Objective-C 奇巧淫技--IMS

標籤：swizzling   objective   ios   

奇技淫巧 指過於奇巧而無益的技藝與製品.
IMS指的是 Instance Method Swizzling, 執行個體方法混淆.
下段代碼是一個Instance Method Swizzling和一個Method Swizzling的例子:

// Man.m- (void)run{    NSLog(@"%s, %@", __func__, _name);}- (void)jump{    NSLog(@"%s, %@", __func__, _name);}- (void)handsUp{    NSLog(@"%s, %@", __func__, _name);}- (void)handsDown{    NSLog(@"%s, %@", __func__, _name);}//  ViewController.m- (void)viewDidLoad {    ...    Man *a = [Man manWithName:@"a"];    Man *b = [Man manWithName:@"b"];    [self swizzleInstanceMethodWithInstance:a originalSel:@selector(run) replacementSel:@selector(jump)];    [self swizzleInstanceMethodWithClass:[Man class] originalSel:@selector(handsUp) replacementSel:@selector(handsDown)];    [a run];    [b run];    [a handsUp];    [b handsUp];}// 輸出的結果是2015-03-14 23:53:39.832 testRuntime[2196:629365] -[Man jump], a2015-03-14 23:53:39.833 testRuntime[2196:629365] -[Man run], b2015-03-14 23:53:39.833 testRuntime[2196:629365] -[Man handsDown], a2015-03-14 23:53:39.833 testRuntime[2196:629365] -[Man handsDown], b

為什麼run方法是只有對象a被替換了,handsUp方法是都被替換了呢?
我們先來看下普通的Method Swizzling是如何?的

- (void)swizzleInstanceMethodWithClass:(Class)clazz originalSel:(SEL)original replacementSel:(SEL)replacement{    Method a = class_getInstanceMethod(clazz, original);    Method b = class_getInstanceMethod(clazz, replacement);    // class_addMethod 為該類增加一個新方法    if (class_addMethod(clazz, original, method_getImplementation(b), method_getTypeEncoding(b)))    {        // 替換類方法的實現指標        class_replaceMethod(clazz, replacement, method_getImplementation(a), method_getTypeEncoding(a));    }    else    {        // 交換2個方法的實現指標        method_exchangeImplementations(a, b);    }}

Instance Method Swizzling是用了類似KVO的辦法.
先動態添加一個類MySubclass繼承自原來的類,然後修改對象a的isa為新類,再替換掉新類的方法.

- (void)swizzleInstanceMethodWithInstance:(id)object originalSel:(SEL)original replacementSel:(SEL)replacement{    Class newClass = objc_allocateClassPair([object class], "MySubclass", 0);    objc_registerClassPair(newClass);    Method a = class_getInstanceMethod(newClass, original);    Method b = class_getInstanceMethod([object class], replacement);    if (class_addMethod(newClass, original, method_getImplementation(b), method_getTypeEncoding(b)))    {        class_replaceMethod(newClass, replacement, method_getImplementation(a), method_getTypeEncoding(a));    }    else    {        method_exchangeImplementations(a, b);    }    object_setClass(object, newClass);}

Objective-C 奇巧淫技--IMS