how to add nil to nsmutablearray?

Question

NSArray *array = [[NSArray alloc] initWithObjects:@"ΕΛΤΑ",
                      @"ΕΛΤΑ COURIER", @"ACS", @"ACS ΕΞΩΤΕΡΙΚΟ", 
                      @"DHL", @"INTERATTICA", @"SPEEDEX", 
                      @"UPS", @"ΓΕΝΙΚΗ ΤΑΧΥΔΡΟΜΙΚΗ", @"ΜΕΤΑΦΟΡΙΚΕΣ ΕΞΩΤΕΡΙΚΟΥ", nil];

This is working because it has nil at the end.

But I add objects like this: addObject:name etc... So at the end I have to add nil I do this addObhect:nil but when I run the app it still crashes at cellForRowAtIndexPath:

how can I do this work?

Ok, I dont have to add nil

What is the reason that my app crashes then?

Solution 1

You can't add nil when you're calling addObject.

Solution 2

If you must add a nil object to a collection, use the NSNull class:

The NSNull class defines a singleton object used to represent null values in collection objects (which don’t allow nil values).

Assuming "array" is of type NSMutableArray:

....
[array addObject:[NSNumber numberWithInt:2];
[array addObject:@"string"];
[array addObject:[NSNull null]];

Solution 3

You don't need to call [addObject:nil]

The nil in initWithObjects: is only there to tell the method where the list ends, because of how C varargs work. When you add objects one-by-one with addObject: you don't need to add a nil.

Solution 4

If you really want a Null-ish item in your collection, NSNull is there for that.

Solution 5

You need to add NSNull class and the best way to do it is like this:

NSArray *array = @[ @"string", @42, [NSNull null] ];

I personally recommend to use a specific value like 0 instead of null or nil in your design of your code, but sometimes you need to add null.

There is a good explanation from this Apple reference.

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Comments

[Nimrod]

Also, the nil is called a "sentinel" because it "guards" the end of the list so that things don't iterate off of the end. It's worth knowing that it's called a sentinel because you may see a compiler error/warning like "missing sentinel value ...". In this case it means you forgot a nil at the end of something, usually a list after initWithObjects.

[Supertecnoboff]

So basically if you are add using the addObjects method on a NSMutableArray, you don't need to add a nil at the end? It just knows when it reaches the end itself?

[tmr]

for new folks (me), example of test to see if array element equals the inserted nil value, 'if ([self.voice objectAtIndex:indexPath.row] != [NSNull null]) {' (thank you akosma)