Add NSMutableArray to another NSMutableArray

Question

Hey! I've been trying to add an array to an NSMutableArray using the addObject syntax. The app crashes without any explicit mention of an error. Could you please tell me how this is done?

I have a class Stack that creates an array. So I call that class using an instance called tem that I have created. Hence, [self tem] is my call to the array. Through the program I merely add UILabels to the array(I know you'd suggest adding a string and then changing to UILabels, but I need to do it this way) and towards the end, I'd like to add this array to my 'list' array.

-(Stack *)tem {
  if(!tem)
    tem=[[Stack alloc]init];
  return tem;
}

-(void)viewDidLoad{
  //code
  list=[NSMutableArray arrayWithArray:[self list].array];
}

-(IBAction)opPr:(UIButton *)sender
{
  if([[[sender titleLabel]text] compare: @"="]==0) {
    //code
    UILabel *t=[[UILabel alloc]init];
    //complete creating label
    [[self tem]push:t];
    //add above label to tem array
    [list addObject:[self tem].array];
    [table reloadData];
  }
}

Share some code of yours

Oleg Danu
– Oleg Danu

2011-01-20 07:16:54 +00:00
Commented Jan 20, 2011 at 7:16 — Oleg Danu
– Oleg Danu, Commented Jan 20, 2011 at 7:16

Ryan Ballantyne · Accepted Answer · 2011-01-20 08:47:15Z

3

OK, this answer got all cluttered with edits. I've edited it to be more clear, at the possible expense of understanding the thread of how we arrived at the final answer.

The final answer

The answer was to change:

list=[NSMutableArray arrayWithArray:[self list].array];

To:

list = [[NSMutableArray alloc] init];

(...Which isn't really the best way to create an NSMutableArray, but it may work anyway.)

This was based on an erroneous version of the asker's code

Based on your comment that it crashes after [list addObject:[self tem].array];, I must conclude that your instance variable list is of type Stack*, and that Stack is not a subclass of NSMutableArray. If so, that's your issue.

In that case, changing that line to [[list array] addObject:[self tem].array]; should fix it.

This is just good advice

As an aside, NSMutable array is perfectly capable of acting as a stack without modification. Example:

NSMutableArray* ar = [NSMutableArray arrayWithCapacity:someCapacity];
// Push
[ar addObject:narf]; // narf being some object reference
// Pop
id popped = [ar lastObject];
[ar removeLastObject];

If you want to encapsulate stack behavior in a semantically consistent way, you can add push and pop methods to NSMutableArray using a category. This would make your code simpler and less prone to error.

This was my first stab at answering the question, before any code had been posted

This is a stab in the dark since you've not posted any code. BUT. One way to accomplish that with arrays is by creating arrays using [NSArray arrayWithObjects:obj obj ... nil] and omitting the nil terminator on the list of objects. Are you by any chance doing that?

edited Jan 20, 2011 at 8:47

answered Jan 20, 2011 at 7:27

Ryan Ballantyne

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13 Comments

Label Over a year ago

Okay before I post code, here's a small brief. I have a class Stack that creates an array. So I call that class using an instance called tem that I have created. Hence, [self tem] is my call to the array. Through the program I merely add UILabels to the array(I know you'd suggest adding a string and then changing to UILabels, but I need to do it this way) and towards the end, I'd like to add this array to my 'list' array. -(Stack *)list { if(!list) list=[[Stack alloc]init]; return list; }

Label Over a year ago

I'm sorry, I have edited the code. There was a small error. I've posted the corrected code in italics (it appears within asterisks)

Label Over a year ago

Please take a look at the edited code. The first method has been changed. It might help clear things up about Stack and Array. For clarification: tem: instance of class Stack that creates an NSMutableArray. list: NSMutableArray created in current class.

Ryan Ballantyne Over a year ago

In viewDidLoad, this line is suspect: list=[NSMutableArray arrayWithArray:[self list].array]; I'm actually surprised it doesn't crash then and there, since list should be uninitialized at that point. Or is that another mistake?

Ryan Ballantyne Over a year ago

That would be best asked in a new question, instead of in the comments thread on this one. Also, if you feel I've answered your original question, around here it's considered good form to mark my answer as accepted. :)

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