Objective-C检测一个参数是否可以保留?

我正在运行一个参数列表,但是在这些参数中,值可以是从NSInteger、选择器到NSObjects的任何值。但如果它是NSObject,则需要正确地保留它。我不能简单地检查该类是否与NSObject相同,或者它是否响应retain方法,因为如果在选择器或整数上执行此操作,它就会崩溃。那你怎么还能做到呢?我不知道。

我甚至试着在里面放一个@try@catch,如果没有,就试着保留它可能是一个不需要保留的对象。但它也会立即崩溃:(这里没有错误例外。

object_getClass();

但是当你超过一个NSInteger的时候它就崩溃了。

看看NSInvocation类,你可以调用retainArguments方法,不幸的是,这也会使应用程序崩溃。但是在setArgument的描述中有一点奇怪:

当参数值是一个对象时,传递一个指向要从中复制对象的变量(或内存)的指针

这就意味着有一些东西可以检测出一个参数是否是一个对象,但是如何检测呢?

- (void)addObserver:(NSObject *)observer selector:(SEL)selector arguments:(id)firstObj, ... {
    // Define signature
    NSMethodSignature *signature  = [[observer class] instanceMethodSignatureForSelector:selector];
    NSInvocation      *invocation = [NSInvocation invocationWithMethodSignature:signature];

    // Prepare invocation
    [invocation setTarget:observer];
    [invocation setSelector:selector];

    id        currentObject;
    va_list   argumentsList;
    NSInteger currentIndex = 2;

    if (firstObj) {
        va_start (argumentsList, firstObj);
        while (currentObject = va_arg(argumentsList, id)) {
            [invocation setArgument:&currentObject atIndex:currentIndex];
            currentIndex++;
        }
        va_end(argumentsList);
    }

    // The observer can easily be retained by doing [observer retain];
    // However the arguments may consist of NSIntegers etc. which really don't like
    // to be retained (logically). So I want to skip the argument that don't need
    // retaining.
}

目标

我有一个随机的方法,比如:

- (void)fetchFruitApples:(NSInteger)amount inRange:(NSRange)range withString:(NSString *)aString {
    //Can I fetch fruit? 
    //If so, execute method. 
    //If not wait for a certain event to occur (without blocking the main thread) 
    //Then retry this method with the arguments passed.
    //Thats why here I want to do [MyObject addObserver:self selector:@selector(fetchFruitApples:inRange:withString:) arguments:amount, range, aString, nil];
}