How to cast an object in Objective-C

Question

Is there a way to cast objects in objective-c much like the way objects are cast in VB NET   For example  I am trying to do the following      create the view controller for the selected item FieldEditViewController  myEditController  switch  selectedItemTypeID        case 3          myEditController     SelectionListViewController alloc  init           myEditController list   listOfItems          break      case 4             set myEditController to a diff view controller         break        load the view  self navigationController pushViewController myEditController animated YES    myEditController release      However I am getting a compiler error since the  list  property exists in the SelectionListViewController class but not on the FieldEditViewController even though SelectionListViewController inherits from FieldEditViewController   This makes sense  but is there a way to cast myEditController to a SelectionListViewController so I can access the  list  property   For example in VB NET I would do   CType myEditController  SelectionListViewController  list   listOfItems   Thanks for the help

User · Answer

Casting for inclusion is just as important as casting for exclusion for a C   programmer   Type casting is not the same as with RTTI in the sense that you can cast an object to any type and the resulting pointer will not be nil

User · Answer

Sure  the syntax is exactly the same as C - NewObj  pNew    NewObj  oldObj   In this situation you may wish to consider supplying this list as a parameter to the constructor  something like      SelectionListViewController - id  initWith  SomeListClass  anItemList     self    super init      if   self          self setList  anItemList          return self      Then use it like this   myEditController     SelectionListViewController alloc  initWith  listOfItems

User · Answer

Remember  Objective-C is a superset of C  so typecasting works as it does in C   myEditController     SelectionListViewController alloc  init     SelectionListViewController   myEditController  list   listOfItems

User · Answer

SelectionListViewController   myEditController  list   More examples   int i    int 19 5f      precision is lost  id someObject    NSMutableArray new      you don t need to cast id explicitly

User · Answer

Typecasting in Objective-C is easy as   NSArray  threeViews      UIView new    UIView new    UIView new    UIView  firstView    UIView   threeViews 0     However  what happens if first object is not UIView and you try to use it   NSArray  threeViews      NSNumber new    UIView new    UIView new    UIView  firstView    UIView   threeViews 0   CGRect firstViewFrame   firstView frame     CRASH    It will crash  And it s easy to find such crash for this case  but what if those lines are in different classes and the third line is executed only once in 100 cases  I bet your customers find this crash  not you  A plausible solution is to crash early  like this   UIView  firstView    UIView   threeViews 0   NSAssert  firstView isKindOfClass  UIView class      firstView is not UIView      Those assertions doesn t look very nice  so we could improve them with this handy category    interface NSObject  TypecastWithAssertion     instancetype typecastWithAssertion  id object   end    implementation NSObject  TypecastWithAssertion      instancetype typecastWithAssertion  id object       if  object    nil          NSAssert  object isKindOfClass  self class      Object    is not kind of class      object  NSStringFromClass  self class         return object      end   This is much better   UIView  firstView    UIView typecastWithAssertion  threeViews 0      P S  For collections type safety Xcode 7 have a much better than typecasting - generics

[objective-c] How to cast an object in Objective-C

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