wpf combobox binding is empty

Question

I am trying to work out wpf with some difficulties. This ComboBox seems a very basic issue but I can't have it populated even after reading all possible similar post.

The extra difficulty I think is that the ComboBox is defined in a resource, here is the resource code:

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                xmlns:s="clr-namespace:DiagramDesigner">

<ResourceDictionary.MergedDictionaries>
    <ResourceDictionary Source="Styles/Shared.xaml"/>
    <ResourceDictionary Source="Styles/ToolBar.xaml"/>
</ResourceDictionary.MergedDictionaries>

<ToolBar x:Key="MyToolbar" Height="120">

    <!--Languages-->
    <GroupBox Header="Localization" Style="{StaticResource ToolbarGroup}" Margin="3">
        <Grid>
            <ComboBox Height="23" HorizontalAlignment="Center" 
                      VerticalAlignment="Top"  Width="120"
                      ItemsSource="{Binding _langListString}" 
                        DisplayMemberPath="ValueString" 
                        SelectedValuePath="ValueString" 
                        SelectedValue="{Binding LangString}"
                      />
        </Grid>
    </GroupBox>

  </ToolBar>

My data object is defined as follow:

public partial class Window1 : Window
{

    List<ComboBoxItemString> _langListString = new List<ComboBoxItemString>();

    // Object to bind the combobox selections to.
    private ViewModelString _viewModelString = new ViewModelString();


    public Window1()
    {
        // Localization settings
        _langListString.Add(new ComboBoxItemString()); _langListString[0].ValueString = "en-GB";
        _langListString.Add(new ComboBoxItemString()); _langListString[1].ValueString = "fr-FR";
        _langListString.Add(new ComboBoxItemString()); _langListString[2].ValueString = "en-US";


        // Set the data context for this window.
        DataContext = _viewModelString;


        InitializeComponent();


    }

And the modelview:

/// This class provides us with an object to fill a ComboBox with
/// that can be bound to string fields in the binding object.
public class ComboBoxItemString
{
    public string ValueString { get; set; }
}


//______________________________________________________________________
//______________________________________________________________________
//______________________________________________________________________



/// Class used to bind the combobox selections to. Must implement 
/// INotifyPropertyChanged in order to get the data binding to 
/// work correctly.
public class ViewModelString : INotifyPropertyChanged
{
    /// Need a void constructor in order to use as an object element 
    /// in the XAML.
    public ViewModelString()
    {
    }

    private string _langString = "en-GB";

    /// String property used in binding examples.
    public string LangString
    {
        get { return _langString; }
        set
        {
            if (_langString != value)
            {
                _langString = value;
                NotifyPropertyChanged("LangString");
            }
        }
    }

    #region INotifyPropertyChanged Members

    /// Need to implement this interface in order to get data binding
    /// to work properly.
    private void NotifyPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    #endregion
}

I just don't know what to try else. Is anyone has an idea of what is going on, and why the combobox stays empty?

Many thanks.

Answer 1

you can just bind to public properties

 ItemsSource="{Binding _langListString}"

can not work because _langListString is not a public property

Answer 2

By my analysis the problem consist in your DataContext.

DataContext = _viewModelString;

If you give the viewModelString to the DataContext you have to have the _langListString >defined there, in order to the combobox know which item it is bound to.

This is what I would do:

1. Add List _langListString = new List(); to the >ModelView.
2. _langListString would be _viewModelString._langListString.add(Your Items) - be >carefull to instatiate the _langList when you create your _viewModelString object.

Then I think the rest would work.

---

Many thanks, I have the changes you've suggested but this combobox still stays empty :-(

The new modelview looks like this:

/// Class used to bind the combobox selections to. Must implement 
/// INotifyPropertyChanged in order to get the data binding to 
/// work correctly.
public class ViewModelString : INotifyPropertyChanged
{
    public List<ComboBoxItemString> _langListString {get;set;}
    /// Need a void constructor in order to use as an object element 
    /// in the XAML.
    public ViewModelString()
    {
        // Localization settings
        _langListString = new List<ComboBoxItemString>();
        ComboBoxItemString c;
        c = new ComboBoxItemString(); c.ValueString = "en-GB"; _langListString.Add(c);
        c = new ComboBoxItemString(); c.ValueString = "fr-FR"; _langListString.Add(c);
        c = new ComboBoxItemString(); c.ValueString = "en-US"; _langListString.Add(c); 
    }

    private string _langString = "en-GB";

    /// String property used in binding examples.
    public string LangString
    {
        get { return _langString; }
        set
        {
            if (_langString != value)
            {
                _langString = value;
                NotifyPropertyChanged("LangString");
            }
        }
    }

    #region INotifyPropertyChanged Members

    /// Need to implement this interface in order to get data binding
    /// to work properly.
    private void NotifyPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    #endregion
}

The data object:

  // Object to bind the combobox selections to.
    private ViewModelString _viewModelString;

    public Window1()
    {
        // Set the data context for this window.
        _viewModelString = new ViewModelString();
        DataContext = _viewModelString;

        InitializeComponent();
    }

And I have tried all possible combination in the combobox (_langListString, _viewModelString._langListString, _viewModelString) it just doesn't work:

<ComboBox Height="23" HorizontalAlignment="Center" 
                      VerticalAlignment="Top"  Width="120"
                      ItemsSource="{Binding _langListString}" 
                        DisplayMemberPath="ValueString" 
                        SelectedValuePath="ValueString" 
                        SelectedValue="{Binding LangString}"
                      />

I tend to think that this xaml is making things really complicated without possibility of debugging. Is anyone can help???