When should I dispose of objects in Xamarin.IOS native?

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I am building an application that uses a shared project to hold its business logic.

In this shared project each controller has an equivalent.

I use the ViewDidLoad method to generate the logic for the controller and attach it to itself like this:

    public override void ViewDidLoad() {
        base.ViewDidLoad();
        _logic = new MyControllerLogic();
        _logic.attach(this);
    }

Each logic has its own instance variables etc that should be disposed when they are not used

So when (for example) I navigate backwards from MyController to MyFirstController or if I replace the application's root view controller , the logic behind the navigated out of/replaced controller has to be disposed.

Where should I do this?

In the android part of the project I did it like this:

    protected override void OnPause() {
        base.OnPause();
        if (IsFinishing) {
            _logic?.detach();
            _logic = null;
        }
    }

You should use an Unwind Segue on the view controller, this is the only reliable way of knowing when a view controller has been dismissed:

https://developer.apple.com/library/archive/technotes/tn2298/_index.html

Here is a Xamarin example:

https://github.com/xamarin/recipes/tree/master/Recipes/ios/general/storyboard/unwind_segue

On which object and when we have to use dispose(), part of Xamarin, manage ressources is more complicated than in android native Dispose(); } else { /* Android's ListView reuses list items when they aren't need For this reason, you need to make sure all views that should change, will​  Find Xamarin Development. Get Useful Information In Seconds. Visit Today & Quickly Get More Results On Fastquicksearch.com

Xamarin is C# based an uses the C# garbage collector. The most you should do is call is GC.Collect();

If you want fine-grained control over memory management, you should use Swift or Objective-C.

Garbage Collection, Samples. Xamarin.Forms Samples · Android Samples · iOS Samples Managed objects: types which do not inherit from Java. The native peer is an instance of a Java class within the Android runtime VM, You should not dispose of this instance, as Java will attempt to invoke methods on it in the future:. When should I dispose of objects in Xamarin.IOS native? Ask Question Asked 1 year, 4 months ago. Active 1 year, 3 months ago. Viewed 225 times 0. I am building an

For those wandering this is the approach I ended up with (this works for Xamarin but it is adaptable to Swift if one needs to):

I created the following class ,and from now on all my UIViewControllers will extend this class

public abstract class BaseViewController : UIViewController {
    protected virtual void Finished() { }

    protected virtual void backPressed() { } //this is just in case I wish to be notified when the user moves back

    public override void ViewWillDisappear(bool animated) {
        base.ViewWillDisappear(animated);
        if (NavigationController != null && NavigationController.ViewControllers.ToList().FirstOrDefault(c => c == this) == null) {
            backPressed();
            Finished();
        }
    }

    public override void DismissViewController(bool animated, [BlockProxy(typeof(AdAction))] Action completionHandler) {
        base.DismissViewController(animated, completionHandler);
        Finished();
    }


    public void Present(string storyboard, bool replace = false, bool animated = true) {
        UIViewController vctl = UIStoryboard.FromName(storyboard, null).InstantiateInitialViewController();
        if (replace) {
            List<UIViewController> old = new List<UIViewController>();
            if (UIApplication.SharedApplication.KeyWindow.RootViewController is UINavigationController nav) {
                old.AddRange(nav.ViewControllers);
            } else {
                old.Add(UIApplication.SharedApplication.KeyWindow.RootViewController);
            }
            if (animated) {
                UIView.Transition(
                    UIApplication.SharedApplication.KeyWindow
                    , 0.25
                    , UIViewAnimationOptions.TransitionCrossDissolve
                    , () => UIApplication.SharedApplication.KeyWindow.RootViewController = vctl
                    , () => {
                        old.ForEach(o => (old as BaseViewController)?.Finished());
                    });
            } else {
                UIApplication.SharedApplication.KeyWindow.RootViewController = vctl;
                old.ForEach(o => (old as BaseViewController)?.Finished());
            }
        } else {
            this.PresentViewController(vctl, animated, null));
        }
    }

    public void AddController(string storyboard, string controller = null, bool animated = true) {
        UIViewController ctl = getController(storyboard, controller);
        this.NavigationController?.PushViewController(ctl, animated);
    }

    public static void ReplaceController(this UINavigationController me, string storyboard, string controller = null, bool animated = true) {
        UIViewController ctl = getController(storyboard, controller);
        UIViewController[] vcl = this.NavigationController?.ViewControllers;
        if (vcl == null) return;
        if (vcl.Length > 0) {
            UIViewController old = vcl[vcl.Length - 1];
            vcl[vcl.Length - 1] = ctl;
            me.SetViewControllers(vcl, animated);
            (old as BaseViewController)?.Finished();
        } else {
            me.PushViewController(ctl, animated);
        }

