从JSON数据为NSString分配null时发生崩溃

I am experiencing a crash that I have narrowed down to this line of code but I dont understand how I can avoid it.

我遇到了崩溃，我已经缩小到这行代码，但我不明白我怎么能避免它。

NSString *variantImageUrl = variantEdge[@"node"][@"image"][@"src"];

If the value of src is null the app crashes with the following error message

如果src的值为null，则应用程序崩溃并显示以下错误消息

    2017-11-21 17:23:27.023988+0800 NWMPos[3218:2124447] -[NSNull objectForKeyedSubscript:]: unrecognized selector sent to instance 0x1b2a01650
2017-11-21 17:23:27.026199+0800 NWMPos[3218:2124447] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSNull objectForKeyedSubscript:]: unrecognized selector sent to instance 0x1b2a01650'

As long as the value of src is a proper string it works fine

只要src的值是一个合适的字符串，它就可以正常工作

But I cannot check the value for null before I assign it so how can avoid the crash?

但是在分配之前我无法检查null的值，那么如何避免崩溃呢？

2 个解决方案

#1

Add check for null:

添加检查null：

if(![variantEdge[@"node"][@"image"][@"src"] isEqual:[NSNull null]])
{
    NSString *variantImageUrl = variantEdge[@"node"][@"image"][@"src"];
}

#2

Clumsy as hell, but

笨拙地说，但是

NSDictionary *dict = variantEdge;

for (NSString *key in @[@"node", @"image"]) {
   dict = dict[key];
   if (![dict isKindOfClass:NSDictionary.class]) {
      dict = nil;
      break;
   }
}

NSString *url = dict ? dict["src"] : nil;

#1