Differentiate between iVar and Method Parameter? - objective-c

Question

I have a property like this:
#property (nonatomic, strong) IBOutlet UIImageView *backgroundImageHolder;
I want to adjust the setter, and XCode fills out the method signature like this:
-(void)setBackgroundImageHolder:(UIImageView *)backgroundImageHolder {
However, to actually do anything in the method, I must change the parameter backgroundImageHolder to something like backgroundImageHolderIn. Is there any way to avoid this? Is there any way to set the iVar without reinvoking the setter (causing an endless loop), or just referring to the parameter again?
I just tried:
self->backgroundImageHolder = backgroundImageHolder;
but the compiler warns me anyway.
Note: I am using the automagically generated iVar that the compiler makes for the property, but by default its name is the same.

Answer 1

You can give tell the compiler how to name the generated ivar:
#synthesize propertyName = iVarName;
If there actually exists an ivar named iVarName that one is used. If it doesn't exist the compiler creates it for you.
Like:
#synthesize backgroundImageHolder = myBackgroundImageHolder;
Now you can access the instance variable myBackgroundImageHolder. You don't need to declare it in the interface first.

Answer 2

Well, the conflicting parameter name seems to be pretty well covered by now. Basically, you have to either:
Rename the incoming argument
Rename the synthesized iVar
Once you have a method argument that differs from the iVar you're attempting to set, you have everything you need to write a custom setter. To avoid the infinite loop, you have to not call the setter you're currently implementing, whether it be via dot syntax or method brace syntax. Instead, refer directly to the backing iVar. You'll need to take care to manually implement the memory management semantics you declared in the property though (assign vs. retain, etc.):
// Backed by _myProperty iVar.
- (void)setMyProperty:(NSInteger)myProperty {
// Insert custom code here...
[self setMyProperty:myProperty]; // Obviously bad.
self.myProperty = myProperty; // Less obviously bad (thanks dot syntax)
// but semantically identical to the previous line.
_myProperty = myProperty // Good, (assuming assign semantics).
}

Answer 3

Compiler warns you because when you declare #property it creates instance variable with exact same name as a property (and as a parameter of a setter method). One way to avoid it is to create differently named instance variable and then pair it with property using #synthesize like this:
// .h
#interface Foo : NSObject {
IBOutlet UIImageView *myfooImageView;
}
#property (nonatomic, retain) UIImageView *publicFooImageView;
// .m
#implementation Foo
#synthesize publicFooImageView=myfooImageView;
#end

Answer 4

The clearest thing to do would be this:
In your header, define an iVar for backgroundImageHolder like so
#interface Something : NSObject
{
IBOutlet UIImageView *_backgroundImageHolder
}
Notice the leading underscore.
Then in your .m file, use either the synthesize call like so:
#synthesize backgroundImageHolder=_backgroundImageHolder;
or just define the getter and setter methods yourself: Then you are able to access the ivar via "_backgroundImageHolder" without any danger of accidentally calling the setter again.