    }

    private UIViewController getController(string storyboard, string controller = null) {
        if (string.IsNullOrWhiteSpace(controller)) {
            return UIStoryboard.FromName(storyboard, null).InstantiateInitialViewController();
        }
        return UIStoryboard.FromName(storyboard, null).InstantiateViewController(controller);
    }

}

The only downside is that from now on I have to always use Present to show new Controllers and Add/ReplaceController to show new Controllers inside the current Navigation.

If someone has a better idea please tell me, because I will have to do the above for all types of controllers (UITabBarController etc etc) and that could be difficult to maintain.

Xamarin.iOS, the garbage collector and me, A lot has been written about the Garbage Collector and Xamarin.iOS. We do not keep a reference around to the CustomView object anywhere Dispose() – this will immediately release it together with the native image data  Garbage Collection. 03/15/2018; 15 minutes to read +3; In this article. Xamarin.Android uses Mono's Simple Generational garbage collector.This is a mark-and-sweep garbage collector with two generations and a large object space, with two kinds of collections:

  1. First approach is to write your own navigation service and manage view controllers. And when you use GoBack, you can execute Dispose method for popped ViewController.
  2. Second one is use framework like MvvmLight, MvvmCross etc. which provides methods in ViewModel's(your business logic) when should you clean/dispose/unsubscribe and etc.

Code should be like this

public class NavigationService
{
   public void NavigateTo(string storyboardName)
   {
      //your logic to present storyboard
   }

   public void GoBack()
  {
     var poppedController = NavigationController.PopViewController(true);
     poppedController.Dispose(); //or your method where you want preclean data;
  }
}

Optimize memory usage in Xamarin apps, NET developers to write apps for Android, iOS, MacOS… in C#. the references and after disposing the wrapper, the native object can be  So the equivalent C# code in Xamarin.iOS would be: Now of course, you don’t even have to call Dispose, since the GC will do this work for you. This code also will not compile, because there is sadly, not a MakeItRain method available on NSObject--I will send Xamarin a bug report as soon as I get around to it. So how does Xamarin.iOS do it?

How to Prevent Memory Leak and Profiling in Xamarin Applications, In this article, you will learn how to prevent memory leak and profiling in Xamarin applications. Managed and the other one is the native part which at times Garbage The Dispose method performs an object clean up, so the garbage Create a new Xamarin Forms project using Visual Studio and Select  When using Xamarin.iOS and Xamarin.Android to build mobile apps with truly native look and feel, you will still need to write a platform-specific layer of code. Thus, at least a basic knowledge of native technologies (Java/Kotlin for Android and Objective-C/Swift for iOS) is required. This, however doesn’t apply to Xamarin.Forms.

Xamarin Blueprints, The OnAttached method is where we set up all native shadow effects. We start with Forms element that we are customizing. In the OnDetached method, we would normally dispose any objects that are no longer required. We must also add  Create a Xamarin.iOS Binding Project - Once we have a static library, we will use it to create a Xamarin.iOS binding project. The binding project consists of the static library we just created and metadata in the form of C# code that explains how the Objective-C API can be used.

Beginning Visual Studio for Mac: Build Cross-Platform Apps with , Build Cross-Platform Apps with Xamarin and . Dispose(); database. if false, the method returns the list of Item objects stored in the database. Forms and native APIs, and therefore it allows you to do anything you could do with Xamarin. Description A collection view with header causes a crash after navigating via the shell flyout. The bug is iOS only. On Android it works fine. The app wont crash if you use tabs. Steps to Reproduce

Comments
  • Unfortunately while that is quite helpful when navigating between controllers in the same storyboard, I also have a number of storyboards that group together a number of controllers that make sense to be together (I call them modules), so when one module wants to load another, it uses PresentViewController to show the next storyboard, and I haven't found a way to unwind from that, and trigger my dispose methods
  • I tried putting GC.Collect(); in every ViewDidAppear method, and that seems to trigger the Dispose() method of all views I have navigated out of, and that seems to work wonderfully, but I have a weird feeling that this could cause a problem, you see I use a lot of extra threads that run in the background and report to the app, but since I allow the user to navigate backwards when they think this is taking too long, the thread will keep on running, preventing GC.Collect() to actually call dispose, at least that is my theory, when I have some time I will test it