Difference in synthesize property in objective C

Question

Code in .h file

@property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext;

Code in .m file

@synthesize managedObjectContext = __managedObjectContext;

I'm a beginner in objective c , I wonder what is difference between @synthesize managedObjectContext; and @synthesize managedObjectContext = __managedObjectContext; can some explain?

Thanks for those links, very useful Sorry i didn't looked that earlier — Dolo, Apr 04 '13 at 11:17

score 3 · Accepted Answer · answered Apr 04 '13 at 11:11

The @synthesize propertyName creates a variable to back the property with the same name as the property, while @synthesize propertyName = variableName gives the variable an alternative name (perhaps the property name prefixed with an underscore).

Note that in the compilers shipped with the most recent version of Xcode using @synthesize is no longer necessary: the compiler figures out what properties need synthesizing, and implicitly inserts

@synthesize propertyName = _propertyName;

for each property that needs to be synthesized.

score 0 · Answer 2 · edited May 23 '17 at 12:13

If you use

@synthesize managedObjectContext = __managedObjectContext;

you can write lines like this:

__managedObjectContext = someContext;

and it will change the value stored in this property by directly accessing it, without the setManagedObjectContext: method.

However, this line will be incorrect (unless you declare some other managedObjectContext before it):

managedObjectContext = someContext; //wrong
self.managedObjectContext = someContext; //good

P.S. Btw, What exactly does @synthesize do?

Difference in synthesize property in objective C

2 Answers2