Question

Sorry about the title being extremely vague, I’m new to Objective C and struggling a little with it. Basically I have the following section of code:

Graph *graph1 = [[Graph alloc] init];
[graph1 addNode:@"TEST"];

which is working to a degree. But I want to change it because the above code happens on a button press, and therefore I assume I am creating a new “*graph1” every time I do this. I thought I could simply change it to this:

if(self = [super init]) 
{
    [self setGraph: [[Graph alloc] init]];
}
return self;

Where the above is in the init method, and below is the modified function:

[graph addNode:@"TEST"];

However when debugging I’ve found addNode method is never called when it’s like this.

Thanks
Zac

This is testViewController.h

#import <UIKit/UIKit.h>
@class Graph;
@class Node;

@interface testViewController : UIViewController {

    Graph       *graph;
    UILabel     *label;

}


@property (nonatomic, retain) IBOutlet UILabel *label;
@property (nonatomic, retain) Graph *graph;

- (IBAction) buttonPressed:(id)sender;

@end

This is textViewController.m

#import "testViewController.h"
#import "Graph.h"
@implementation testViewController

@synthesize  label, graph;

- (id)init
{
    if(self = [super init]) 
    {
        [self setGraph: [[Graph alloc] init]];
    }
    return self;
}

- (IBAction)buttonPressed:(id)sender
{
    //Graph *graph1 = [[Graph alloc] init];
    [graph addNode:@"TEST"];


    Node *node1 = [[Node alloc] initWithLabel: @"LABEL"];
    label.text = node1.label;
}

Answer 1

The first thing that comes to mind is that graph is nil and thus invoking a method (sending a message) to it will result in nothing. An unwanted release will cause an EXC_BAD_ACCESS, and this seems to be not the case.

I suppose you are calling all of this in a UIViewController subclass, right? Are you sure the right init is called? If you are using a NIB you should override the -(id)initWithNibName:bundle: and place you code there. I guess the code is probably in the plain -(id)init, since you are calling [super init] and not [super initWithNibName:nameOrNil bundle:bundleOrNil], but this way, if initialize the controller with the NIB you custom code is never called and thus graph is nil.

By the way, if the graph property is (retain) you are also causing a memory leak in the init.