先來看看巴博薩是如何封蓋詹姆斯的....腋毛
OK!進入正題，哈哈??
什么是Method Swizzling？
字面上意思：方法調和，也就是方法交換，其中交換的是方法的實現。具體點的來說，我們用
@selector(方法選擇器) 取出來的是一個方法的編號(指向方法的指針) ，用SEL類型表示，它所指向的是一個IMP(方法實現的指針) ，而我們交換的就是這個IMP，從而達到方法實現交換的效果。
有什么作用？
我只能說一下自己的理解，當一個方法在工程中大量被調用時，我們想要批量替換或修改，那就很麻煩，有人說直接修改這個方法的實現，這種方式是不推薦的，因為這會破壞原有方法的完整性，而且也不是所有方法都能被修改，比如閉源，這個時候我們用Method Swizzling就可以很好的處理了。
怎么使用？
首先導入<objc/runtime.h>，其中有一個這樣的API：method_exchangeImplementations(Method m1, Method m2),意思也很明顯就是方法實現交換，我這里貼上兩個封裝好的方法：
/**
交換兩個對象方法的實現
@param srcClass 被替換方法的類
@param srcSel 被替換的方法編號
@param swizzledSel 用于替換的方法編號
*/
- (void)zm_swizzleInstanceMethodWithSrcClass:(Class)srcClass
srcSel:(SEL)srcSel
swizzledSel:(SEL)swizzledSel{
Method srcMethod = class_getInstanceMethod(srcClass, srcSel);
Method swizzledMethod = class_getInstanceMethod([self class], swizzledSel);
if (!srcClass || !srcMethod || !swizzledMethod) return;
//加一層保護措施，如果添加成功，則表示該方法不存在于本類，而是存在于父類中，不能交換父類的方法,否則父類的對象調用該方法會crash；添加失敗則表示本類存在該方法
BOOL addMethod = class_addMethod(srcClass, srcSel, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
if (addMethod)
{
//再將原有的實現替換到swizzledMethod方法上，從而實現方法的交換，并且未影響到父類方法的實現
class_replaceMethod(srcClass, swizzledSel, method_getImplementation(srcMethod), method_getTypeEncoding(srcMethod));
}else
{
method_exchangeImplementations(srcMethod, swizzledMethod);
}
}
/**
交換兩個類方法的實現
@param srcClass 被替換方法的類
@param srcSel 被替換的方法編號
@param swizzledSel 用于替換的方法編號
*/
- (void)zm_swizzleClassMethodWithSrcClass:(Class)srcClass
srcSel:(SEL)srcSel
swizzledSel:(SEL)swizzledSel{
Method srcMethod = class_getClassMethod(srcClass, srcSel);
Method swizzledMethod = class_getClassMethod([self class], swizzledSel);
if (!srcClass || !srcMethod || !swizzledMethod) return;
//注意：類方法是存在于元類中，所以要添加到元類
srcClass = objc_getMetaClass(class_getName(srcClass));
BOOL addMethod = class_addMethod(srcClass, srcSel, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
if (addMethod)
{
class_replaceMethod(srcClass, swizzledSel, method_getImplementation(srcMethod), method_getTypeEncoding(srcMethod));
}else
{
method_exchangeImplementations(srcMethod, swizzledMethod);
}
}
舉幾個栗子
-
友盟統計很多人用過吧，每個控制器頁面出現和消失都要做標記，很煩！所以我們用Method Swizzling對
viewWillAppear&viewWillDisappear跟我們自定義方法交換，然后統一處理@implementation UIViewController (Swizzle) +(void)load{ static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ [self zm_swizzleInstanceMethodWithSrcClass:[self class] srcSel:@selector(viewWillAppear:) swizzledSel:@selector(zm_ViewWillAppear:)]; [self zm_swizzleInstanceMethodWithSrcClass:[self class] srcSel:@selector(viewWillDisappear:) swizzledSel:@selector(zm_ViewWillDisappear:)]; }); } /** 頁面出現的時候會進入到這里實現，即使在子類重寫了ViewWillAppear:方法， 那么在調用[super ViewWillAppear:animated]的時候還是會進入這里。 @param animated 動畫 */ - (void)zm_ViewWillAppear:(BOOL)animated{ //此處調用自己其實就是調用UIViewController的viewWillAppear的原生實現方法。 [self zm_ViewWillAppear:animated]; //統一添加統計代碼 self.title.length == 0?:[MobClick beginLogPageView:self.title]; } - (void)zm_ViewWillDisappear:(BOOL)animated{ [self zm_ViewWillDisappear:animated]; self.title.length == 0?:[MobClick endLogPageView:self.title]; } -
對一些系統原生方法做調換，防止開發過程中因不謹慎導致的crash，比如數組越界、數組和字典插入nil對象、字符串截取越界...，我們都可以在自定義方法中先做判斷，從而過濾掉這些不注意的bug，一勞永逸。這里只對一些常用的方法做處理
不可變數組：
