WTF::PairFirstExtractor >
,WTF::StringHash,WTF::PairHashTraits,
WTF::HashTraits >
,WTF::哈希特征
=^{对
}iiii}}BB[1{IconURL=i{KURL={String={RefPtr=^{StringImpl}}}b1b1iiiiiiiiii}}]{HashSet，WTF::HashTraits
={哈希表，WTF::PtrHash，WTF::HashTraits，WTF::HashTraits
=^^{元素}iiii}}{HashSet，WTF::HashTraits
={哈希表，WTF::PtrHash，WTF::HashTraits，WTF::HashTraits
=^^{元素}iiii}}{HashSet，WTF::HashTraits
={哈希表，WTF::PtrHash，WTF::HashTraits，WTF::HashTraits
=^^{元素}iiii}}{HashMap，WTF::HashTraits
={哈希表，WTF::PairFirstExtractor
,WTF::CaseFoldingHash,WTF::PairHashTraits,
WTF::HashTraits >,WTF::HashTraits
=^{pair}iiii}}BBBBBBB{RefPtr=^{EventQueue}}{RefPtr=^{DocumentWeakReference}}{HashSet,WTF::HashTraits
={哈希表，WTF::PtrHash，WTF::HashTraits，WTF::HashTraits
=^^{MediaCanStartListener}iiii}}{QualifiedName=^{QualifiedNameImpl}}B{RefPtr=^{Element}}^{RenderFullScreen}{Timer=^^?ddiI^{文档}{?=^q}}{Deque ,0ul>=QQ{VectorBuffer,0ul>=^{RefPtr}Q}}B{IntRect={Int Point=ii}{IntSize=ii}}{RefPtr=^{RenderStyle}}i{Timer=^^?ddiI^{文档}{?=^q}}{ViewportArguments=fffffff}BB{DocumentTiming=ddddd}{RefPtr =^{MediaQueryMatcher}}BII{RefPtr=^{ContentSecurityPolicy}}}16@0:8