在Objective C中，如何通過反射找出方法的返回類型？

Question

@interface Foo : NSObject { 
} 

- (Bar)bar; 

在運行時，給定[Foo class]，我們如何找出Foo所有方法的返回類型？

我一直在研究Objective-C運行時API一段時間;據我所知，無法獲得方法或屬性的返回類型（即Class）。這似乎是任何反射API中的嚴重遺漏。

Answer 1

您可以告訴基本信息，例如它是什麼類型的C，但是您不能區分返回類型上的各種實例類型（或類）。 Objective-C從來沒有設計過，也沒有打算有這樣的反思水平。主要是因爲這樣做會大大增加可執行文件的大小（所有元數據）並支持所有C類型的全參數/返回類型元數據自省 - 認爲C++類型 - 會非常複雜。

在將C++對象傳遞給Objective-C方法時，已經出現過與方法參數化相關的元數據量級大於生成的代碼的情況（字面上 - 元數據的MB值爲a單一方法調用）。

---

在參數相對簡單的類型的一個例子/返回類型的元數據的形式：

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

而且從WebKit的一個特別突出的例子：

^{文獻=^^ ^^？I^{ContainerNode} {弱=^{JSValue}}^{}文獻^ {}節點^ {}節點^ {渲染對象} I^{}節點^ {}節點^ {TreeScope} {DocumentOrderedMap = {HashMap，WTF :: HashTraits，WTF :: HashTraits

= {哈希表，WTF :: PairFirstExtractor ，WTF :: PtrHash，WTF :: PairHashTraits， WTF :: HashTraits ，WTF :: HashTraits =^{對} IIII}} {HashCountedSet，WTF :: HashTraits = {HashMap中，WTF :: HashTraits，WTF :: HashTraits = {哈希表，WTF :: PairFirstExtractor ，WTF :: PtrHash，WTF :: PairHashTraits， WTF :: HashTraits ，WTF :: HashTraits =^{對} iiii}}}} {DocumentOrderedMap = {HashMap，WTF :: HashTraits，WTF :: HashTraits = {HashTable，WTF :: PairFirstExtractor ，WTF :: PtrHash，WTF :: PairHashTraits， WTF :: HashTraits ，WTF :: HashTraits =^{對} IIII}} {HashCountedSet，WTF :: HashTraits = {HashMap中，WTF :: HashTraits，WTF :: HashTraits = {哈希表，WTF :: PairFirstExtractor ，WTF :: WTF :: HashTraits =^{pair} iiii}}}} WT^:: HashTraits ，{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 =^{pair} iiii}} BB {HashMap ，WTF :: HashTraits，WTF :: HashTraits = {HashTable，WTF :: PairFirstExtractor>，WTF :: IntHash，WTF :: PairHashTraits， WTF :: HashTraits>，WTF :: HashTraits =^{pair} iiii} } {{OwnPtr， 0ul> =^{Vector，0ul>}} {RefPtr =^{DatabaseThread}} Bi {OwnPtr =^{CSSStyleSelector}} BB {RefPtr =^{CSSPrimitiveValueCache}}^{Frame} {OwnPtr =^{CachedResourceLoader}} {RefPtr =^{DocumentPar SER}} B {KURL = {字符串= {RefPtr =^{StringImpl}}} b1b1iiiiiiiiii} {KURL = {字符串= {RefPtr =^{StringImpl}}} b1b1iiiiiiiiii} {KURL = {字符串= {RefPtr =^{StringImpl }}} b1b1iiiiiiiiii} {KURL = {字符串= {RefPtr =^{StringImpl}}} b1b1iiiiiiiiii} {KURL = {字符串= {RefPtr =^{StringImpl}}} b1b1iiiiiiiiii} {字符串= {RefPtr =^{StringImpl}} } {字符串= {RefPtr =^{StringImpl}}} {RefPtr =^{DocumentType}} {OwnPtr =^{的DOMImplementation}} IBIB {RefPtr =^{的CSSStyleSheet}} {RefPtr =^{的CSSStyleSheet}} {RefPtr =^{CSSStyleSheet}} {OwnPtr， 0ul> =^{Vector，0ul>}} BBBBiB {Color = IB} {RefPtr =^{Node}} {RefPtr =^{Node}} {RefPtr =^{Node}} {HashSet，WTF :: HashTraits = {HashTable，WTF :: PtrHash，WTF :: HashTraits，WTF :: HashTraits = ^^ {NodeIterator} iiii}} {HashSet，WTF： ：HashTraits = {HashTable，WTF :: PtrHash，WTF :: HashTraits，WTF :: HashTraits = ^^ {Range} iiii}} S {RefPtr =^{StyleSheetList }} {ListHashSet = {的HashTable ，WTF :: ListHashSetNode，WTF :: IdentityExtractor *>，WTF :: ListHashSetNodeHashFunctions ，WTF :: HashTraits *>，WTF :: HashTraits *> = ^^ {ListHashSetNode} IIII }^{ListHashSetNode}^{ListHashSetNode} {OwnPtr =^{ListHashSetNodeAllocator}}} {ListHashSet = {的HashTable ，WTF :: ListHashSetNode，WTF :: IdentityExtractor *>，WTF :: ListHashSetNodeHashFunctions ，WTF :: HashTraits *>，WTF :: HashTraits *> = ^^ {ListHashSetNode} IIII}^{ListHashSetNode}^{ListHashSetNode} {OwnPtr =^{ListHashSetNodeAllocator}}} {ListHashSet = {的HashTable ，WTF :: ListHashSetNode，WTF :: IdentityExtractor *>，WTF :: ListHashSetNodeHashFunctions ，WTF :: HashTraits *>，WTF :: HashTraits *> = ^^ {ListHashSetNode} iiii}^{ListHashSetNode}^{ListHashSetNode} {OwnPtr =^{ListHashSetNodeAllocator}}} {HashMap中，WebCore的:: FormElementKeyHash，WebCore的:: FormElementKeyHashTraits，WTF :: HashTraits> = {的HashTable ，WTF :: PairFirstExtractor> ，WebCore的:: FormElementKeyHash，WTF :: PairHashTraits> ，WebCore的： ：FormElementKeyHashTraits> =^{pair } iiii}} {Color = IB} {Color = IB} {Color = IB} {String = {RefPtr =^{StringImpl}}} {String = {RefPtr =^{StringImpl}} } {BBiB定時器= ^^？ddiI^{文獻} {？=^q}} BBBBBBBBBBBBBBBBBI {StringWithDirection = {字符串= {RefPtr =^{StringImpl}}} I} {StringWithDirection = {字符串= {RefPtr =^{StringImpl }}} I} B {RefPtr =^{元素}} {OwnPtr =^{RenderArena}}^{AXO bjectCache} {OwnPtr =^{DocumentMarkerController}} {定時器= ^^？ddiI^{文獻} {？=^Q}}^{元素} B {RefPtr =^{SerializedScriptValue}} dBi的{OwnPtr =^{ScriptRunner}} {OwnPtr =^{TransformSource}} {RefPtr =^{文獻}} I {字符串= {RefPtr =^{StringImpl}}} {字符串= {RefPtr =^{StringImpl}}} B {字符串= {RefPtr =^{StringImpl}}}^{渲染對象} {RefPtr =^{TextResourceDecoder}} I {CheckedRadioButtons = {OwnPtr，WTF :: HashTraits， WTF :: HashTraits> =^{HashMap，WTF :: HashTraits，WTF :: HashTraits }}} {FixedArray = [10 {CollectionCache = Q^{Element} IIi {HashMap，WTF： ：WTF :: HashTraits *> = {HashTable，std :: pair *>，WTF :: PairFirstExtractor *> ，WTF :: PtrHash，WTF :: PairHashTraits， WTF :: HashTraits * > ，WTF :: HashTraits =^{pair *>} iiii}} {HashMap，WTF :: PtrHash，WTF :: HashTraits，WTF :: HashTraits *> WTF :: HashTraits * WTF :: HashTraits =^{pair *>} IIII}} BB}]} {FixedArray， WTF :: HashTraits， WTF :: HashTraits ，2UL> = [2 {HashMap中，WTF :: HashTraits，WTF :: HashTraits = {哈希表，WTF :: PairFirstExtractor ，WTF :: PtrHash，WTF :: PairHashTraits， WTF :: HashTraits ，WTF :: HashTraits =^{pair} iiii}}]} {RefPtr =^{XPathEvaluator}} {OwnPtr =^{SVGDocumentExtensions}} {向量= Q {VectorBuffer =^{DashboardRegionValue} Q}} BB {HashMap，WTF :: StringHash，WTF :: HashTraits，WTF :: HashTraits

