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I have the following code in a loop
NSArray * images = [definitionDict objectForKey:@"Images"];
NSLog(@"images in definitionDict %@", images);
if (!images )
NSLog(@"NULL");
else
NSLog(@"NOTNULL");
which gives the following outputs
images in definitionDict (
"/some/brol/brol.jpg"
)
NOTNULL
images in definitionDict <null>
NOTNULL
I do not understand the second case, where the images array is null. Why is this not detected correctly in my test ? How can I debug such a problem ?
409
Nil = (capitalized) is a null pointer to an Objective-C class. NULL = (all caps) is a null pointer to anything else (C pointers, that is). [NSNull null] = (singleton) for situations where use of nil is not possible (adding/receiving nil to/from NSArrays e.g.)
You can check if [string length] == 0 . This will check if it's a valid but empty string (@"") as well as if it's nil, since calling length on nil will also return 0.
A static, plain-text Unicode string object that bridges to String ; use NSString when you need reference semantics or other Foundation-specific behavior.
<null> is not nil. nil will print (null) when printed. What you have is an NSNull. NSNull IS an object, it just doesn't respond to much. Its available as a placeholder for you to use.
To test for NSNull you can use if ([images isEqual:[NSNull null]])
See the docs for more info on NSNull
163
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