Question

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Properties and Instance Variables in Objective-C 2.0

What is the difference when I use @property and @synthesize in first case, and @property and @synthesize and also declare same instance variable? Because both seem to work.

Answer 1

There is no difference: the instance variable that you declare will be used, and its ARC properties will be overridden by these of your declared @property.

A property’s specified ownership is preserved in its metadata, but otherwise the meaning is purely conventional unless the property is synthesized. If a property is synthesized, then the associated instance variable is the instance variable which is named, possibly implicitly, by the @synthesize declaration. If the associated instance variable already exists, then its ownership qualification must equal the ownership of the property; otherwise, the instance variable is created with that ownership qualification.

Declaring an instance variable for a property that you intend to @synthesize is best avoided. If you prefer an instance variable with a different name, you can use the synthesize syntax with the ivar name:

@synthesize myproperty = _myivar;