iOS objc / runtime method_exchangeImplementations

Question

我是在NSMutableArray中做到的：

+load{

        Method fromMethod1 = class_getInstanceMethod(objc_getClass("__NSArrayM"),      @selector(addObject:));
        Method toMethod1 = class_getInstanceMethod(objc_getClass("__NSArrayM"), @selector(ww_addObject:));
        method_exchangeImplementations(fromMethod1, toMethod1);
}


static int number = 0;

-(void)ww_addObject:(id)anObject
{
    NSLog(@"ww_addObject run as :%d times ",number ++);
    if (anObject == nil) {
        return;
    }

    [self ww_addObject:anObject];
}

然后在demo中运行它，像这样记录：

209901] ww_addObject run as :1076 times 
2016-12-22 15:40:00.071 testArr[12062:209901] ww_addObject run as :1077 times 
2016-12-22 15:40:00.071 testArr[12062:209901] ww_addObject run as :1078 times 

为什么它运行1078次???

我的测试代码：

NSMutableArray  *arr = [@[@"11",@"22",@"33"] mutableCopy];
[arr addObject:nil];