NSArray arrayWithObjects: if nil is meant to mark

问题:

If nil is meant to mark the end of parameters, then can I use:

[NSArray arrayWithObjects:obj1, obj2, nil, nil, nil];

as the first nil marks array end and two nils after will be ignored?

I got two opposite answers and will try it out.

update:

The reason why I need to do this, is I need to create an UIAlertView, which may have buttons: 'OK' only, or 'Call' and 'Cancel', so either 'OK' or 'Cancel', is the cancel button, whereas 'Call' is other buttons in one case, in other cases, I do not need any other buttons, that's why I need to do this.

回答1:

The addition of nil to the end is not intended to add nils to an array, its simply an artifact of how C processes ... variable argument lists. It has nothing to do with NSArray or NSMutableArray, you cannot store nil in either.

So whether the compiler accepts, nil, nil, nil is actually irrelevant. The compiler will stop reading at the first nil. And writing that code in the first place shows a misunderstanding of obj C collections and var arg methods.

Why not use the new literal syntax and just say

NSArray *myArray = @[@"bla", @"bla", @"bla"];

Either way the extra nils matter not in the syntax you provided.

回答2:

When you put nil when creating NSArray, objects upto that nil get added. The nil and objects after that are ignored. Just to complete, you can't add nil to NSMutableArray also (say using addObject: method) and doing that will raise exception.

you can put [NSNull null]; though when creating NSArray.

回答3:

Yes, exactly, this can be done. The nils after the first one will be ignored.

回答4:

Why would you intentionally add nil to an array? I think you'd better stop a bit and think twice about why do you have to do this. If you are unsure about the size of the array, you can always go with NSMutableArray.