如何检查BOOL是否为空？ [英] How to check if a BOOL is null?

问题描述

有没有办法在将值分配给BOOL之前检查一个值是否为NULL / Nil？

Is there a way I can check to see if a value is NULL/Nil before assigning it to a BOOL?

例如，我有一个值NSDictionary可以是TRUE / FALSE / NULL

For example, I have a value in a NSDictionary that can be either TRUE/FALSE/NULL

mySTUser.current_user_following = [[results objectForKey:@"current_user_following"]boolValue];

当值为NULL时，我收到以下错误

When the value is NULL I get the following error

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

我希望能够处理NULL情况。

I would like to be able to handle the NULL case.

推荐答案

你应该检查 [NSNull null] ：

id vUser = [results objectForKey:@"current_user_following"];

if (vUser != [NSNull null]) {
    // do stuff...
}
else {
    // handle the case appropriately...
}

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