Question

I have never come across this issue but most recently I noticed that a two way binding to a property doesn’t work if the property resides in a Singleton.

What I mean is that the ‘other’ CheckBox never updates its value.

Any ideas on how to make it work?
Thanks in advance!

Singleton.cs

public class Singleton : INotifyPropertyChanged
{
    private bool panelClosed;

    static Singleton()
    {
        Instance = new Singleton();
    }

    public event PropertyChangedEventHandler PropertyChanged;

    public static Singleton Instance { get; private set; }

    public bool PanelClosed
    {
        get
        {
            return this.panelClosed;
        }

        set
        {
            this.panelClosed = value;
            this.NotifyPropertyChanged("PanelClosed");
        }
    }

    private void NotifyPropertyChanged(string info)
    {
        if (this.PropertyChanged != null)
        {
            this.PropertyChanged(null, new PropertyChangedEventArgs(info));
        }
    }
}

XAML:

<CheckBox 
    Content="Check/Uncheck me" 
    Height="16" Name="checkBox1" 
    IsChecked="{Binding Source={x:Static local:Singleton.Instance}, Path=PanelClosed, 
                UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"/>

<CheckBox 
    Content="Sanity Check" 
    Height="16" Name="checkBox2" 
    IsChecked="{Binding Source={x:Static local:Singleton.Instance}, Path=PanelClosed, 
                UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}" />

Answer 1

This had me confused for a bit, but it’s a simple fix. There’s no problem using a singleton.

Change

this.PropertyChanged(null, new PropertyChangedEventArgs(info));

to

this.PropertyChanged(this, new PropertyChangedEventArgs(info));