wpf combobox binding is empty - wpf

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:
Add List _langListString = new List(); to the >ModelView.
_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???