应用程序在使用nsnull计数的循环的第二次运行时崩溃 [英] app is crashing on second run through of loop with nsnull count

问题描述

我有一个循环，在第一次循环中运行良好，但是在第二次循环中我得到了:

I have a loop that works fine the first time through but the second time through the loop I get:

-[NSNull count]: unrecognized selector sent to instance 0x3a094a70
 *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSNull count]: unrecognized selector sent to instance 0x3a094a70'

这是我的代码中崩溃的部分(最后一行):

Here is the part in my code where I know it is crashing (the last line):

...
NSLog(@"dict::%@",dictForPost);
// collect the photo urls in an array
    photosInDict = [NSArray array];

// photos is an array of dictionaries in the dictionary
photosInDict = dictForPost[@"photos"];
    if (photosInDict.count) {
....        

我知道，当photosInDict在dic中没有图片时，它会崩溃，但是我不知道为什么，因为我启动了它上面的数组.

I know that when photosInDict doesnt have pictures in the dic it crashes but I dont get why since I initiated the array above it.

推荐答案

 photosInDict = dictForPost[@"photos"]

替换先前分配并存储在photosInDict中的对象. 因此，之前分配数组没有任何意义.只是

replaces the object previously allocated and stored in photosInDict. Therefore it does not make sense to allocate the array before. Just

NSArray * photosInDict = dictForPost[@"photos"];

然后检查

if ([photosInDict isKindOfClass:[NSArray class]]) {
    // Yes, it is an array. Do something with it.
    if ([photosInDict count]) {
       ...
    }
} 

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