Subclassing and overriding a UIView created with a nib file - uiview

Question

Let's say I've created a subclass of UIView and I'm loading it with a nib file.
I do this:
MySubView.m
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
NSArray *nib = [[NSBundle mainBundle] loadNibNamed:#"MySubView" owner:self options:nil];
[self release];
self = [[nib objectAtIndex:0] retain];
self.tag = 1;
[self fire];
}
return self;
}
- (void)fire {
NSLog(#"Fired MySubView");
}
Now I want to create some variations, but I don't want to copy the nib file, so I try to subclass MySubView like this, changing the background color:
RedMySubView.m
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
self.backgroundColor = [UIColor redColor];
[self fire];
}
return self;
}
- (void)fire {
NSLog(#"Fired RedMySubView");
}
The view is created, the background color is changed, but the fire action is not overridden by the subclass. If I call the fire method, the result is Fired MySubView in the console.
How can I resolve this?
I want to keep the nib layout, but give it a new class.

Answer 1

I would say that with [self release] in the MySubview initializer initWithFrame you are throwing away the class you want to create with the initializer. The class is loaded by the loadNibName method and therefore has the same class as defined in the nib.
So it is useless to call the initializer in the subclass.
Try to implement your own nib constructor in MySubview (e.g. initWithNibFile):
- (id) initWithNibFile:(NSString *) nibName withFrame:(CGRect) frame
etc. and call this constructor in RedMySubview
- (id) initWithNibFile:(NSString *) nibName withFrame:(CGRect) frame {
self = [super initWithNibFile:mynib withFrame:MyCGRect];
if (self)
....
If you now look up that your nib file really has RedMySubview as class, fire should be
overridable. If you use both MySubview and RedMySubview, you must duplicate the xib.
Or you create an abstract class (a stub) which implements only the initWithNibFile initializer and the UIViews you want to create are subclasses of it:
MyAbstractNibUIView initWithNibFile:withFrame:
MyRedSubview : MyAbstractNibUIView red.xib
MyGreenSubview :MyAbstractNibUIView green.xib
MyBlueSubview : MyAbstractNibUIView blue.xib

Answer 2

When you call self = [[nib objectAtIndex:0] retain] you basically override your "self" object to become a MySubView, since a MySubView is the base object in the nib file. This is undesired because if the calling class is a RedMySubView, then it will be overridden into a MySubView.
Instead you want to change your - (id)initWithFrame:(CGRect)frame in MySubView into this:
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
NSArray *nib = [[NSBundle mainBundle] loadNibNamed:#"MySubview" owner:self options:nil];
// The base of the nib file. Don't set self to this, instead copy all of its
// subviews, and "self" will always be the class you intend it to be.
UIView *baseView = [nib objectAtIndex:0];
// Add all the subviews of the base file to your "MySubview". This
// will make it so that any subclass of MySubview will keep its properties.
for (UIView *v in [baseView subviews])
[self addSubview:v];
self.tag = 1;
[self fire];
}
return self;
}
Now, everything should work in the initializer of "MyRedSubView", except that fire will fire twice, since you call it both in MySubView and RedMySubView.