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!

Answer 1

Remember, Objective-C is a superset of C, so typecasting works as it does in C:

myEditController = [[SelectionListViewController alloc] init];
((SelectionListViewController *)myEditController).list = listOfItems;

Answer 2

((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

Answer 3

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];

Answer 4

Thanks for the quick replies everyone!