@implementation NSArray (ZMSafe) //數組初始化類 static NSString *KInitArrayClass = @"__NSPlaceholderArray"; //空元素數組類，空數組 static NSString *KEmptyArrayClass = @"__NSArray0"; //單元素數組類，一個元素的數組 static NSString *KSingleArrayClass = @"__NSSingleObjectArrayI"; //多元素數組類，兩個元素以上的數組 static NSString *KMultiArrayClass = @"__NSArrayI"; #define KSelectorFromString(s1,s2) NSSelectorFromString([NSString stringWithFormat:@"%@%@",s1,s2]) +(void)load { static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(KInitArrayClass) srcSel:@selector(initWithObjects:count:) swizzledSel:@selector(zm_safeInitWithObjects:count:)]; [self zm_arrayMethodSwizzleWithRealClass:KEmptyArrayClass prefix:@"zm_emptyArray"]; [self zm_arrayMethodSwizzleWithRealClass:KSingleArrayClass prefix:@"zm_singleArray"]; [self zm_arrayMethodSwizzleWithRealClass:KMultiArrayClass prefix:@"zm_multiArray"]; }); } + (void)zm_arrayMethodSwizzleWithRealClass:(NSString *)realClass prefix:(NSString *)prefix { [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(realClass) srcSel:@selector(objectAtIndex:) swizzledSel:KSelectorFromString(prefix, @"ObjectAtIndex:")]; [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(realClass) srcSel:@selector(arrayByAddingObject:) swizzledSel:KSelectorFromString(prefix, @"ArrayByAddingObject:")]; if (iOS11) { [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(realClass) srcSel:@selector(objectAtIndexedSubscript:) swizzledSel:KSelectorFromString(prefix, @"ObjectAtIndexedSubscript:")]; } } #pragma mark -- swizzled Methods - (instancetype)zm_safeInitWithObjects:(id *)objects count:(NSUInteger)cnt { for (NSUInteger i = 0; i < cnt; i++) { if (!objects[i]) objects[i] = @""; } return [self zm_safeInitWithObjects:objects count:cnt]; } - (id)zm_emptyArrayObjectAtIndex:(NSUInteger)index { if (index >= self.count) return nil; return [self zm_emptyArrayObjectAtIndex:index]; } - (id)zm_singleArrayObjectAtIndex:(NSUInteger)index { if (index >= self.count) return nil; return [self zm_singleArrayObjectAtIndex:index]; } - (id)zm_multiArrayObjectAtIndex:(NSUInteger)index { if (index >= self.count) return nil; // NSLog(@"%@",NSStringFromClass(self.class)); //__NSArrayI // NSLog(@"%@",NSStringFromClass(self.superclass)); //NSArray // __NSArrayI是NSArray的子類 // zm_multiArrayObjectAtIndex:是NSArray的方法,self是__NSArrayI的實例，子類調用父類的方法，沒問題 return [self zm_multiArrayObjectAtIndex:index]; } //解決array[index] 字面量語法超出界限的bug - (id)zm_emptyArrayObjectAtIndexedSubscript:(NSUInteger)index { if (index >= self.count) return nil; return [self zm_emptyArrayObjectAtIndexedSubscript:index]; } - (id)zm_singleArrayObjectAtIndexedSubscript:(NSUInteger)index { if (index >= self.count) return nil; return [self zm_singleArrayObjectAtIndexedSubscript:index]; } - (id)zm_multiArrayObjectAtIndexedSubscript:(NSUInteger)index { if (index >= self.count) return nil; return [self zm_multiArrayObjectAtIndexedSubscript:index]; } - (NSArray*)zm_emptyArrayArrayByAddingObject:(id)anObject { if(!anObject) return self; return [self zm_emptyArrayArrayByAddingObject:anObject]; } - (NSArray*)zm_singleArrayArrayByAddingObject:(id)anObject { if(!anObject) return self; return [self zm_singleArrayArrayByAddingObject:anObject]; } - (NSArray*)zm_multiArrayArrayByAddingObject:(id)anObject { if(!anObject) return self; return [self zm_multiArrayArrayByAddingObject:anObject]; }可變數組：
這里使用MRC寫法，是為了修復[UIKeyboardLayoutStar release]: message sent to deallocated instance的Bug，所以該文件需要添加ARC支持-fno-objc-arc
@implementation NSMutableArray (ZMSafe)
