问题
I am trying to convert non-ARC project to use ARC but for some reason its complaining about the use of all instance variables.
@property (nonatomic,retain)id myvariable;
results in
Error : "Use of undeclared variable _myvariable"
there are some places in my code where I don't want to modify retain count but do an assignment to the property. so I use an instance variable.
adding @syhtnesize myvariable =_myvariable resolves this problem but I am trying to figure out the right way to fix this.
Possible solutions:
1) Add synthesize
2) replace use of instance variable with self.myvariable and make property assigned.
EDIT: Extension of problem ARC errors
回答1:
It sounds like you've hit a backward compatibility feature.
Since Xcode 4.4 property declarations no longer require an @synthesize statement and without one the compiler auto-generates an _propertyName instance variable.
However with an @synthesize propertyName, as you would pre-Xcode 4.4, then the compiler will auto-generate an propertyName - note no underscore - instance variable.
The compiler messages warning you "Use of undeclared variable _myvariable" suggest you have switched the code to use underscores but still have some @synthesize myvariable statements.
Your use of @synthesize myvariable = _myvariable specifies the name to use for the instance variable directly, and so solves your problem, but removing the @synthesize completely is the usual approach.
回答2:
With all the arc stuff
@property (nonatomic, strong) Something *myVariable;
is accessible by both
self.myVariable;
and
_myVariable;
No need to use @synthesize
回答3:
It depends what you need. If you declare property:
@property (strong) NSString *myvariable;
And you want to change name of the private ivar to something different that _myvariable you have to add
@synthesize myvariable = _myVarNewName
but if you want to use exactly the same name with underscore on the front just remove @synthesize (works with iOS 6 and above) and the compiler do the rest so you can access the private variable like _myvariable or public like self.myvariable.
来源：https://stackoverflow.com/questions/21172172/arc-complaining-about-instance-vairiables