ListBox ItemsSource Doesn't Update

Question

I am facing a ListBox's ItemsSource related issue. I am implementing MVVM with WPF MVVM toolkit version 0.1.

I set one ListBox itemSource to update when a user double clicks on some other element (I handled the event in the code behind and executed the command there, since binding a command to specific events are not supported). At this point through the execution of the command a new ObservableCollection of items get generated and the ListBox's ItemsSource is intended to get updated accordingly. But it is not happening at the moment. ListBox does not update dynamically. What can be the problem? I am attaching relvent code for your reference.

XAML:

List of items which is doubled click to generate the next list:

<ListBox Height="162" HorizontalAlignment="Left" Margin="10,38,0,0" Name="tablesViewList" VerticalAlignment="Top" Width="144" Background="Transparent" BorderBrush="#20EEE2E2" BorderThickness="5" Foreground="White" ItemsSource="{Binding Path=Tables}" SelectedValue="{Binding TableNameSelected, Mode=OneWayToSource}" MouseDoubleClick="tablesViewList_MouseDoubleClick"/>

Second list of items which currently does not get updated:

 <ListBox Height="153" HorizontalAlignment="Left" Margin="10,233,0,0" Name="columnList" VerticalAlignment="Top" Width="144" Background="Transparent" BorderBrush="#20EEE2E2" BorderThickness="5" Foreground="White" ItemsSource="{Binding Path=Columns, Mode=OneWay}" DisplayMemberPath="ColumnDiscriptor"></ListBox>

Code Behind:

    private void tablesViewList_MouseDoubleClick(object sender, MouseButtonEventArgs e)
    {
        MainViewModel currentViewModel = (MainViewModel)DataContext;

        MessageBox.Show("Before event command is executed");
        ICommand command = currentViewModel.PopulateColumns;
        command.Execute(null);

        MessageBox.Show(currentViewModel.TableNameSelected);
        //command.Execute();
    }

View Model:

namespace QueryBuilderMVVM.ViewModels
{
//delegate void Del();

public class MainViewModel : ViewModelBase
{
    private DelegateCommand exitCommand;

    #region Constructor

    private ColumnsModel _columns; 

    public TablesModel Tables { get; set; }
    public ControllersModel Operators { get; set; }
    public ColumnsModel Columns {

        get { return _columns; }
        set {
            _columns = value;
            OnPropertyChanged("Columns");
        } 
    }

    public string TableNameSelected{get; set;}



    public MainViewModel()
    {
        Tables = TablesModel.Current;
        Operators = ControllersModel.Current;
        Columns = ColumnsModel.ListOfColumns;
    }

    #endregion

    public ICommand ExitCommand
    {
        get
        {
            if (exitCommand == null)
            {
                exitCommand = new DelegateCommand(Exit);
            }
            return exitCommand;
        }
    }

    private void Exit()
    {
        Application.Current.Shutdown();
    }






    //Del columnsPopulateDelegate = new MainViewModel().GetColumns;


    //Method to be assigned to the delegate
    //Creates an object of type ColumnsModel
    private void GetColumns() { 

         ColumnsModel.TableNameParam = TableNameSelected;
        Columns = ColumnsModel.ListOfColumns;
    }



    private ICommand _PopulateColumns;
    public ICommand PopulateColumns
    {
        get {

            if (_PopulateColumns == null) {

                _PopulateColumns = new DelegateCommand(GetColumns); // an action of type method is passed
            }

            return _PopulateColumns;
        }

    }


}

}

Model:

public class ColumnsModel : ObservableCollection<VisualQueryObject>
{

    private DataSourceMetaDataRetriever dataSourceTableMetadataObject;// base object to retrieve sql data
    private static ColumnsModel listOfColumns = null;
    private static object _threadLock = new Object();
    private static string tableNameParam = null;

    public static string TableNameParam
    {
        get { return ColumnsModel.tableNameParam; }
        set { ColumnsModel.tableNameParam = value; }
    }

    public static ColumnsModel ListOfColumns
    {
        get
        {
            lock (_threadLock)
                if (tableNameParam != null)
                    listOfColumns = new ColumnsModel(tableNameParam);

            return listOfColumns;
        }

    }


    public ColumnsModel(string tableName)
    {
        ColumnsModel.tableNameParam = tableName;
        Clear();

        try
        {
            dataSourceTableMetadataObject = new DataSourceMetaDataRetriever();

            List<ColumnDescriptionObject> columnsInTable = new List<ColumnDescriptionObject>();

            columnsInTable = dataSourceTableMetadataObject.getDataTableSchema("Provider=SQLOLEDB;Data Source=.;Integrated Security=SSPI;Initial Catalog=LogiwizUser", ColumnsModel.tableNameParam);

            //List<String> listOfTables = dataSourceTableMetadataObject.getDataBaseSchema("Provider=SQLOLEDB;Data Source=.;Integrated Security=SSPI;Initial Catalog=LogiwizUser");
            //List<String> listOfTables = dsm.getDataBaseSchema("G:/mytestexcel.xlsx", true);

            //ObservableCollection<VisualQueryObject> columnVisualQueryObjects = new ObservableCollection<VisualQueryObject>();

            foreach (ColumnDescriptionObject columnDescription in columnsInTable)
            {
                VisualQueryObject columnVisual = new VisualQueryObject();
                columnVisual.ColumnDiscriptor = columnDescription;
                columnVisual.LabelType = "column";

                Add(columnVisual);
            }



        }
        catch (QueryBuilderException ex)
        {
            /* Label exceptionLabel = new Label();
             exceptionLabel.Foreground = Brushes.White;
             exceptionLabel.Content = ex.ExceptionMessage;
             grid1.Children.Add(exceptionLabel);*/

        }
    }

}

Any help is greatly appreciated. Thanks in advance.

Answer 1

The setter of property Columns should raise a PropertyChanged event. Implement INotifyPropertyChanged to do so : MSDN INotifyPropertyChanged

I guess MVVM Toolkit provides a way of doing so easily (perhaps ViewModelBase already implement the interface ...).

EDIT : Implementing INotifyPropertyChanged is not enough, you have to raise the event created by INotifyPropertyChanged. You property should look something like this :

private ColumnsModel _columns;
public ColumnsModel Columns 
{ 
  get { return _columns; } 
  set 
  { 
    _columns = value; 
    PropertyChanged("Columns"); 
  }
}

Answer 2

use an observableCollection<T> instead of a List<T>

MSDN DOC:

WPF provides the ObservableCollection class, which is a built-in implementation of a data collection that exposes the INotifyCollectionChanged interface. Note that to fully support transferring data values from source objects to targets, each object in your collection that supports bindable properties must also implement the INotifyPropertyChanged interface. For more information, see Binding Sources Overview.