Swapping child views in a container view

Question

Let ContainerView be the parent container view with two child content views: NavigationView and ContentView.

I would like to be able to swap out the controller of ContentView with another view. For example, swapping a home page controller with a news page controller. Currently, the only way I can think to do this is by using a delegate to tell the ContainerView that I want to switch views. This seems like a sloppy way to do this because the ContainerViewController would end up having a bunch of special delegates for all of the subviews.

This also needs to communicate with the NavigationView which has information about which view is currently in the ContentView. For example: if the user is on the news page, the navigation bar within the navigation view will show that the news button is currently selected.

Question A: Is there a way to swap the controller in ContentView without a delegate method calling the ContainerView itself? I would like to do this programmatically (no storyboard).

Question B: How can I swap controllers in ContentView from the NavigationView without a delegate call? I would like to do this programmatically (no storyboard).

Answer 1

When you have child views that have their own view controllers, you should be following the custom container controller pattern. See Creating Custom Container View Controllers for more information.

Assuming you've followed the custom container pattern, when you want to change the child view controller (and its associated view) for the "content view", you would do that programmatically with something like:

UIViewController *newController = ... // instantiate new controller however you want
UIViewController *oldController = ... // grab the existing controller for the current "content view"; perhaps you maintain this in your own ivar; perhaps you just look this up in self.childViewControllers

newController.view.frame = oldController.view.frame;

[oldController willMoveToParentViewController:nil];
[self addChildViewController:newController];         // incidentally, this does the `willMoveToParentViewController` for the new controller for you

[self transitionFromViewController:oldController
                  toViewController:newController
                          duration:0.5
                           options:UIViewAnimationOptionTransitionCrossDissolve
                        animations:^{
                            // no further animations required
                        }
                        completion:^(BOOL finished) {
                            [oldController removeFromParentViewController]; // incidentally, this does the `didMoveToParentViewController` for the old controller for you
                            [newController didMoveToParentViewController:self];
                        }];

When you do it this way, there's no need for any delegate-protocol interface with the content view's controller (other than what iOS already provides with the Managing Child View Controllers in a Custom Container methods).

---

By the way, this assumes that the initial child controller associated with that content view was added like so:

UIViewController *childController = ... // instantiate the content view's controller any way you want
[self addChildViewController:childController];
childController.view.frame = ... // set the frame any way you want
[self.view addSubview:childController.view];
[childController didMoveToParentViewController:self];

---

If you want a child controller to tell the parent to change the controller associated with the content view, you would:

1. Define a protocol for this:

   @protocol ContainerParent <NSObject>
   
   - (void)changeContentTo:(UIViewController *)controller;
   
   @end
   

2. Define the parent controller to conform to this protocol, e.g.:

   #import <UIKit/UIKit.h>
   #import "ContainerParent.h"
   
   @interface ViewController : UIViewController <ContainerParent>
   
   @end
   

3. Implement the changeContentTo method in the parent controller (much as outlined above):

   - (void)changeContentTo:(UIViewController *)controller
   {
       UIViewController *newController = controller;
       UIViewController *oldController = ... // grab reference of current child from `self.childViewControllers or from some property where you stored it
   
       newController.view.frame = oldController.view.frame;
   
       [oldController willMoveToParentViewController:nil];
       [self addChildViewController:newController];
   
       [self transitionFromViewController:oldController
                         toViewController:newController
                                 duration:1.0
                                  options:UIViewAnimationOptionTransitionCrossDissolve
                               animations:^{
                                   // no further animations required
                               }
                               completion:^(BOOL finished) {
                                   [oldController removeFromParentViewController];
                                   [newController didMoveToParentViewController:self];
                               }];
   }
   

4. And the child controllers can now use this protocol in reference to the self.parentViewController property that iOS provides for you:

   - (IBAction)didTouchUpInsideButton:(id)sender
   {
       id <ContainerParent> parentViewController = (id)self.parentViewController;
       NSAssert([parentViewController respondsToSelector:@selector(changeContentTo:)], @"Parent must conform to ContainerParent protocol");
   
       UIViewController *newChild = ... // instantiate the new child controller any way you want
       [parentViewController changeContentTo:newChild];
   }