xaml binding not working as expected

Question

I have created a simple credo (create, review, edit, delete, overview) wpf application for cars to learn about c# and have run into an issue. When either adding or editing an item to my observable collection, I want to allow the user to be able to browse the computer for a picture associated with the car. I originally had accomplished this in code behind with the following:

namespace CarApp
{
public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    /// <summary>
    /// Open a browser window when the user clicks on the 'browse' button
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    private void Add_Browse_Button_Click(object sender, RoutedEventArgs e)
    {
        //send path to textbox
        AddPicturePath.Text = this.Browse();
    }

    ///// <summary>
    ///// Open a browser window when the user clicks on the 'browse' button
    ///// </summary>
    ///// <param name="sender"></param>
    ///// <param name="e"></param>
    private void Edit_Browse_Button_Click(object sender, RoutedEventArgs e)
    {
        //send path to textbox
        EditPicturePath.Text = this.Browse();
    }

    /// <summary>
    /// Open browser window and return user selection
    /// </summary>
    /// <returns>filename</returns>
    private string Browse()
    {
        //open browser window
        Microsoft.Win32.OpenFileDialog dlg = new Microsoft.Win32.OpenFileDialog();

        //search only for .png files
        dlg.DefaultExt = ".png";

        //show browser
        dlg.ShowDialog();

        return dlg.FileName;
    }
}
}

This worked perfectly but then I was requested to remove all code behind (which seemed fine to be because this is purely a UI element, tell me if I'm wrong) from the application. So I moved the code into an ICommand:

namespace CarApp.Commands
{
public class BrowseCommand : ICommand
{
    public bool CanExecute(object parameter)
    {
        return true;
    }

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

    public void Execute(object parameter)
    {
        Car param = parameter as Car;

        try
        {
            //open browser window
            Microsoft.Win32.OpenFileDialog dlg = new Microsoft.Win32.OpenFileDialog();

            //search only for .png files
            dlg.DefaultExt = ".png";

            //show browser
            dlg.ShowDialog();

            //send path to textbox
            param.PicturePath = dlg.FileName;
        }
        catch (NullReferenceException)
        {
            Console.Write("Param is null in browse");

        }

    }
}
}

Now when I run the application, the path does not show up in the textbox, when when I click the "add to list" button, the item is added displaying the proper image. It seems as though the textbox is not updating, even though I have INotification implemented. Am I missing something obvious? Here is relevant the xaml code:

<Button Width="75"
    Height="23"
    Margin="10,0,0,0"
    HorizontalAlignment="Left"
    Command="{Binding BrowseCommand}"
    CommandParameter="{Binding NewCar}"
    Content="Browse" />

and

<TextBox x:Name="AddPicturePath"
        Width="200"
        Height="23"
        Margin="10,0,0,0"
        HorizontalAlignment="Left"
        ScrollViewer.VerticalScrollBarVisibility="Auto"
        Text="{Binding NewCar.PicturePath,
                    UpdateSourceTrigger=PropertyChanged}"
        TextWrapping="Wrap" />

Answer 1

If I understand this correctly, you are binding to NewCar.PicturePath but only NewCar is changing. When you Notify of property changed, I am guessing you only notify that the NewCar object is changing (not the PicturePath). Try this; within the NewCar setter, after setting _NewCar = value, also update _NewCar.PicturePath and assuming PicturePath also is notifying properly, it should update properly and also give you some insight as to how the binding is working... Hope this helps!