Mvvm Light message recipient action being garbage collected

问题

My wpf application has child windows that popup to show views to the user. The child windows are closed by executing CloseCommand on the window's viewmodel, which sends a CloseWindowMessage using itself as the token.

This is the viewmodel used:

public class ChildWindowViewModel : ViewModel
{
    ICommand _closeCommand;
    public ICommand CloseCommand
    {
        get
        {
            if (_closeCommand == null)
                _closeCommand = new RelayCommand(DoClose);
            return _closeCommand;
        }
    }

    public void DoClose()
    {
        System.GC.Collect();
        System.GC.WaitForPendingFinalizers();
        Messenger.Default.Send(new CloseWindowMessage(),this);
    }
}

This is the method that shows windows:

protected void ShowWpfWindow(Window wpfWindow)
{
    var dc = wpfWindow.DataContext as ChildWindowViewModel;
    if (dc == null)
        throw new ArgumentOutOfRangeException();

    Action<CloseWindowMessage> action = (x) => 
    {
        wpfWindow.Close();
    };
    Messenger.Default.Register(wpfWindow, dc, action);

    wpfWindow.Owner = MainWindow.Single;
    wpfWindow.ShowInTaskbar = false;
    wpfWindow.Show();
}

I have added the calls to GC.Collect() and GC.WaitForPendingFinalizers() for debugging purposes. These seem to cause the variable Action<CloseWindowMessage> action to be garbage collected.

If I make Action<CloseWindowMessage> action a field on the containing class:

Action<CloseWindowMessage> action;
protected void ShowWpfWindow(Window wpfWindow)
{
    var dc = wpfWindow.DataContext as ChildWindowViewModel;
    if (dc == null)
        throw new ArgumentOutOfRangeException();

    action = (x) => 
    {
        wpfWindow.Close();
    };
    Messenger.Default.Register(wpfWindow, dc, action);

    wpfWindow.Owner = MainWindow.Single;
    wpfWindow.ShowInTaskbar = false;
    wpfWindow.Show();
}

The code works. I assume that the messenger maintains only a weak reference to the action, so that once execution passes out of ShowWpfWindow the action may be garbage collected. By setting the action as a field on the class, I am tying its lifetime to that of its containing object. However, I don't want to do this as the lifetime of the containing object may be less than wpfWindow.

What sort of pattern should I adopt to ensure that the close action is not disposed?

来源：https://stackoverflow.com/questions/22536399/mvvm-light-message-recipient-action-being-garbage-collected

标签

wpf

mvvm

mvvm-light