How do I declare class-level properties in Objective-C

Question

Maybe this is obvious  but I don t know how to declare class properties in Objective-C   I need to cache per-class a dictionary and wonder how put it in the class

User · Answer

I m using this solution    interface Model    int  value     void  setValue  int val   end   implementation Model static int value     int  value    synchronized self    return value         void  setValue  int val    synchronized self    value   val       end   And i found it extremely useful as a replacement of Singleton pattern   To use it  simply access your data with dot notation   Model value   1  NSLog    d   value   Model value

User · Answer

As of Xcode 8 Objective-C now supports class properties    interface MyClass   NSObject  property  class  nonatomic  assign  readonly  NSUUID  identifier   end   Since class properties are never synthesised you need to write your own implementation    implementation MyClass static NSUUID  identifier   nil      NSUUID   identifier     if   identifier    nil         identifier     NSUUID alloc  init         return  identifier     end   You access the class properties using normal dot syntax on the class name   MyClass identifier

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Here s a thread safe way of doing it      Foo h  interface Foo        NSDictionary   dictionary      Foo m   NSDictionary   dictionary     static NSDictionary  fooDict   nil     static dispatch once t oncePredicate     dispatch once  amp oncePredicate                create dict            return fooDict      These edits ensure that fooDict is only created once   From Apple documentation   dispatch once - Executes a block object once and only once for the lifetime of an application

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Starting from Xcode 8  you can use the class property attribute as answered by Berbie   However  in the implementation  you need to define both class getter and setter for the class property using a static variable in lieu of an iVar   Sample h   interface Sample  NSObject  property  class  retain  Sample  sharedSample   end   Sample m   implementation Sample static Sample   sharedSample      Sample   sharedSample      if   sharedSample  nil           Sample setSharedSample  sharedSample           return  sharedSample        void setSharedSample  Sample   sample       sharedSample     Sample alloc init      end

User · Answer

Properties have values only in objects  not classes   If you need to store something for all objects of a class  you have to use a global variable  You can hide it by declaring it static in the implementation file   You may also consider using specific relations between your objects  you attribute a role of master to a specific object of your class and link others objects to this master  The master will hold the dictionary as a simple property  I think of a tree like the one used for the view hierarchy in Cocoa applications   Another option is to create an object of a dedicated class that is composed of both your  class  dictionary and a set of all the objects related to this dictionary  This is something like NSAutoreleasePool in Cocoa

User · Answer

If you re looking for the class-level equivalent of  property  then the answer is  there s no such thing   But remember   property is only syntactic sugar  anyway  it just creates appropriately-named object methods   You want to create class methods that access static variables which  as others have said  have only a slightly different syntax

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As seen on WWDC 2016 XCode 8  what s new in LLVM session  5 05    Class properties  can be declared as follows  interface MyType   NSObject  property  class  NSString  someString   end  NSLog   quot format string    quot   MyType someString    Note that class properties are never synthesized  implementation static NSString    someString     NSString   someString   return  someString       void setSomeString  NSString   newString    someString   newString     end

User · Answer

If you have many class level properties then a singleton pattern might be in order  Something like this      Foo h  interface Foo     Foo   singleton    property 1      property 2      property 3       end   And     Foo m   import  Foo h    implementation Foo  static Foo   singleton   nil      Foo   singleton       if   singleton    nil   singleton     Foo alloc  init        return  singleton      synthesize property1   synthesize property2   synthesise property3    end   Now access your class-level properties like this    Foo singleton  property1   value  value    Foo singleton  property2

User · Answer

properties have a specific meaning in Objective-C  but I think you mean something that s equivalent to a static variable  E g  only one instance for all types of Foo   To declare class functions in Objective-C you use the   prefix instead of - so your implementation would look something like      Foo h  interface Foo         NSDictionary   dictionary      Foo m    NSDictionary   dictionary     static NSDictionary  fooDict   nil    if  fooDict    nil           create dict       return fooDict

User · Answer

Try this solution it s simple  You can create a static variable in a Swift class then call it from any Objective-C class

[objective-c] How do I declare class-level properties in Objective-C?

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