iOS Add content form a UITextfield to an NSMutableArray everytime a button is clicked

fstigre · Nov 16, 2012

Hi,

I will start by saying what I need to acomplish. I have a button and a UITextfield, what I want to happen is...

1- Every time the button is clicked, whatever it is in the textfield to be put in an NSMutableArray (only numbers).
2- Display each item in the array to the screen (in a UILabel), each in a separate line.
3- Display the sum of all items in the array in a different UILabel.

My problem is getting the values from the textfield and appending them to the array.

The following code does exactly what I need BUT the values are NOT coming from a textfield, they are individual NSNumbers.

Code:

- (IBAction)addText:(id)sender { 
    
    NSNumber *myInt;
    myInt = [NSNumber numberWithInt:5];
    NSNumber *myInt2;
    myInt2 = [NSNumber numberWithInt:10];
    NSNumber *myInt3;
    myInt3 = [NSNumber numberWithInt:20];        
        
    NSMutableArray *numbers =  [NSMutableArray arrayWithObjects: myInt, myInt2, myInt3,nil];   
    
    int result =0;    
    NSString *string = @"";    
    
    for(int i = 0; i < [numbers count]; i++)    {
        
        int nums = [[numbers objectAtIndex:i] intValue];        
        self.display.numberOfLines=0;
        string = [string stringByAppendingFormat:@"Item: %i \n", nums];
        
        result += [[numbers objectAtIndex:i] intValue];
    }
        
    self.display.text = string;   
    self.total.text = [NSString stringWithFormat:@"Total: %i", result];    
    
}

I tried the following code but it only outputs whatever is in the textfield at the time of the execution, it doesn't retain previous values. I tried declaring the array and the textfield outside the method (addText) thinking that it was because of the life sycle of the method but it didn't work.

Code:

- (IBAction)addText:(id)sender { 
  
    NSNumber *myInt =[NSDecimalNumber decimalNumberWithString:self.inputText.text];       
    NSMutableArray *numbers =  [NSMutableArray arrayWithObjects: nil];
    
    [numbers addObject:myInt];  
    
    int result =0;       
    NSString *string = @"";    
    
    for(int i = 0; i < [numbers count]; i++)    {
        
        int nums = [[numbers objectAtIndex:i] intValue];        
        self.display.numberOfLines=0;
        string = [string stringByAppendingFormat:@"Item: %i \n", nums];
        
        result += [[numbers objectAtIndex:i] intValue];
    }
        
    self.display.text = string;   
    self.total.text = [NSString stringWithFormat:@"Total: %i", result];    
    
}

Any idea what am I doing wrong?

Thanks a lot.

dejo · Nov 16, 2012

fstigre said:
I tried declaring the array and the textfield outside the method (addText) thinking that it was because of the life sycle of the method but it didn't work

Didn't work how? Did you get run-time or compile-time errors? More details please. Show your code for this as well.

Basically, your issue boils down to scope. You want your array to live longer than a single execution of a method. I think an instance variable in your viewController would work if you don't want your array to have scope outside of that viewController. If you do need it to have wider scope, you'll need consider other data-persistence approaches.

fstigre · Nov 16, 2012

dejo said:
Didn't work how? Did you get run-time or compile-time errors? More details please. Show your code for this as well.

Basically, your issue boils down to scope. You want your array to live longer than a single execution of a method. I think an instance variable in your viewController would work if you don't want your array to have scope outside of that viewController. If you do need it to have wider scope, you'll need consider other data-persistence approaches.

No, I didn't get any compile errors, it just didn't make a difference, it worked but it didn't retain previous values it only showed the last value.

I will play around with the scope of my array as you suggested, I just needed to know if I was on the right track which it looks like I'm, I just need to play around more.

Thanks a lot for your help.

dejo · Nov 16, 2012

Be sure your code is not running this line in addText:

Code:

NSMutableArray *numbers =  [NSMutableArray arrayWithObjects: nil];

Do you know why?

fstigre · Nov 16, 2012

No, can you please explain why?

and to be quite honest I didn't understand your statement either.

Be sure your code is not running this line in addText:

dejo · Nov 16, 2012

Hmm, if you don't know what that line of code does, why do you have it in your code?

How comfortable are you with the fundamentals of Objective-C programming? If not much, I suggest you step away from the real coding and take the time to learn them before you return to tackle this issue.

fstigre · Nov 16, 2012

I didn't know what were you referring to with "addText", but I just realized that it is how I called my method. Sorry for the miss understanding, this is code I'm using for practicing purposes and I didn't put too much attention to how I named the method, my bad.

I now know exactly what you meant with that statement, sorry.

dejo · Nov 16, 2012

Alright. So, can you now explain why you don't want this in your addText:?

Code:

numbers =  [NSMutableArray arrayWithObjects: nil];

fstigre · Nov 16, 2012

I believe, it is because of the life cycle of the method, the array will basically die when the method finish its execution.

I hope I got that right.

dejo · Nov 16, 2012

fstigre said:
I believe, it is because of the life cycle of the method, the array will basically die when the method finish its execution.

If you make numbers a local variable within your addText: method, correct.

But, I'm asking about something else, to make sure you understand it correctly.
So, let's say you now have

NSMutableArray *numbers;

as an instance variable of your class.
Do you still want:

Code:

numbers =  [NSMutableArray arrayWithObjects:nil];

in your addText: method? If not, why not? If so, why so?

fstigre · Nov 16, 2012

This is what I did which worked.

Declared my NSMutableArray in my header file like so...

@interface ViewController : UIViewController
{
NSMutableArray *numbers;
}
...
@end

... then I defined it in the viewDidLoad method.

- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
numbers = [NSMutableArray arrayWithObjects: nil];
}

but left ...

[numbers addObject:myInt];

in the addText method because this will add the numbers every time the method is called.

I hope this answers part of you questions.

Thanks a lot for trying hard to make me understand these basic and important programming concepts.

dejo · Nov 16, 2012

fstigre said:
I hope this answers part of you questions.

It does. Thanks.

Just a clarification, though. When you said you "defined it in the viewDidLoad", that's not exactly the case, at least to me. You defined/declared numbers in your header file. What you are doing in viewDidLoad is assign it a value, which happens to be an empty array. What you coded is equivalent to a common alloc-init, so I would word what you did there as "initializing" the value (which you need to do in order to add objects to it). And you could also have just initialized it with:

Code:

numbers = [[NSMutableArray alloc] init];

or even:

Code:

numbers = [NSMutableArray array];

fstigre · Nov 16, 2012

Thanks a lot for your help!

You are awesome!

ArtOfWarfare · Nov 17, 2012

fstigre said:
Thanks a lot for your help!

You are awesome!

Mark the topic as resolved. (Go to your first post, click edit, go advanced, and click on the spinner to the left of the topic title and pick resolved.)

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iOS Add content form a UITextfield to an NSMutableArray everytime a button is clicked

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