static NSString *KMArrayClass = @"__NSArrayM";+(void)load{ static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ @autoreleasepool { [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(KMArrayClass) srcSel:@selector(addObject:) swizzledSel:@selector(zm_safeAddObject:)]; [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(KMArrayClass) srcSel:@selector(insertObject:atIndex:) swizzledSel:@selector(zm_safeInsertObject:atIndex:)]; [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(KMArrayClass) srcSel:@selector(removeObjectAtIndex:) swizzledSel:@selector(zm_safeRemoveObjectAtIndex:)]; [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(KMArrayClass) srcSel:@selector(replaceObjectAtIndex:withObject:) swizzledSel:@selector(zm_safeReplaceObjectAtIndex:withObject:)]; [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(KMArrayClass) srcSel:@selector(objectAtIndex:) swizzledSel:@selector(zm_safeObjectAtIndex:)]; if (iOS11) { [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(KMArrayClass) srcSel:@selector(objectAtIndexedSubscript:) swizzledSel:@selector(zm_safeObjectAtIndexedSubscript:)]; } }); } - (void)zm_safeAddObject:(id)anObject{ @autoreleasepool { if(!anObject)return; [self zm_safeAddObject:anObject]; } } - (void)zm_safeInsertObject:(id)anObject atIndex:(NSUInteger)index{ @autoreleasepool { if(!anObject || index > self.count)return; [self zm_safeInsertObject:anObject atIndex:index]; } } - (void)zm_safeRemoveObjectAtIndex:(NSUInteger)index{ @autoreleasepool { if(index >= self.count) return; [self zm_safeRemoveObjectAtIndex:index]; } } - (void)zm_safeReplaceObjectAtIndex:(NSUInteger)index withObject:(id)anObject{ @autoreleasepool { if(index >= self.count || !anObject) return; [self zm_safeReplaceObjectAtIndex:index withObject:anObject]; } } - (id)zm_safeObjectAtIndex:(NSUInteger)index{ @autoreleasepool { if (index >= self.count) return nil; return [self zm_safeObjectAtIndex:index]; } } - (id)zm_safeObjectAtIndexedSubscript:(NSUInteger)index{ @autoreleasepool { if (index >= self.count) return nil; return [self zm_safeObjectAtIndexedSubscript:index]; } }不可變字典：
@implementation NSDictionary (ZMSafe) static NSString *KDictionaryClass = @"__NSPlaceholderDictionary"; +(void)load{ static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(KDictionaryClass) srcSel:@selector(initWithObjects:forKeys:count:) swizzledSel:@selector(zm_safeInitWithObjects:forKeys:count:)]; }); } - (instancetype)zm_safeInitWithObjects:(id*)objects forKeys:(id*)keys count: (NSUInteger)cnt{ for (NSUInteger i = 0; i < cnt; i++) { if(!keys[i]) keys[i] = @""; if(!objects[i]) objects[i] = @""; } return [self zm_safeInitWithObjects:objects forKeys:keys count:cnt]; }可變字典:
@implementation NSMutableDictionary (ZMSafe) static NSString *KMDictionaryClass = @"__NSDictionaryM"; +(void)load{ static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(KMDictionaryClass) srcSel:@selector(setObject:forKey:) swizzledSel:@selector(zm_safeSetObject:forKey:)]; }); } - (void)zm_safeSetObject:(id)anObject forKey:(id <NSCopying>)aKey{ if(!anObject || !aKey) return; [self zm_safeSetObject:anObject forKey:aKey]; }不可變字符串:
