hook实例函数与类函数的不一样点。

1、hook实例函数

这个是咱们比较常见的，执行以后，test1函数就指向hooktest1了

Class originalClass = objc_getClass("ViewControllerA");
    SEL originalSelector = @selector(test1);
    SEL swizzledSelector = @selector(hooktest1);
    
    // 若originalClass已经存在test1方法，则返回NO
    Method originalMethod = class_getInstanceMethod(originalClass, originalSelector);
    Method swizzledMethod = class_getInstanceMethod(originalClass, swizzledSelector);
    BOOL didAddMethod = class_addMethod(originalClass,originalSelector,method_getImplementation(swizzledMethod),method_getTypeEncoding(swizzledMethod));
    
    // 若原来的方法并不存在，则添加便可
    if (didAddMethod) {
        class_replaceMethod(originalClass,swizzledSelector,method_getImplementation(originalMethod),method_getTypeEncoding(originalMethod));
    }
    method_exchangeImplementations(originalMethod, swizzledMethod);

有一个问题，上面的作法是hook这个类的A函数指向B函数，如何hook这个类的A函数指向另外一个类的B函数呢？代码修改以下

Class originalClass = objc_getClass("ViewControllerA");
    Class swizzledClass = objc_getClass("ViewControllerB");
    SEL originalSelector = @selector(test1);
    SEL swizzledSelector = @selector(hooktest1);
    
    // 若originalClass已经存在test1方法，则返回NO
    Method originalMethod = class_getInstanceMethod(originalClass, originalSelector);
    Method swizzledMethod = class_getInstanceMethod(swizzledClass, swizzledSelector);
    BOOL didAddMethod = class_addMethod(swizzledClass,originalSelector,method_getImplementation(swizzledMethod),method_getTypeEncoding(swizzledMethod));
    
    // 若原来的方法并不存在，则添加便可
    if (didAddMethod) {
        class_replaceMethod(originalClass,swizzledSelector,method_getImplementation(originalMethod),method_getTypeEncoding(originalMethod));
    }
    method_exchangeImplementations(originalMethod, swizzledMethod);

2、hook类函数

实例函数和类函数，主要不一样点在于class_getInstanceMethod和class_getClassMethod，下面是hook类函数的写法。

Class originalClass = objc_getClass("ViewControllerA");
    Class swizzledClass = objc_getClass("ViewControllerB");
    SEL originalSelector = @selector(test2);
    SEL swizzledSelector = @selector(hooktest2);
    
    // 若originalClass已经存在test2方法，则返回NO
    Method originalMethod = class_getClassMethod(originalClass, originalSelector);
    Method swizzledMethod = class_getClassMethod(swizzledClass, swizzledSelector);
    BOOL didAddMethod = class_addMethod(swizzledClass,originalSelector,method_getImplementation(swizzledMethod),method_getTypeEncoding(swizzledMethod));
    
    // 若原来的方法并不存在，则添加便可
    if (didAddMethod) {
        class_replaceMethod(originalClass,swizzledSelector,method_getImplementation(originalMethod),method_getTypeEncoding(originalMethod));
    }
    method_exchangeImplementations(originalMethod, swizzledMethod);

还有一个不一样点，就是在不一样类的状况下，hook以后的函数，若是要调用原函数，实例函数的，只须要以下

- (void)hooktest1 {
    [self hooktest1];
}

可是，hook以后的类函数，须要这样调用原函数

+ (void)hooktest2 {
    [objc_getClass("ViewControllerB") hooktest2];
}

基本上就这些了，用的好就很方便了。