CODEWITHSUNDEEP
objective-ciosmacoscocoa
ikevin8me
ikevin8me

Reputation: 4313

Objective-C: Correct way to pass a property's reference into a method call

If I have a property like this:

@property(strong, readwrite, nonatomic) NSDate* aProperty;

and I want to pass the reference into another method, are these correct:

if([AnotherClass aMethod:&(self.aProperty)]) { ...
if([AnotherClass aMethod:&self.aProperty]) { ...

Upvotes: 3

Views: 7115

Answers (3)

Rob
Rob

Reputation: 437402

Considering your example:

if ([AnotherClass aMethod:&(self.aProperty)]) { ...

This obviously won't work because the dot notation is, effectively, using the getter accessor method. It's equivalent to:

if ([AnotherClass aMethod:&[self aProperty]]) { ...

You can easily imagine why the compiler is a little confused about this notation. The logical alternative would be to reference the ivar. Thus, (assuming you're using the underscore convention for the property's ivar) it might look like:

if ([AnotherClass aMethod:&_aProperty]) { ...

But that has all sorts of issues (bypassing setter, having issues about aMethod needing __strong attribute to override the default __autoreleasing as discussed here, etc.).

So, probably best, just have a local variable that receives the update, and then invoke the property's setter subsequent to that:

NSDate *date;
if ([AnotherClass aMethod:&date]) { ...

self.aProperty = date;

Upvotes: 12

Remizorrr
Remizorrr

Reputation: 2322

You can use KeyValue coding.

just send name of a property as NSString

- (void) method:(NSString*)propertyName
{
  [self setValue:[NSNumber numberWithInt:2] forKey:propertyName];
}

also a property is just to methods (set and get), so you can pass a selector

SEL selector = @selector(setProperty:);

- (void) method:(SEL)selector target:(id)target
{
  [target performSelector:selector withObject:[NSNumber numberWithInt:2]];
}

i prefer to use key value coding.

Upvotes: 10

Snips
Snips

Reputation: 6753

aProperty

is already a pointer to the NSDate object, so you just pass the pointer value along for 'call by reference'.

As the item is declared as a pointer, you can pass the reference using,

if([AnotherClass aMethod:aProperty]) { ...

where the prototype for aMethod is...

- (BOOL) aMethod:(NSDate *) aParameter;

(the above is true unless you really do want to pass a pointer to the property itself - to modify the pointer to the property itself, in which case I would question your design)

Upvotes: 2

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