@implementation NSString (ZMSafe) static NSString *KStringClass = @"__NSCFString"; +(void)load{ static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(KStringClass) srcSel:@selector(characterAtIndex:) swizzledSel:@selector(zm_safeCharacterAtIndex:)]; [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(KStringClass) srcSel:@selector(substringWithRange:) swizzledSel:@selector(zm_safeSubstringWithRange:)]; [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(KStringClass) srcSel:@selector(substringFromIndex:) swizzledSel:@selector(zm_safeSubstringFromIndex:)]; [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(KStringClass) srcSel:@selector(substringToIndex:) swizzledSel:@selector(zm_safeSubstringToIndex:)]; [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(KStringClass) srcSel:@selector(rangeOfString:) swizzledSel:@selector(zm_safeRangeOfString:)]; }); } - (unichar)zm_safeCharacterAtIndex:(NSUInteger)index{ if(index >= self.length) return 0; return [self zm_safeCharacterAtIndex:index]; } - (NSString *)zm_safeSubstringFromIndex:(NSUInteger)from{ if(from > self.length) return @""; return [self zm_safeSubstringFromIndex:from]; } - (NSString *)zm_safeSubstringToIndex:(NSUInteger)to{ if(to > self.length) return self; return [self zm_safeSubstringToIndex:to]; } - (NSString *)zm_safeSubstringWithRange:(NSRange)range{ if(range.location + range.length > self.length) return @""; return [self zm_safeSubstringWithRange:range]; } - (NSRange)zm_safeRangeOfString:(NSString *)searchString{ if(!searchString) return NSMakeRange(0, 0); return [self zm_safeRangeOfString:searchString]; }可變字符串:
@implementation NSMutableString (ZMSafe) static NSString *KMStringClass = @"__NSCFConstantString"; +(void)load{ static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(KMStringClass) srcSel:@selector(replaceCharactersInRange:withString:) swizzledSel:@selector(zm_safeReplaceCharactersInRange:withString:)]; [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(KMStringClass) srcSel:@selector(insertString:atIndex:) swizzledSel:@selector(zm_safeInsertString:atIndex:)]; [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(KMStringClass) srcSel:@selector(deleteCharactersInRange:) swizzledSel:@selector(zm_safeDeleteCharactersInRange:)]; [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(KMStringClass) srcSel:@selector(appendString:) swizzledSel:@selector(zm_safeAppendString:)]; [self zm_swizzleInstanceMethodWithSrcClass:NSClassFromString(KMStringClass) srcSel:@selector(setString:) swizzledSel:@selector(zm_safeSetString:)]; }); } - (void)zm_safeReplaceCharactersInRange:(NSRange)range withString:(NSString *)aString{ if(range.location + range.length > self.length || !aString) return; [self zm_safeReplaceCharactersInRange:range withString:aString]; } - (void)zm_safeInsertString:(NSString *)aString atIndex:(NSUInteger)loc{ if (!aString || loc > self.length) return; [self zm_safeInsertString:aString atIndex:loc]; } - (void)zm_safeDeleteCharactersInRange:(NSRange)range{ if(range.location + range.length > self.length) return; [self zm_safeDeleteCharactersInRange:range]; } - (void)zm_safeAppendString:(NSString *)aString{ if(!aString) return; [self zm_safeAppendString:aString]; } - (void)zm_safeSetString:(NSString *)aString{ if(!aString) return; [self zm_safeSetString:aString]; } 就列這些吧，后續想到了在加，更多的是提供一種思路，開發中可以靈活運用，但是也不能亂用，不然會出現意想不到的后果??
注意幾點
- 最好在
+(load)方法中來調用，因為+(load)能確保一定被調用，而且調用時機非常早，在裝載類文件時就會被調用（程序啟動前），所以在運行時你的Method Swizzling一定是執行了的。 - 在執行Method Swizzling的時候最好加上
dispatch_once，雖然說+(load)只會被系統調用一次，但是如果在子類或子類的子類調用了[super load]，那么父類會再次調用，導致Method Swizzling多次執行，換來換去，到時候有沒有調換過來就看運氣了，那就尷尬了?? - 如果交換的是系統原生方法，一定要在自定義實現方法中調用自身方法，也就是原生實現方法，因為我們不是要整個重寫原生實現方法，而是在它基礎之上添加我們自己的東西；如果交換的是自定義方法，那就看需求而定咯??
