How do I check if an object exists at a certain index of an NSMutableArray?

问题

For instance, how could I verify if there is an item at the index 3?

The objects in the NSArray are instantiated from the class "Animal."

回答1:

Well, since NSMutableArray has to hold non-nil objects, as long as the array is big enough, you know there's something at index i:

if ([myArray count] > 3) {
    id myObj = [myArray objectAtIndex:3];
    ...
}

If you needed to check something elsek, like say make sure it didn't have a reference to the NSNull singleton, you could then check

if (myObj != [NSNull null]) ...

回答2:

Since there can be no 'gaps' in a NSMutableArray's storage, if your index is less than [array count], you can be certain an object is present at that index.

回答3:

try this code

for(int j = 0; j < [yourArray count]; j++)
{
    if(obj isKindOfClass:[Animal class]]) {
        return
    }
}

来源：https://stackoverflow.com/questions/10117543/how-do-i-check-if-an-object-exists-at-a-certain-index-of-an-nsmutablearray