UIViewController子类（模仿UITableViewController）没有被释放

Question

I have subclassed UIViewController , which mimics UITableViewController == HUDTableViewController . Then I subclass from this subclassed view controller ( SomeViewController : HUDTableViewController ).

If I simulate a memory warning, SomeViewController doesn't get released. Here is the code of HUDTableViewController :

using System;

using Foundation;
using UIKit;

namespace MyApp
{
    public class HUDTableViewController : UIViewController, IUITableViewDataSource, IUITableViewDelegate, IDisposable, IUIScrollViewDelegate
    {
        private UIView parentView;
        private UITableView tableView;

        public UITableView TableView
        {
            get
            {
                return this.tableView;
            }
            set
            {
                this.tableView = value;
            }
        }

        public HUDTableViewController() : base()
        {
            Initialize();
        }

        private void Initialize()
        {
            this.tableView = new UITableView();
            this.tableView.TranslatesAutoresizingMaskIntoConstraints = false;

            this.tableView.WeakDelegate = this;
            this.tableView.WeakDataSource = this;

            this.parentView = new UIView();
        }

        public override void ViewDidLoad()
        {
            base.ViewDidLoad();

            this.parentView.AddSubview(this.tableView);
            View = this.parentView;

            NSMutableDictionary viewsDictionary = new NSMutableDictionary();
            viewsDictionary["parent"] = this.parentView;
            viewsDictionary["tableView"] = this.tableView;

            this.parentView.AddConstraints(NSLayoutConstraint.FromVisualFormat("H:|[tableView]|", (NSLayoutFormatOptions)0, null, viewsDictionary));
            this.parentView.AddConstraints(NSLayoutConstraint.FromVisualFormat("V:|[tableView]|", (NSLayoutFormatOptions)0, null, viewsDictionary));
        }

        [Foundation.Export("numberOfSectionsInTableView:")]
        public virtual System.nint NumberOfSections(UIKit.UITableView tableView)
        {
            return 1;
        }

        public virtual System.nint RowsInSection(UIKit.UITableView tableview, System.nint section)
        {
            throw new NotImplementedException();
        }

        public virtual UIKit.UITableViewCell GetCell(UIKit.UITableView tableView, Foundation.NSIndexPath indexPath)
        {
            throw new NotImplementedException();
        }

        [Export("tableView:estimatedHeightForRowAtIndexPath:")]
        public virtual System.nfloat EstimatedHeight(UIKit.UITableView tableView, Foundation.NSIndexPath indexPath)
        {
            return UITableView.AutomaticDimension;
        }

        [Foundation.Export("tableView:didSelectRowAtIndexPath:")]
        public virtual void RowSelected(UIKit.UITableView tableView, Foundation.NSIndexPath indexPath)
        {
        }

        [Export("tableView:heightForRowAtIndexPath:")]
        public virtual System.nfloat GetHeightForRow(UIKit.UITableView tableView, Foundation.NSIndexPath indexPath)
        {
            return 44.0f;
        }

        [Foundation.Export("tableView:heightForHeaderInSection:")]
        public virtual System.nfloat GetHeightForHeader(UIKit.UITableView tableView, System.nint section)
        {
            return UITableView.AutomaticDimension;
        }

        [Foundation.Export("tableView:viewForHeaderInSection:")]
        public virtual UIKit.UIView GetViewForHeader(UIKit.UITableView tableView, System.nint section)
        {
            return null;
        }

        [Export("tableView:titleForHeaderInSection:")]
        public virtual string TitleForHeader(UITableView tableView, nint section)
        {
            return string.Empty;
        }

        [Foundation.Export("tableView:willDisplayCell:forRowAtIndexPath:")]
        public virtual void WillDisplay(UIKit.UITableView tableView, UIKit.UITableViewCell cell, Foundation.NSIndexPath indexPath)
        {
        }
    }
}

tableView should have a reference count of 2 (because of AddSubView and my property).

This is the main view controller, which instantiates SomeViewController :

public class MasterViewContainer : UIViewController
{
    private bool hasSetupHandlersAndEvents = false;
    // ...

    public override void ViewWillAppear (bool animated)
    {
        base.ViewWillAppear (animated);

        if (!hasSetupHandlersAndEvents) {
            if (listButton != null) {
                listButton.Clicked += listButton_Clicked;
            }
            hasSetupHandlersAndEvents = true;
        }
    }

    public override void ViewWillDisappear (bool animated)
    {
        base.ViewWillDisappear (animated);

        if (hasSetupHandlersAndEvents) {
            if (listButton != null) {
                listButton.Clicked -= listButton_Clicked;
            }
            hasSetupHandlersAndEvents = false;
        }
    }

    private void listButton_Clicked(object sender, EventArgs args){
        SomeViewController viewController = new SomeViewController();
        viewController.SomeEvent += SomeEventHandler;
        NavigationController.PushViewController(viewController, false);
    }
}

As you can see SomeViewController has a reference to MasterViewContainer , because of SomeEventHandler .

SomeViewController is released if I use

public class SomeViewController : UITableViewController

, but it isn't released if I use

public class SomeViewController : HUDTableViewController

The Dispose method is never called. I don't see a reference cycle. Where do I have to release something? What I'm missing?

Try 1:

This is the only solution, which comes to my mind. I use a field (class variable) where I hold the reference to SomeViewController . In DidReceiveMemoryWarning I manually release/dispose it. When I want to access the field, I check if it has been initialised before. If not I initialise it when needed.

public class MasterViewContainer : UIViewController
{
    private SomeViewController viewController;

    public override void DidReceiveMemoryWarning ()
    {
        // Releases the view if it doesn't have a superview.
        base.DidReceiveMemoryWarning ();

        // Release any cached data, images, etc that aren't in use.
        if (this.viewController != null)
        {
            this.viewController.SomeEvent -= SomeEventHandler;
            this.viewController.Dispose();
            this.viewController = null;
        }
    }

    private void listButton_Clicked(object sender, EventArgs args){
        if (this.viewController == null)
        {
            this.viewController = new SomeViewController();
            this.viewController.SomeEvent += SomeEventHandler;
        }

        NavigationController.PushViewController(this.viewController, false);
    }

But this solution isn't perfect. The dispose is also called when the view is currently on screen. So it is very likely to have malfunctions.

Bounty:

I'd like to have a solution, which explains the memory management issue. Why it doesn't get released? What has to change to get it released (without doing stuff like in my try). It should behave like UITableViewController .

Try 2:

Now I tried to override the Dispose(bool disposing) of HUDTableViewController :

protected override void Dispose(bool disposing)
{
    if(!this.disposed)
    {
        if(disposing)
        {
           this.tableView.RemoveFromSuperview();
           this.tableView.Dispose();
        }
        this.disposed = true;
    }
    base.Dispose(disposing);
}

Neither this Dispose method of HUDTableViewController nor the Dispose method of SomeViewController is called.

Answer 1

Call super if you are wanting your parent view to also call the same function handle your management from there. Depending on the arrangement you wouldn't need to do any other manual disposing.

public override void DidReceiveMemoryWarning ()
{
    // If you want the superclass to fire the function first call super first
    // and vice versa. 
    super.didReceiveMemoryWarning();
    // Releases the view if it doesn't have a superview.
    base.DidReceiveMemoryWarning ();