edwardean / Method-Swizzle-Pitfall

Method-Swizzle-Pitfall

如果UIViewController和一个继承自UIViewController的子类的viewWillAppear:方法都被swizzle，

Code block

+ (void)load {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
Class class = [self class];
SEL originalSelector = @selector(viewWillAppear:);
SEL swizzledSelector = @selector(sub_swizzleviewWillAppear:);
Method originalMethod = class_getInstanceMethod(class, originalSelector);
Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);

IMP originIMP = method_getImplementation(originalMethod);
IMP swizzleIMP = method_getImplementation(swizzledMethod);

BOOL didAddMethod = class_addMethod(class, originalSelector,
method_getImplementation(swizzledMethod),
method_getTypeEncoding(swizzledMethod));
if (didAddMethod) {
class_replaceMethod(class, swizzledSelector,
originIMP,
method_getTypeEncoding(originalMethod));
} else {
method_exchangeImplementations(originalMethod, swizzledMethod);
}
});
}

子类如果没有实现viewWillAppear方法的话在swizzle时会被添加UIViewController的原始方法（注意UIViewController中的viewWillAppear方法并没有call super）, 这时会导致被swizzle之后的父类方法不会被调到。