Binding of Button isEnabled Property to a Boolean Does Not Change When INotifyPropertyChanged Fires

Question

I have been attempting to successfully bind a Button's isEnabled property to a Boolean variable. After updating the Boolean, the Button's enabled state does not change. I used the helpful documentation from Microsoft for this subject to form my code, found here . Upon searching StackOverflow, I came across this article a regarding similar problem. It did not assist me in fixing this bug.

public class BackState : INotifyPropertyChanged
{
    public bool _isEnabled;
    public bool isEnabled
    {
        get
        {
            return _isEnabled;
        }

        set
        {
            if (value != _isEnabled)
            {
                _isEnabled = value;
                NotifyPropertyChanged("isEnabled");
                Debug.WriteLine("NotifyPropertyChanged was called successfully");
            }
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    private void NotifyPropertyChanged(string info)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(info));
    }

}

Snippet of XAML code:

<Grid DataContext="{Binding BackObject}" HorizontalAlignment="Stretch" Height="250" VerticalAlignment="Top">
    <Button x:FieldModifier="public" IsEnabled="{Binding isEnabled, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Click="Back_Click" x:Name="Back" Foreground="DarkGray" Content="&#xE76B;" FontFamily="Segoe MDL2 Assets" Background="#33FFFFFF" FontSize="20" Margin="40,70,0,133" />
</Grid>

My Boolean Change Function

public static void ChangeState(bool b)
{
    BackState bs = new BackState();
    if(b == true)
    {
        bs.isEnabled = true;
            Debug.WriteLine("Enabled Property");
    }else{
        bs.isEnabled = false;
            Debug.WriteLine("Disabled Property");
    }
}

And here is the BackObject definition

<local:BackState x:Key="BackObject"/>

In the GUI, the button constantly remains enabled. (Regardless of if ChangeState function is called) It should change disable/enable according to the called function.

Answer 1

In your ChangeState method you are creating a new BackState object, whereas this should be a property on the BackObject that you are setting as the DataContext . Instantiate a BackState that is a property on the BackObject , and bind to the isEnabled property of that object so that the xaml is told to listen for changes to that property.

<Grid DataContext="{Binding BackObject}" HorizontalAlignment="Stretch" Height="250" VerticalAlignment="Top">
    <Button x:FieldModifier="public" IsEnabled="{Binding yourPropertyWhcihIsBackState.isEnabled, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Click="Back_Click" x:Name="Back" Foreground="DarkGray" Content="&#xE76B;" FontFamily="Segoe MDL2 Assets" Background="#33FFFFFF" FontSize="20" Margin="40,70,0,133" />
</Grid>

and then in the method:

public static void ChangeState(bool b)
{
    if(b == true)
    {
        yourPropertyWhcihIsBackState.isEnabled = true;
            Debug.WriteLine("Enabled Property");
    }else{
        yourPropertyWhcihIsBackState.isEnabled = false;
        Debug.WriteLine("Disabled Property");
    }
}

But this won't work if you are ultimately making changes on an instance of an object to which the xaml is not bound. You seem to be creating a new instance of BackObject in your xaml, but it doesn't look like you have any way of accessing this object in your code. Consider setting up a ViewModel for accomplishing this. Take a look at mvvm light , it's a great mvvm (Model View ViewModel) framework.