CODEWITHSUNDEEP
iosproperties
Lucas Pereira
Lucas Pereira

Reputation: 569

Accessing a value of a class's variable from another - objective-c

This is probably a silly question but I'm having a hard time trying to solve it. The thing is that a have a class that implements a counter and at the end of it procedures it calls a view controlled by another class. What I'd like to do is access the value of the counter of the first class from the second one. I defined the counter as a property and tried to access it from the other class but I always get its value as 0. Can anyone help me out?

thanks.

What i have is this:

Class1.h

@interface Class1 : CCLayerColor <UIAlertViewDelegate>
{
    int movesCounter;
}
@property int movesCounter;

@end

Class1.m

@implementation Class1
@synthesize movesCounter;

//At this point the counter gets incremented and NSLogging its value correctly

@end

Class2.m 

#import Class1.h    

@implementation GameOverLayer


-(id) init
{
    if( (self=[super init]))
    {
       Class1 *theClass1 = [[Class1 alloc]init];
       NSString *message = [NSString stringWithFormat:@"It took you %d moves.",theClass1.movesCounter];
       UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"Alert" message:message delegate:self cancelButtonTitle:@"Ok" otherButtonTitles:nil, nil];

       [alert show];
       [alert release];
    }
}

What am I doing wrong?

Upvotes: 2

Views: 6689

Answers (2)

Dylan
Dylan

Reputation: 126

Your problem is that you're creating a new instance of Class1 in your Class2 init method:

Class1 *theClass1 = [[Class1 alloc] init];

This new instance is in addition to the one with the int you've been incrementing successfully, and as it's a fresh slice of memory, its value for movesCounter is still 0. What you really want is a pointer to the specific copy of Class1 that you've been working with -- no alloc / init needed or desired. Try making a property in Class2 that can hold your pointer to Class1:

#import "Class1.h"

@interface Class2 : NSObject {
    Class1 *myPointerToClass1;
}
@property (nonatomic, retain) Class1 *myPointerToClass1;

And of course @synthesize myPointerToClass1 in the .m of Class2. Now that Class2 is ready to hold a pointer to Class1, you need simply to populate it. In Class1, after the code that alloc's and init's the Class2 instance, use code like this:

myClass2.myPointerToClass1 = self;

Just to make sure I haven't forgotten anything I did all this using your code above and everything worked just fine for me.

EDIT: original answer begins here, but is now irrelevant..... You mention having defined the counter as a property, but have you also synthesized the instance variable in your implementation (.m) file?

@synthesize myCounter;

This will create the setter and getter methods automatically for you. Also, have you verified that the value is being incremented at all, perhaps with an NSLog statement in the viewcontroller?

NSLog(@"myCounter is currently equal to %d", myCounter); // assuming an int

If these basics are covered, maybe you could edit your question to include the code showing us more about how the misbehaving class is getting this pointer to the variable in the first place.

Upvotes: 2

John Estropia
John Estropia

Reputation: 17500

In your header file you declare your iVar as

{
    int movesCounter;
}

but you synthesize the property with

@synthesize movesCounter = _movesCounter; // note the underscore

so the movesCounter iVar does not get connected to the movesCounter property. If you are updating just movesCounter instead of self.movesCounter or _movesCounter then external classes will not be able to see these changes.

Upvotes: 1

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