Q:

How to access custom UIViewController in a UISplitViewController from another class

I have a custom customUIViewController in a UISplitViewController and want to access the instance of the customUiViewController from the detailView (which is another UIViewController inside the UISplitViewController) from another class; how can I do this?
CODE SNIP (Dont worry about the syntax; it is shorten up)
myAppDelegate.m
customViewController *masterView = [[customViewController alloc] init;
UINavigationController *NVC = [[UINavigationController alloc] initWithRootViewController:masterView];

MYViewController *detailView = [[MyViewController alloc] init;

UISplitViewController *mySplit = [...];

mySplit.viewControllers = NSArray[...masterview,detailView,nil];

[window addSubView:mySplit view];

MyViewController.m   
 -(void) someMethod {
        customViewController *myInstance = (customViewController)[self.splitViewController objectAtIndex:0]; ??
 // I think this just gets the outter UINavigationController
        [myInstance doSomething];
 }

customViewController.m  
-(void) doSomething {
}

I want to be able to get access to customViewController to call the doSomething method. Both customViewController and myViewController is inside the same UISplitViewController

A:

UIViewControllers have a splitViewController property so try using that to get a reference:
customViewController *myInstance = 
    (customViewController *)[self.splitViewController.viewControllers 
                                 objectAtIndex:0];

Index 0 is the left-side view controller in the split view controller.
Edit:
If the left-side view controller is a UINavigationController, then to get the root view controller of that, do this:
UINavigationController *nc = 
    (UINavigationController *)[self.splitViewController.viewControllers 
                                objectAtIndex:0];

customViewController *myInstance = 
    (customViewController *)[nc.viewControllers objectAtIndex:0];

A:

If you're working with the default UISplitView that XCode makes, you need to reference the AppDelegate to get the splitView's ivar:
YourAppDelegate *del = (YourAppDelegate *)[[UIApplication sharedApplication]delegate];
UISplitViewController *split = del.splitViewController;
NSArray *vcArray = split.viewControllers;
//left is objectAtIndex:0, right is objectAtIndex:1

