silverlight 4.0 drodown keypress

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• Tuesday, June 07, 2011 1:27 PM

   

   
  

  0

  Hi All

  I got a workaround to implement this feature using the Behaviour.

  Xaml

  xmlns:KBS ="clr-namespace:X.ViewModel.Service.Common"

  <ComboBox  Name="cbEngineer" ItemsSource="{Binding Path=EmployeeCollection,Mode=TwoWay}" SelectedValue="{Binding Path=Engineer,Mode=TwoWay}"  SelectedItem="{Binding Engineer,Mode=TwoWay,NotifyOnValidationError=True,ValidatesOnDataErrors=True}" DisplayMemberPath="Value" TabIndex="0" Grid.Column="1" Grid.Row="0" Width="120">
                                          <i:Interaction.Behaviors>
                                                                <KBS:KeyboardSelectionBehavior/>
                                                      </i:Interaction.Behaviors>

  </ComboBox>

  Behaviour

  namespace X.ViewModel.Service.Common
  {
      /// <summary>
      /// This behavior can be attached to a ListBox or ComboBox to
      /// add keyboard selection
      /// </summary>
      public class KeyboardSelectionBehavior : Behavior<Selector> {

          private bool _bound;

          /// <summary>
          /// Gets or sets the Path used to select the text
          /// </summary>
          public string SelectionMemberPath { get; set; }

          public KeyboardSelectionBehavior() { }

          /// <summary>
          /// Attaches to the specified object: subscribe on KeyDown event
          /// </summary>
          protected override void OnAttached() {
              base.OnAttached();
              this.AssociatedObject.KeyDown += DoKeyDown;

              if (this.AssociatedObject is ComboBox) {
                  ((ComboBox)this.AssociatedObject).DropDownOpened += new EventHandler(KeyboardSelectionBehavior_DropDownOpened);
              }
          }

          void KeyboardSelectionBehavior_DropDownOpened(object sender, EventArgs e) {
              System.Windows.Deployment.Current.Dispatcher.BeginInvoke(this.BindBehaviorToStackPanel);
          }

          void BindBehaviorToStackPanel() {
              var hoster = (((ComboBox)this.AssociatedObject).GetItemsHost() as StackPanel);
              if (_bound == false && hoster != null) {
                  _bound = true;
                  hoster.KeyDown += DoKeyDown;
              }
          }

          void DoKeyDown(object sender, KeyEventArgs e) {
              // Create a list of strings and indexes
              int index = 0;
              IEnumerable<Item> list = null;
              var path = SelectionMemberPath ??
                  this.AssociatedObject.DisplayMemberPath;
              var evaluator = new BindingEvaluator();
              if (path != null) {
                  list = this.AssociatedObject.Items.OfType<object>()
                      .Select(item => {
                          // retrieve the value using the supplied Path
                          var binding = new Binding();
                          binding.Path = new PropertyPath(path);
                          binding.Source = item;

                          BindingOperations.SetBinding(evaluator,
                              BindingEvaluator.TargetProperty, binding);
                          var value = evaluator.Target;

                          return new Item {
                              Index = index++,
                              Text = Convert.ToString(value)
                          };
                      });
              } else {
                  list = this.AssociatedObject.Items.OfType<ListBoxItem>()
                      .Select(item => new Item {
                          Index = index++,
                          Text = Convert.ToString(item.Content)
                      });
              }
              // Sort the list starting at next selectedIndex to the end and
              // then from the beginning
              list = list.OrderBy(item => item.Index <=
                  this.AssociatedObject.SelectedIndex ?
                  item.Index + this.AssociatedObject.Items.Count : item.Index);

              // Find first starting with
              var text = e.Key.ToString();
              var first = list.FirstOrDefault(item => item.Text.StartsWith(text,
                  StringComparison.InvariantCultureIgnoreCase));
              if (first != null) {
                  // found
                  this.AssociatedObject.SelectedIndex = first.Index;
              }
          }

          /// <summary>
          /// Helper class
          /// </summary>
          private class Item {
              public int Index;
              public string Text;
          }

          /// <summary>
          /// Helper class used for property path value retrieval
          /// </summary>
          private class BindingEvaluator : FrameworkElement {

              public static readonly DependencyProperty TargetProperty =
                  DependencyProperty.Register(
                      "Target",
                      typeof(object),
                      typeof(BindingEvaluator), null);

              public object Target {
                  get { return GetValue(TargetProperty); }
                  set { SetValue(TargetProperty, value); }
              }
          }

   

      }
  }

  • Marked As Answer by Anbu Varadhan Wednesday, June 08, 2011 10:16 AM
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