How to break reference cycle between view controll

问题:

Consider this simple example:

public partial class TableViewController : UITableViewController
{
    public TableViewController (IntPtr handle) : base (handle)
    {
    }

    protected override void Dispose (bool disposing)
    {
        Console.WriteLine (String.Format ("{0} controller disposed - {1}", this.GetType (), this.GetHashCode ()));

        base.Dispose (disposing);
    }

    public override void ViewDidLoad ()
    {
        //TableView.Source = new TableSource(this);
        TableView.Source = new TableSource();
    }
}

public class TableSource : UITableViewSource {

    private TableViewController controller;
    string CellIdentifier = "TableCell";

    public TableSource ()
    {

    }

    public TableSource (TableViewController controller)
    {
        this.controller = controller;
    }

    public override nint RowsInSection (UITableView tableview, nint section)
    {
        return 1;
    }

    public override UITableViewCell GetCell (UITableView tableView, NSIndexPath indexPath)
    {
        UITableViewCell cell = tableView.DequeueReusableCell (CellIdentifier);

        //if there are no cells to reuse, create a new one
        if (cell == null){
            cell = new UITableViewCell (UITableViewCellStyle.Default, CellIdentifier);
        }

        cell.TextLabel.Text = "test";

        return cell;
    }
}

I've noticed that the view controller (TableViewController) is never released. The table view controller has a reference to the data source, but the data source also has a reference to the table view controller.

With TableView.Source = new TableSource(); the view controller gets released, with TableView.Source = new TableSource(this); it's not.

How should this reference cycle be broken so that everything get released?

Edit:

Now I tried the WeakReference:

Through using a WeakReference the Dispose method is called, when the view controller is popped off the navigation stack.

In ViewDidLoad:

TableView.Source = new TableSource(new WeakReference<TableViewController> (this));

In the datasource:

private WeakReference<TableViewController> controller;

public TableSource (WeakReference<TableViewController> controller)
{
    this.controller = controller;
}

I built this into my real project, but how can I access my controller? I get the message

Type 'System.WeakReference' does not contain a definition for 'xxx' and no extension method 'xxx' of type 'System.WeakReference' could be found. Are you missing an assembly reference?

回答1:

You work with Xamarin, as I see? Have you tried WeakReference? https://msdn.microsoft.com/en-us/library/system.weakreference(v=vs.110).aspx

PS:

private WeakReference weakController; 

to set:

this.weakController = new WeakReference(controller); 

to get:

if (weakController.isAlive)
{
  TableViewController controller = weakController.Target as TableViewController;
}

回答2:

change

public partial class TableViewController : UITableViewController

to

public partial class TableViewController : UITableViewController, UITableViewSource

and in ViewDidLoad just do

self.TableView.Source = self;

the source property is a weak reference internally already so your have no problem of managing that. It is a convenience property to make the tbaleviewcontroller the delegate and datasource altogether. (Just like you would in native iOS)

回答3:

You can move the methods into the controller itself which would be less of a hassle than WeakReference. Then mark them with export attribute which then allows you to set the UITableView.WeakDataSource property to the controller itself.

[Export("tableView:numberOfRowsInSection:")]
public nint RowsInSection (UITableView tableview, nint section)

[Export("tableView:cellForRowAtIndexPath:")]
public UITableViewCell GetCell (UITableView tableView, NSIndexPath indexPath)

Once they are moved you can attach the datasource:

public override void ViewDidLoad ()
{
    TableView.WeakDataSource = this;
}