Question

I’ve just figured out why some code has just failed to work. I’ve got something like the following:

@interface Client : NSObject {
    Connection *connection;
}

@property (retain) NSMutableDictionary *channels;

Followed by this implementation:

@implementation Client

@synthesize channels;

- (id)init
{
    self = [super init];
    if (self) {
         // do whatever I want
         NSMutableDictionary *dict = [[NSMutableDictionary alloc] init];
    }

    return self;
}

Any idea why channels has a memory address of 0x0 in the init constructor for this class? I can’t figure out for the life of me why this is happening. I’m definitely calling that constructor, and it should be synthesizing the property allowing me to do whatever I want with it.

Answer 1

Unless you explicitly set channels to a value, it will remain nil. Perhaps you meant to do the following in your init method?

if (self) {
     // do whatever I want
     channels = [[NSMutableDictionary alloc] init];
}

Two more ways to set channels:

[self setChannels:[NSMutableDictionary dictionary]]; //These two lines...
self.channels = [NSMutableDictionary dictionary];    //...are equivalent.

Note that in that case, because we are using your retain accessors, we use the autoreleased +dictionary rather than alloc/init, which would leak if not using ARC.

Of course, channels must also be properly released in -dealloc, if not using ARC:

- (void)dealloc
{
    [channels release];
}