iPhone Setting ViewController nested in NSMutableArray

Question

Hello I'm trying to set attributes for a viewcontroller nested inside a NSMutableArray, for example I have 3 ViewController inside this array:

FirstViewController *firstViewController = [FirstViewController alloc];
SecondViewController *secondViewController = [SecondViewController alloc];
ThirdViewController *thirdViewController = [ThirdViewController alloc];


NSMutableArray *viewControllerClasses = [[NSMutableArray alloc] initWithObjects:
                                         firstViewController,
                                         secondViewController,
                                         thirdViewController,                                       
                                         nil];


for (int x=0; x<[viewControllerClasses count]; x++) {

    // as an example to set managedObjectContext I otherwise would set firstViewController.managedObjectContext = context;

    [viewControllerClasses objectAtIndex:x].managedObjectContext = context;
}

But this results in an error: Request for member "managedObjectContext" in something not a structure or union. Shouldn't be "firstViewController" be the same as [viewControllerClasses objectAtIndex:0]?

Answer 1

The -objectAtIndex: method returns an id , which the dot-syntax cannot be applied on because the compiler can't determine the getter.

Anyway, you should just use fast enumeration ( for / in loop), and you could give a static type so the dot-syntax can be used (assuming FirstViewController and the rest inherits from BaseViewController):

for (BaseViewController* ctrler in viewControllerClasses)
   ctrler.managedObjectContext = context;

Also, you could revert to use brackets:

for (BaseViewController* ctrler in viewControllerClasses)
   [ctrler setManagedObjectContext:context];

(and please -init… immediately after +alloc .)

Answer 2

您可以尝试强制转换[viewControllerClasses objectAtIndex:x]返回不具有managedObjectContext属性的NSObject ，因此请尝试使用((FirstViewController *)[viewControllerClasses objectAtIndex:x]).managedObjectContext = context;