How to create a dynamic array that keeps its size in objective c?

Question

I'm writing an iOS program in objective c and I need an array with the following characteristics:

1) It's shape needs to be decided at runtime.

2) It needs to be able to be stored as a property or a global inside an objective-c class

3) When I insert an object at a specific index it needs to stay at that index. For instance, if I insert at index 5, the object needs to overwrite whatever is at index 5 and do no shifting of this element or any other elements (Similar to how a java array works)

I've looked at NSMutableArray but that doesn't seem to fit what I'm describing above because it shifts elements as you insert. I've also tried NSString *myArray = malloc(10 * sizeof(NSString *)); but this gives me an error regarding requiring a bridged cast. And I don't know what that is.

I'm using ARC, in case that matters.

Jason Kulatunga · Accepted Answer · 2012-06-07 14:45:08Z

8

1) nameOfMyArray = [[NSMutableArray alloc] initWithObjects:@"obj1", @"obj2", "obj3",nil];

3) Instead of doing an insert operation, why not just do a replace operation?

[nameOfMyArray replaceObjectAtIndex:0 withObject: @"newObject here"];

edited Jun 7, 2012 at 14:45

answered Jun 7, 2012 at 14:32

Jason Kulatunga

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5 Comments

UIAdam Over a year ago

He could also fill the array with NSNulls if he knows the size but not the contents initially.

Matt K Over a year ago

Note: You'd would have to check array bounds first and add a bunch of nils if the array isn't big enough.

Christian Over a year ago

Update your code to say initWithObjects:@"obj1", @"obj2", @"obj3", nil]; You are missing a nil at the end, and use the correct code for initialization.

Christian Over a year ago

@mkb you can't add nil to a collection. You'd need to add [NSNull null]

Jason Kulatunga Over a year ago

@Christian thanks for the comment, I completely forgot about the nil termination, too tired

Christian · Accepted Answer · 2012-06-07 14:33:14Z

3

Sounds like you want typical NSMutableArray behavior.

NSMutableArray *arr = [[NSMutableArray alloc] init];
// add a few objects, let's assume there are 10 objects
[arr replaceObjectAtIndex:5 withObject:myObject];

Using the replace method, nothing will be shifted. Your code seems more C-like, and not Objective-C like. I'd recommend reading a book or some documentation to understand how Objective-C objects are supposed to be used -- you'll never malloc an Objective-C object, instead you should be using the alloc class method.

answered Jun 7, 2012 at 14:33

Christian

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