Question

In my application, I am generating a datagrid programatically and binding it with a list. I am able to see the data in the datagrid but when I edit the cell, the underlying item in the list does not get updated. Here is the code

Window dateChangeWindow = new Window();
dateChangeWindow.WindowStartupLocation = WindowStartupLocation.CenterOwner;
dateChangeWindow.Owner = Application.Current.MainWindow;
dateChangeWindow.SizeToContent = SizeToContent.WidthAndHeight;
dateChangeWindow.Title = "Date Change";

StackPanel stackPanel = new StackPanel();
stackPanel.Orientation = Orientation.Vertical;

DataGrid requestGrid = new DataGrid();
requestGrid.CanUserResizeColumns = false;
requestGrid.CanUserResizeRows = false;
requestGrid.CanUserReorderColumns = false;
requestGrid.CanUserSortColumns = true;
requestGrid.AutoGenerateColumns = false;

DataGridTextColumn requestIdColumn = new DataGridTextColumn();
requestIdColumn.Header = "Request Id";
Binding idBinding = new Binding("RequestId");
idBinding.Mode = BindingMode.OneWay;
requestIdColumn.Binding = idBinding;
requestGrid.Columns.Add(requestIdColumn);

DataGridTemplateColumn startDateColumn = new DataGridTemplateColumn();
startDateColumn.Header = "Start Date";
Binding startDateBinding = new Binding("StartDate");
startDateBinding.Mode = BindingMode.TwoWay;
FrameworkElementFactory startDateFactory = new FrameworkElementFactory(typeof(DatePicker));
startDateFactory.SetBinding(DatePicker.SelectedDateProperty, startDateBinding);
DataTemplate startDateTemplate = new DataTemplate();
startDateTemplate.VisualTree = startDateFactory;
startDateColumn.CellTemplate = startDateTemplate;
startDateColumn.CellEditingTemplate = startDateTemplate;
requestGrid.Columns.Add(startDateColumn);

DataGridTemplateColumn endDateColumn = new DataGridTemplateColumn();
endDateColumn.Header = "End Date";
Binding endDateBinding = new Binding("EndDate");
endDateBinding.Mode = BindingMode.TwoWay;
FrameworkElementFactory endDateFactory = new FrameworkElementFactory(typeof(DatePicker));
endDateFactory.SetBinding(DatePicker.SelectedDateProperty, endDateBinding);
DataTemplate endDateTemplate = new DataTemplate();
endDateTemplate.VisualTree = endDateFactory;
endDateColumn.CellTemplate = endDateTemplate;
endDateColumn.CellEditingTemplate = endDateTemplate;
requestGrid.Columns.Add(endDateColumn);

requestGrid.ItemsSource = requestList;
requestGrid.Margin = new Thickness(0, 10, 0, 0);
requestGrid.HorizontalAlignment = HorizontalAlignment.Center;

stackPanel.Children.Add(requestGrid);

Button changeDoneBtn = new Button();
changeDoneBtn.Content = "Submit";
changeDoneBtn.Click += new RoutedEventHandler(changeDone_Click);
changeDoneBtn.Margin = new Thickness(0, 20, 0, 10);
changeDoneBtn.HorizontalAlignment = HorizontalAlignment.Center;

stackPanel.Children.Add(changeDoneBtn);

dateChangeWindow.Content = stackPanel;
dateChangeWindow.ShowDialog();

The ItemsSource requestList is populated before the window creation. It is declared as

IList<DateChangeWrapper> requestList = new List<DateChangeWrapper>();

And the DateChangeWrapper class looks like this

public class DateChangeWrapper : INotifyPropertyChanged
{
    public DateChangeWrapper(ResponseWrapper responseWrapper)
    {
        RequestId = responseWrapper.RequestId;
        ParentRequestId = responseWrapper.ParentRequestId;
        StartDate = responseWrapper.StartDate;
        EndDate = responseWrapper.EndDate;
    }

    private DateTime startDate;
    private DateTime endDate;

    public int RequestId { get; private set; }
    public int ParentRequestId { get; private set; }

    public DateTime StartDate
    {
        get { return startDate; }
        set
        {
            startDate = value;
            OnPropertyChanged("StartDate");
        }
    }

    public DateTime EndDate
    {
        get { return endDate; }
        set
        {
            endDate = value;
            OnPropertyChanged("EndDate");
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;  

    private void OnPropertyChanged(string propertyName)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
        {
            var e = new PropertyChangedEventArgs(propertyName);
            handler(this, e);
        }
    }
}

As you can see from the code, I have two columns StartDate and EndDate which are displayed as DatePickers . When I debug the code, the point where window.ShowDialog is called, I see the get accessor of the Dates getting called. But when I change the value in the datepicker, the setter does not get called and my list still has the old value.

Please help me

Answer 1

The problem was that the changed value was not getting updated back to the underlying source because of UpdateSourceTrigger. By default, this has the value of LostFocus. I changed it to PropertyChanged and it worked ! 🙂

I added the following line of code to my binding

startDateBinding.UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;

and similarly for EndDate