Objective C variable accessible by multiple methods

Question

This is my second day programming in ObjectiveC so I apologize for the noob question.

I have a ViewController that does an API call using async and asihttprequest:

@synthesize loadingStatus;
- (void)loadStatsData
{
    [indicator setHidden:NO];

    loadingStatus = [NSDictionary dictionaryWithObjects:[NSArray arrayWithObjects:@"bad", nil] forKeys:[NSArray arrayWithObjects:@"amount", nil ] ];

    [RESTApiController request:@"/method.json" method:@"GET" options:[NSDictionary dictionaryWithObjects:[NSArray arrayWithObject:@"amount"] forKeys:[NSArray arrayWithObject:@"receiving"] ] parent:self];
}

and receiving it like this:

- (void)requestFinished:(ASIHTTPRequest *)request
{
    if (receiving == @"amount")
    {
      // do stuff
      [loadingStatus setValue:@"good" forKey:@"amount"];
    }

    if ([loadingStatus valueForKey:@"amount"] == @"good"]) 
      [indicator setHidden:YES];
}

The app crashes when it tries to use the loadingStatus variable in requestFinished(). I guess somehow the variable gets dellocated, but I'm unsure as how to approach this.

Two questions: 1) How can I keep loadingStatus's state across methods calls so I can use it in the way I wrote the code 2) Is there a better way of achieving my goal of checking if API calls are completed and hiding the ActivityIndicator?

-M.

Rayfleck · Accepted Answer · 2011-05-10 23:16:28Z

3

Do it this way: refer to loadingStatus as self.loadingStatus

self.loadingStatus = [NSDictionary dictionaryWithObjects:[NSArray arrayWithObjects:@"bad", nil] forKeys:[NSArray arrayWithObjects:@"amount", nil ] ];

That way, it goes through the accessor, and does a retain on it (the @property part in .h file).

Also, programming hint: break your lines into smaller statements so they are easier to debug.

answered May 10, 2011 at 23:16

Rayfleck

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1 Comment

Alex Wayne Over a year ago

Only if the property has been declared as (retain), though.

Scott Rice · Accepted Answer · 2011-05-10 23:17:17Z

You are right, loadingStatus is being deallocated. That is because the value is being autoreleased.

If you change

loadingStatus = [NSDictionary dictionaryWithObjects:[NSArray arrayWithObjects:@"bad", nil] forKeys:[NSArray arrayWithObjects:@"amount", nil ] ];

to

loadingStatus = [NSDictionary dictionaryWithObjects:[NSArray arrayWithObjects:@"bad", nil] forKeys:[NSArray arrayWithObjects:@"amount", nil ] ];
[loadingStatus retain];

or

loadingStatus = [[NSDictionary alloc] initWithObjects:[NSArray arrayWithObjects:@"bad", nil] forKeys:[NSArray arrayWithObjects:@"amount", nil ] ];

then your code will work.

The reason for this is that the object that is returned from dictionaryWithObjects:forKeys has had autorelease called on it, so if you want to keep it from being deallocated, you need to call retain.

As a reference, if you call alloc/init, you get an object with a retain count of 1. If you use a method such as dictionaryWithObjects:forKeys: you get an object with a retain count of 0. To fix that problem, just add a retain and you will be good to go.

Apple has some really nice documentation on memory management. I recommend checking it out when you have the chance

Memory Management Guide

Memory Management Rules

Hope this helps!

-Scott

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