检查Objective-C中从JSON字符串返回的空值 [英] Checking a null value in Objective-C that has been returned from a JSON string

问题描述

我有一个 JSON 对象来自网络服务器。

I have a JSON object that is coming from a webserver.

日志是这样的：

{          
   "status":"success",
   "UserID":15,
   "Name":"John",
   "DisplayName":"John",
   "Surname":"Smith",
   "Email":"email",
   "Telephone":null,
   "FullAccount":"true"
}

注意电话进来了如果用户没有输入，则为null。

Note the Telephone is coming in as null if the user doesn't enter one.

将此值分配给 NSString 时，在 NSLog 它出现为< null>

When assigning this value to a NSString, in the NSLog it's coming out as <null>

I我正在分配这样的字符串：

I am assigning the string like this:

NSString *tel = [jsonDictionary valueForKey:@"Telephone"];

检查此< null> 价值？它阻止我保存 NSDictionary 。

What is the correct way to check this <null> value? It's preventing me from saving a NSDictionary.

我尝试使用条件 [myString长度] 和 myString == nil 和 myString == NULL

此外，iOS文档中哪个地方最适合阅读？

Additionally where is the best place in the iOS documentation to read up on this?

推荐答案

< null> 是NSNull单例记录的方式。所以：

<null> is how the NSNull singleton logs. So:

if (tel == (id)[NSNull null]) {
    // tel is null
}

（单身因素存在，因为你无法添加 nil 到集合类。）

(The singleton exists because you can't add nil to collection classes.)

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