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I'm still new to Objective-C and having some difficulties trying to figure out the appropriate way to use assign, retain, copy, strong, etc. when setting a property.
For example, I have the following types declared - how should I be setting the properties?
@property (nonatomic, ??) NSMutableArray *myArray
@property (nonatomic, ??) NSString *myString
@property (nonatomic, ??) UIColor *myColor
@property (nonatomic, ??) int *myIn
@property (nonatomic, ??) BOOL *myBOOL
Thanks....
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Assign creates a reference from one object to another without increasing the source's retain count. Retain creates a reference from one object to another and increases the retain count of the source object.
Retain increases the retain count of an object by 1 and takes ownership of an object. Whereas copy will copy the data present in the memory location and will assign it to the variable so in the case of copy you are first copying the data from a location assign it to the variable which increases the retain count.
"assign" is the default. In the setter that is created by @synthesize, the value will simply be assigned to the attribute. My understanding is that "assign" should be used for non-pointer attributes. "retain" is needed when the attribute is a pointer to an object.
The goal of the @property directive is to configure how an object can be exposed. If you intend to use a variable inside the class and do not need to expose it to outside classes, then you do not need to define a property for it. Properties are basically the accessor methods.
To reiterate, it does depend on context. In an non-ARC situation:
@property (nonatomic, copy) NSMutableArray *myArray
@property (nonatomic, copy) NSString *myString
@property (nonatomic, retain) UIColor *myColor
//Note the change to an int rather than a pointer to an int
@property (nonatomic, assign) int myInt
//Note the change to an int rather than a pointer to an int
@property (nonatomic, assign) BOOL myBOOL
The copy on myArray is to prevent modification by another "owner" of the object you set. In an ARC project, things change a bit:
@property (nonatomic, copy) NSMutableArray *myArray
@property (nonatomic, copy) NSString *myString
@property (nonatomic, strong) UIColor *myColor
//Note the change to an int rather than a pointer to an int
@property (nonatomic, assign) int myInt
//Note the change to an int rather than a pointer to an int
@property (nonatomic, assign) BOOL myBOOL
The change is primarily to myColor in your situation. You wouldn't use retain as you aren't managing reference counting directly. The strong keyword is a way of asserting "ownership" of the property and similar to retain. An additional keyword is also provided, weak, that would typically be used in place of assign for object types. Apple's common example of a weak property is for delegates. I'd recommend going through the Transitioning to ARC Release Notes in addition to the Memory Management Guide a time or two as there is more nuance than can easily be covered in an SO post.
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