WPF application is not updating its Window.Left property at runtime

Question

I am trying to get my wpf application to take up my right-side monitor when it loads. My approach involves me creating a property that stores the screen width value (as a double) and then bind this to the Window.Left property. But no matter what I do the application window doesn't move to my right monitor.

here is my xaml

<Window x:Class="Foo.FooView"
        .. declarations
        Title="{Binding Title}" 
    Left="{Binding ScreenOffset, Mode=OneWayToSource, UpdateSourceTrigger=PropertyChanged}"
        Height="800"
    Width="1920"
        SnapsToDevicePixels="True">

in my View Model:

    public double ScreenOffset
    {
        get
        {
            return _screenOffset;
        }
        set
        {
            if (_screenOffset != value)
            {
                _screenOffset = value;
                RaisePropertyChanged(nameof(ScreenOffset));
            }
        }
    }
    private double _screenOffset = 0.0;

    public FooViewModel()
    {
        ScreenOffset = Application.Current.MainWindow.Width + defaultOffset; 
        //Application.Current.MainWindow.Width = 1920
        //defaultOffset = 10.0
    }

My data binding works with other controls in my application. The only binding that doesn't seem to work is just the Left property. Can anyone see what I am doing wrong? Many thanks in advance.

Answer 1

First I want to thank @PavelAnikhouski and @Miguel Carreira for your time and effort to help me figure this out. So, my problem had nothing to do with the fact that I wasn't setting up my binding properly. My issue was that my WindowState was defaulted to Maximized from the start. This site helped me understand that too. I solved my issue by binding my WindowState and defaulting it to Normal. I then set the new Left value and bind it to the property, and finally I changed my WindowState to Maximized.

//setting up the dashboard window position, first
//the WindowState has to be set to Normal
WindowState = WindowState.Normal;

//second, we get the offset value based on the configuration settings
ScreenOffset = Application.Current.MainWindow.Width + defaultOffset;

//third, we set the desired WindowState to Maximized
WindowState = WindowState.Maximized;

Now my window appears in its desired location. Thank you again.

Answer 2

Can you try to put the following code in your view model:

    public event PropertyChangedEventHandler PropertyChanged;

    private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    public double ScreenOffset
    {
        get
        {
            return _screenOffset;
        }
        set
        {
            if (_screenOffset != value)
            {
                _screenOffset = value;
                NotifyPropertyChanged();
            }
        }
    }