1、错误
先看一个常见的错误
运行一个类没有的实例方法，就会报错‘unrecognized selector sent to instance’
我们知道，Objective-C的方法实际是是消息发送，我们来看一张经典的图
当对象经过查找，一直找不到可以运行的IMP，最后调用
- (void)doesNotRecognizeSelector:(SEL)aSelector
我尝试了去hook这个方法，结果导致
Thread 1: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)
怀疑这个方法是消息调用的失败结果，不能被hook。
所以只好在调用这个方法之前将问题解决
2、解决方案
- 在
methodSignatureForSelector阶段将找不到的Selector添加到NSObject里去， - 在
forwardInvocation阶段将消息重新转发给NSObject
具体代码
- (NSMethodSignature *)ht_methodSignatureForSelector:(SEL)aSelector{
if (![self respondsToSelector:aSelector]) {
_errorSelectorName = NSStringFromSelector(aSelector);
class_addMethod([self class], aSelector, (IMP)dynamicMethodIMP, "v@:");
NSMethodSignature *methodSignature = [self ht_methodSignatureForSelector:aSelector];
return methodSignature;
}else{
return [self ht_methodSignatureForSelector:aSelector];
}
}
- (void)ht_forwardInvocation:(NSInvocation *)anInvocation{
SEL selector = [anInvocation selector];
if ([self respondsToSelector:selector]) {
[anInvocation invokeWithTarget:self];
}else{
[self ht_forwardInvocation:anInvocation];
}
}
其中，dynamicMethodIMP是对应找不到的selector的添加IMP，我们可以再里面实现我们自己的逻辑
#ifdef DEBUG
NSString *error = [NSString stringWithFormat:@"errorClass->:%@\n errorSelector->%@\n errorReason->UnRecognized Selector",NSStringFromClass([self class]),_errorSelectorName];
NSLog(@"%@",error);
#else
//upload error
#endif
}
这样，我们调用不存在的方法就不会报错了
如果，不想对现有的类添加过多的方法，可以用一个专门的类来收集这些方法NSProxy
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector{
if (![self respondsToSelector:aSelector]) {
_errorSelectorName = NSStringFromSelector(aSelector);
class_addMethod([self class], aSelector, (IMP)proxyDynamicMethodIMP, "v@:");
}
NSMethodSignature *methodSignature = [[self class] instanceMethodSignatureForSelector:aSelector];
return methodSignature;
}
- (void)forwardInvocation:(NSInvocation *)anInvocation{
SEL selector = [anInvocation selector];
if ([self respondsToSelector:selector]) {
[anInvocation invokeWithTarget:self];
}else{
[self forwardInvocation:anInvocation];
}
}