copying a custom object

问题:

I have an object called Layer that has some attributes and some methodes.

i need to pass Layer to a second view controller:

SecondVC *view = [self.storyboard instantiateViewControllerWithIdentifier:@"2VC"];
view.Layer = [[Layer alloc] initWithMapLayer:self.Layer];
view.delegate = self;

UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:view];
navController.modalTransitionStyle = UIModalTransitionStyleCoverVertical;

[self presentModalViewController:navController animated:YES];

in the SecondVC, i may change the attributes. I then return the Layer object back via a delegate;

-(void)done
{
    [self.delegate returnLayer:self.layer];

    [self dismissModalViewControllerAnimated:YES];
}

now my problem is that i am passing a pointer to my first view controller's Layer object and when i update the Layer in the second view controller, my first view controller's Layer object is also being updated.

because of this, i can't tell if it has been changed (if it has, i need to run some code).

how can i create a copy of my Layer object and pass that instead of a pointer to my first view controller's Layer object?

EDIT:

i did try use a second init method:

-(id)initWithLayer:(Layer *)Layer
{
    if (self = [super init])
    {
        self.call = [[FunctionCall alloc] init];        
        self.HUD = [[MBProgressHUD alloc] init];

        self.Layers = [[NSMutableDictionary dictionaryWithDictionary:Layer.Layers] copy];
        self.nameList = [[NSArray arrayWithArray:Layer.nameList] copy];
    }
    return self;
}

which did not work out.

EDIT2:

tried

Layer *copyLayer = [self.myLayer copy];

layerView.myLayer = copyLayer;

and got error

-[layer copyWithZone:]: unrecognized selector sent to instance 0xfc72c40
2012-06-12 11:15:28.584 Landscout[8866:1fb07] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[Layer copyWithZone:]: unrecognized selector sent to instance 0xfc72c40'

SOLVED:

i added a deep copy to the initWithLayer method:

for (id key in layer.layers)
{
    [newLayers setValue:[[layer.layers objectForKey:key] mutableCopy] forKey:[key mutableCopy]];
}

for (id name in layer.nameList)
{
    [newList addObject:[name mutableCopy]];
}

this gives me a copy of the Layer object

回答1:

You will need to implement copy function to your object

In your Layer.m

- (id)copy
{
    Layer *layerCopy = [[Layer alloc] init];

    //YOu may need to copy these values too, this is a shallow copy
    //If YourValues and someOtherValue are only primitives then this would be ok
    //If they are objects you will need to implement copy to these objects too
    layerCopy.YourValues = self.YourValues;
    layerCopy.someOtherValue = self.someOtherValue;

    return layerCopy;
}

Now in your calling function

//instead of passing self.Layer pass [self.Layer copy]
view.Layer = [[Layer alloc] initWithMapLayer:[self.Layer copy]];