= {的HashTable ，WTF :: PairFirstExtractor> ，WTF :: StringHash，WTF :: PairHashTraits， WTF :: HashTraits> ，WTF :: HashTraits =^{對 } IIII}} BB [ 1 {IconURL = i {KURL = {String = {RefPtr =^{StringImpl}}} b1b1iiiiiiiiii}}] {HashSet，WTF :: HashTraits = {HashTable，WTF :: PtrHash，WTF :: HashTraits，WTF :: HashTraits HashSet，WTF :: HashTraits = {HashTable，WTF :: PtrHash，WTF :: HashTraits，WTF :: HashTraits = ^^ {Element} iiii}} {HashSet，WTF :: HashTraits = {HashTable，WTF :: PtrHash，WTF :: HashTraits，WTF :: HashTraits = ^^ {Element} iiii}} {HashMap ，WTF :: HashTraits = {哈希表，WTF :: PairFirstExtractor ，WTF :: CaseFoldingHash，WTF :: PairHashTraits， WTF :: HashTraits>，WTF :: HashTraits =^{對} IIII}} {BBBBBBB = RefPtr^{EventQueue}} {RefPtr =^{DocumentWeakReference}} {HashSet，WTF :: HashTraits = {HashTable，WTF :: PtrHash，WTF :: HashTraits，WTF :: HashTraits = ^^ {MediaCanStartListener} iiii}} { QualifiedName的=^{QualifiedNameImpl}} B {RefPtr =^{元素}}^{RenderFullScreen} {定時器= ^^？ddiI^{文獻} {？=^q}} {的Deque，0ul> = {QQ VectorBuffer，0ul> =^{RefPtr} Q}} B {IntRect = {IntPoint = II} {IntSize = II}} {RefPtr =^{RenderStyle}} I {定時器= ^^？ddiI^{文獻} {？=^Q}} {ViewportArguments = FFFFFFF} BB {DocumentTiming = DDDDD} {RefPtr =^{MediaQueryMatcher}} BII {RefPtr =^{ContentSecurityPolicy}}} 16 @ 0：8

Answer 2

您可以使用Objective-C運行功能：

Method class_getClassMethod(Class aClass, SEL aSelector) 
void method_getReturnType(Method method, char *dst, size_t dst_len) 

Objective-C Runtime Reference

首先，獲取方法對象，使用class_getClassMethod

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

然後，詢問使用method_getReturnType返回類型：

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