如何在ios中检查（id）对象是否为null？

I have made a function to consume webservices , now I want to check if (id) object is null or not. What I am doing is here:

我已经创建了一个使用webservices的函数，现在我想检查if（id）对象是否为null。我在做什么在这里：

-(void)callService:(NSString*)request param:(NSString*) parameters completion:(void (^)(NSArray *list, NSError *error))completionHandler
{
    [self.manager POST:request parameters:parameters success:^(NSURLSessionDataTask *task, id responseObject) {

        NSLog(@"Response Object: %@", responseObject);

        if (![responseObject isKindOfClass:[NSNull class]]) {

            [self methodUsingJsonFromSuccessBlock:responseObject];

            if (completionHandler) {
                //NSLog(@"%@", list);
                completionHandler(list,nil);
            }
        }
        else {
            NSLog(@"Nothing found");
        }
    }failure:^(NSURLSessionDataTask *task, NSError *error) {

        //NSLog(@"Error: %@", [error description]);
        if (completionHandler) {
            completionHandler(nil,error);
        }
    }];
}

but what I have found on break points is when (id) is null it has NSZeroData but no NSNull so it always passes my condition. I am using AFNetworking

但我在断点上找到的是当（id）为null时它有NSZeroData但没有NSNull所以它总是通过我的条件。我正在使用AFNetworking

Thanks in advance for helping me out.

在此先感谢帮助我。

3 个解决方案

#1

Your responseObject is not NSNull, but an NSData (which _NSZeroData is a subclass of).

您的responseObject不是NSNull，而是NSData（_NSZeroData是其子类）。

So what you really want is this condition:

所以你真正想要的是这种情况：

if ([responseObject isKindOfClass:[NSData class]] && ((NSData *)responseObject).length > 0) {
    // ...
}

#2

This is not the fastest response, but it can be of some use to someone.

这不是最快的响应，但它对某人有用。

Here is what I've been using and what you can do:

以下是我一直在使用的内容以及您可以做的事情：

In some class, say "defaults.h" you can define following:

在某些类中，例如“defaults.h”，您可以定义以下内容：

#define Secure(x) x != (id)[NSNull null] ? x : @""
#define isSecure(x) x != (id) [NSNull null] ? YES : NO

Later, in your method you can use it like this:

稍后，在您的方法中，您可以像这样使用它：

if(isSecure(responseObject)){
    doSuccess
}
else {
    doError
}

First method can be used for example for strings, while the other is general.

第一种方法可以用于例如字符串，而另一种方法是通用的。

#3

try this

尝试这个

put this on top

把它放在首位

#define isNSNull(value) [value isKindOfClass:[NSNull class]]

and then while comparing

然后在比较时

if (isNSNull(object) ...

hope it helps.

希望能帮助到你。