我正在尝试实现 isa swizzling，因为我需要在某些对象的 dealloc 方法中发生一些操作。我正在覆盖 - (Class)class; 返回原始类的方法（如 KVO 所做的那样）。一切正常，直到我尝试将观察者添加到 swizzled 对象。它只是崩溃。
- 0x00000000 在 0x00000000 ()
- _NSKeyValueRetainedObservationInfoForObject()中的0x0091d22a
- 0x0092ec88 在 -[NSObject(NSKeyValueObserverRegistration) _addObserver:forProperty:options:context:] ()
- 0x0092d6fd 在 -[NSObject(NSKeyValueObserverRegistration) addObserver:forKeyPath:options:context:] ()
这是混合的实现
- (void)swizzleClass
{
NSString *proxyClassName = [NSString stringWithFormat:@"MDSwizzled_%@", NSStringFromClass(self->isa)];
Class proxyClass = NSClassFromString(proxyClassName);
if (!proxyClass)
proxyClass = [self createProxyClassWithName:proxyClassName];
object_setClass(self, proxyClass);
}
- (Class)createProxyClassWithName:(NSString *)proxyClassName
{
const char *c_proxyClassName = [proxyClassName cStringUsingEncoding:NSUTF8StringEncoding];
Class proxyClass = objc_allocateClassPair(self->isa, c_proxyClassName, 0);
Class dummyClass = [MDDummy class];
class_addMethodFromClass(proxyClass, dummyClass, @selector(dealloc));
class_addMethodFromClass(proxyClass, dummyClass, @selector(class));
objc_registerClassPair(proxyClass);
return proxyClass;
}
MDDummy 它只是一个以 convinietn 方式保存的类方法（这与添加原始函数没有区别）。
@implementation MDDummy
- (void)dealloc
{
//Special thinngs
[super dealloc];
}
- (Class)class
{
return //original class;
}
@end
编辑：
下面是 class_addMethodFromClass 函数的实现：
void class_addMethodFromClass(Class class, Class sourceClass, SEL selector)
{
Method method = class_getInstanceMethod(sourceClass, selector);
IMP methodImplementation = method_getImplementation(method);
const char *types = method_getTypeEncoding(method);
class_addMethod(class, selector, methodImplementation, types);
}