iOS / Objective-C：排除空值

Question

I thought I had seen every possible flavor of values for properties that have not been set in an object, but evidently I have not.

Basically, I want to exclude cases where a value has not been set for a string property of an NSManagedObject . In fact, I want to exclude every case except where there is a valid string of 4 characters or more.

I was using the following code:

if (![contact.pic isKindOfClass:[NSNull class]]&&contact.pic.length>4) {
           //I have a valid string
        }
        else {
            //I don't have valid string
        }

However, it is not excluding some values (most likely where a value was never set) where it logs the values to console as follows:

NSLog(@"contact.pic is: %@",contact.pic); //logs (null)

Can anyone suggest bullet proof code to exclude all but valid strings greater than four characters?

Thanks in advance for any suggestions

Answer 1

It looks like you are not catching the case where the value is nil, have you tried including a catch for this too

if (contact.pic && ![contact.pic isKindOfClass:[NSNull class]] && contact.pic.length >= 4) {
    //I have a valid string
}
else {
    //I don't have valid string
}

Note that I have also made your inequality >= rather than > since your question suggests that 4 is a valid value.

Answer 2

I usually use following three macros in every project for NSString validations as required

#define IfNULL(original, replacement) IsNULL(original) ? replacement : original

#define IsNULL(original) original == (id)[NSNull null] || original == nil

#define IsEmpty(value) (value == (value == nil) || (id)[NSNull null] || ([value isKindOfClass:[NSString class]] && ([value isEqualToString:@""] || [value isEqualToString:@"<null>"] || [value isEqualToString:@"(null)"] || [value isEqualToString:@" "]))) ? YES : NO

Usage

if(!isEmpty(contact.pic)){
    //Do your stuff
}