Current ChildView Controller - iphone

Question

I am trying to implement a SwipeGesture on my viewcontroller.
The issue I am facing currently is that I cannot determine what the currently displayed childview controller is.
The swipeGesture is added to the container view controller. And then must determine what is the currently displayed VC is in the parent-child relationship, then move to the right or left.

Answer 1

If you are talking about custom container view controller, it's the job of the container controller to keep track of this. So, you might have your own #property that keeps track of which one you're on, and adjust it as you transitionFromController as a result of a swipe. So you might have a numeric property that you increment as you go to the right and that you decrement as you go to the left.
In general (if you're just trying to keep track of which "from" controller you're passing to transitionFromViewController), there are two approaches. One approach is implied by listing 14-3 in Adding a child controller of the View Controller Programming Guide.
In this scenario, in viewDidLoad you perform addChildViewController for the first view controller with. You do not, in this scenario, load the other child view controllers via addChildViewController at this point, though, but rather you let your method that does the transitioning take care of that (as in Listing 14-3).
If you do it this way, you can just grab [self.childViewControllers lastObject], and that will be your "current" child controller. So, that might look like:
#interface ViewController ()
#property (nonatomic) NSInteger currentIndex;
#end
#implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
UIViewController *initialController = ... // set your initial controller
[self addChildViewController:initialController];
initialController.view.frame = self.containerView.bounds;
[self.containerView addSubview:initialController.view];
[initialController didMoveToParentViewController:self];
UISwipeGestureRecognizer *gesture;
gesture = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:#selector(handleSwipe:)];
gesture.direction = UISwipeGestureRecognizerDirectionRight;
[self.containerView addGestureRecognizer:gesture];
gesture = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:#selector(handleSwipe:)];
gesture.direction = UISwipeGestureRecognizerDirectionLeft;
[self.containerView addGestureRecognizer:gesture];
}
- (void) handleSwipe:(UISwipeGestureRecognizer *)gesture
{
if (gesture.direction == UISwipeGestureRecognizerDirectionLeft && self.currentIndex < (kMaxIndex - 1))
{
self.currentIndex++;
UIViewController *newController = ... // set your new controller
UIViewController *oldController = [self.childViewControllers lastObject];
[self cycleFromViewController:oldController
toViewController:newController
direction:gesture.direction];
}
else if (gesture.direction == UISwipeGestureRecognizerDirectionRight && self.currentIndex > 0)
{
self.currentIndex--;
UIViewController *newController = ... // set your new controller
UIViewController *oldController = [self.childViewControllers lastObject];
[self cycleFromViewController:oldController
toViewController:newController
direction:gesture.direction];
}
}
- (void) cycleFromViewController:(UIViewController*) oldController
toViewController:(UIViewController*) newController
direction:(UISwipeGestureRecognizerDirection)direction
{
[oldController willMoveToParentViewController:nil];
[self addChildViewController:newController];
newController.view.frame = oldController.view.frame;
UIViewAnimationOptions options;
if (direction == UISwipeGestureRecognizerDirectionRight)
options = UIViewAnimationOptionTransitionFlipFromLeft;
else if (direction == UISwipeGestureRecognizerDirectionLeft)
options = UIViewAnimationOptionTransitionFlipFromRight;
[self transitionFromViewController:oldController
toViewController:newController
duration:0.33
options:options
animations:^{
[oldController removeFromParentViewController];
}
completion:^(BOOL finished) {
[newController didMoveToParentViewController:self];
}];
}
The other model that I've seen some people do is to load all of the potential child controllers via addChildViewController in viewDidLoad. I don't personally like this approach, but I know people do it this way and it works fine.
But if you do it this way, you can no longer rely upon childViewControllers to know which controller is the current one. In that case, you have to define your own class property for the currentChildController. So it might look something like:
#interface ViewController ()
#property (nonatomic, strong) UIViewController *currentChildController;
#property (nonatomic) NSInteger currentIndex;
#end
#implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
[self addChildViewController:[self.storyboard instantiateViewControllerWithIdentifier:#"ChildOne"]];
[self addChildViewController:[self.storyboard instantiateViewControllerWithIdentifier:#"ChildTwo"]];
[self addChildViewController:[self.storyboard instantiateViewControllerWithIdentifier:#"ChildThree"]];
self.currentChildController = self.childViewControllers[0];
self.currentChildController.view.frame = self.containerView.bounds;
[self.containerView addSubview:self.currentChildController.view];
for (UIViewController *controller in self.childViewControllers)
[controller didMoveToParentViewController:self];
UISwipeGestureRecognizer *gesture;
gesture = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:#selector(handleSwipe:)];
gesture.direction = UISwipeGestureRecognizerDirectionRight;
[self.containerView addGestureRecognizer:gesture];
gesture = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:#selector(handleSwipe:)];
gesture.direction = UISwipeGestureRecognizerDirectionLeft;
[self.containerView addGestureRecognizer:gesture];
}
- (void) cycleFromViewController:(UIViewController*) oldController
toViewController:(UIViewController*) newController
direction:(UISwipeGestureRecognizerDirection) direction
{
self.currentChildController = newController;
newController.view.frame = oldController.view.frame;
UIViewAnimationOptions options;
if (direction == UISwipeGestureRecognizerDirectionRight)
options = UIViewAnimationOptionTransitionFlipFromLeft;
else if (direction == UISwipeGestureRecognizerDirectionLeft)
options = UIViewAnimationOptionTransitionFlipFromRight;
[self transitionFromViewController:oldController
toViewController:newController
duration:0.33
options:options
animations:^{
}
completion:nil];
}
- (void) handleSwipe:(UISwipeGestureRecognizer *)gesture
{
if (gesture.direction == UISwipeGestureRecognizerDirectionLeft && self.currentIndex < (kMaxIndex - 1))
{
self.currentIndex++;
UIViewController *oldController = self.currentChildController;
UIViewController *newController = self.childViewControllers[self.currentIndex];
[self cycleFromViewController:oldController
toViewController:newController
direction:gesture.direction];
}
else if (gesture.direction == UISwipeGestureRecognizerDirectionRight && self.currentIndex > 0)
{
self.currentIndex--;
UIViewController *oldController = self.currentChildController;
UIViewController *newController = self.childViewControllers[self.currentIndex];
[self cycleFromViewController:oldController
toViewController:newController
direction:gesture.direction];
}
}
Those are the two logical approaches.
By the way, the first approach doesn't preclude having your own class property to know which controller you're on, and sometimes that's useful (e.g. if the type of animation you employ is contingent upon whether you're going to the "right" or to the "left), but unless that's the case, you can get away with just looking at [self.childViewControllers lastObject].

Answer 2

In a project i'm working on, I have many View Controllers each with their own Navigation Controller added to a Parent View Controller. I know the initial entry child, but I do the following to find the currently displayed children of the child:
[myKnownViewController.childViewControllers objectAtIndex:0].navigationController.topViewController