ICommand binding causing UI memory leak in WPF application

Question

I\'m building a WPF app that connects to a SQL Server database using LINQ to SQL.

The main window of the app contains a ListView containing a series of

Answer 1

The CanExecuteChanged event handler is likely implicated in the leak.

WPF expects ICommand implementations to use weak references to the event handlers. You're using a normal .NET event which uses strong references, which can cause this leak.

The way you are creating the ParameterlessCommand instance seems to imply that CanExecute will always be true, and you don't need the event at all. Are you actually firing the event anywhere, or is OnCanExecuteChanged unused code?

If not, replace the event definition with:

public event EventHandler CanExecuteChanged { add {} remove {} }

This way the event does not store any handlers, and the view model avoids having a strong reference to the UI elements.

If you need to raise the event, the easiest solution is to use CommandManager.RequerySuggested, which matches the weak event semantics expected for ICommand:

public event EventHandler CanExecuteChanged {
    add {
        CommandManager.RequerySuggested += value;
    }
    remove {
        CommandManager.RequerySuggested -= value;
    }
}

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Another thing you should do is implement INotifyPropertyChanged in your view model (if you haven't done so already), and use that instead of having individual NameChanged etc. events for each property. This is because the logic in WPF dealing with the individual properties causes memory leaks when there is a reference from the view model back to the UI elements: http://support.microsoft.com/kb/938416

AFAIK you need to implement INotifyPropertyChanged even if you don't actually have any change events.

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My guess is that fixing either of these two problems will make the leak disappear: the incorrectly implemented CanExecuteChanged causes a strong reference from view model to view, which is exactly the circumstance under which the lack of INotifyPropertyChanged causes a leak.

But it's a good idea to fix both issues; not just one of them.