How to Remove a Previous ViewController

问题

I am a student and pretty new to programming. I am trying to learn Objective-C/Swift in my spare time. I made a game using spriteKit with swift that has multiple menus/scenes.

I am trying to transition from one view controller to another. To do this I used this code:

@IBAction func PlayButtonPressed(sender: AnyObject) {
    let playStoryboard : UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
    let vc : UIViewController = playStoryboard.instantiateViewControllerWithIdentifier("playGame") as UIViewController
    self.presentViewController(vc, animated: true, completion: nil)
}

This works for transitioning to the new VC scene, however, I believe the previous VC is still in the stack and takes up memory, slowing down my program.

I've read on some other posts that you can use the navigation controller to remove VC. However, I do not have a navigation controller; only view controllers. I've seen some stuff about removeFromParentViewController() and view.removeFromSuperview(), but I don't really know how to implement it. Other than that I did not find an answer that I was looking for.

So the question I am asking is how do I remove the previous VC from the stack? Any help would be a appreciated! (would prefer the help to be in swift, but Objective-C would help also) Thank you in advance!

note for reference: I believe in Objective-C my code would look something like this:

-(IBAction) PlayButtonPressed: (id) sender {
    UIStoryboard *playStoryboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
    UIViewController *vc = [playStoryboard instantiateViewControllerWithIdentifier:@"playGame"];
    [self presentViewController:vc animated:YES completion:nil];
}

回答1:

As I can assume, view controller being presented on the screen was instantiated either automatically from main storyboard or by setting app's window.rootViewController property.

In either case you can set rootViewController again to be your vc. To change rootViewController of your app you need to replace this line of code:

self.presentViewController(vc, animated: true, completion: nil)

... with one of the options bellow.

"Navigate" without transition animation:

Objective-C

UIWindow *window = (UIWindow *)[[UIApplication sharedApplication].windows firstObject];
window.rootViewController = vc;

Swift

let window = UIApplication.sharedApplication().windows[0] as UIWindow;
window.rootViewController = vc;

"Navigate" with transition animation:

Objective-C

UIWindow *window = (UIWindow *)[[UIApplication sharedApplication].windows firstObject];
[UIView transitionFromView:window.rootViewController.view
                    toView:vc.view
                  duration:0.65f
                   options:UIViewAnimationOptionTransitionCrossDissolve // transition animation
                completion:^(BOOL finished){
                    window.rootViewController = vc;
                }];

Swift

let window = UIApplication.sharedApplication().windows[0] as UIWindow;
UIView.transitionFromView(
    window.rootViewController.view,
    toView: vc.view,
    duration: 0.65,
    options: .TransitionCrossDissolve,
    completion: {
        finished in window.rootViewController = vc
    })

Remarks: Once rootViewController value gets changed your original view controller reference count should became 0 hence it will be removed from the memory!

回答2:

I guess best implementation is to place the following at the previous View Controller - Swift

    // Override to remove this view from the navigation stack
    override func viewDidDisappear(animated: Bool) {
        super.viewDidDisappear(animated)
        // Remove self from navigation hierarchy
        guard let viewControllers = navigationController?.viewControllers,
            let index = viewControllers.indexOf(self) else { return }
        navigationController?.viewControllers.removeAtIndex(index)
    }

回答3:

Swift 3

This will remove the current view controller from the memor

override func viewDidDisappear(_ animated: Bool) {
    super.viewDidDisappear(animated)
    guard let viewControllers = navigationController?.viewControllers,
    let index = viewControllers.index(of: self) else { return }
    navigationController?.viewControllers.remove(at: index)
}

回答4:

First of all, you are using the modal presentation pattern, rather than a navigation stack pattern (UINavigationController). You can't get rid of the presenting view controller, nor should you, as it would break navigation.

The short answer here is that you don't need to worry about this. The amount of memory a view controller itself takes up is trivial and will be released automatically once there are no more references to it (one you dismiss it or pop it off a navigation stack).

The longer answer would depend on your specific implementation. If you are somehow in a situation where you infinitely increasing the size of a stack, then it is a problem. An example would be if you have a navigation flow where you can freely move between two "screens" but internally each screen keeps presenting a new one rather than just switching to an existing one. If you are experiencing something like this, then you would be best suited to using a UITabBarController or something similar, where you are able to navigate laterally between view controllers without creating new ones.

回答5:

For swift 3 you can replace

self.present(ViewController(), animated: false, completion: nil);

with

if let window = UIApplication.shared.keyWindow{
            window.rootViewController = UINavigationController(rootViewController: ViewController());
        }

来源：https://stackoverflow.com/questions/25109167/how-to-remove-a-previous-viewcontroller

标签

ios

objective-c

memory-management

uiviewcontroller

swift