/// 
    /// AutoCompleteComboBox    /// 
    public class AutoCompleteComboBox : ComboBox    {        #region DependencyProperty        public string WaterMark        {            get { return (string)GetValue(WaterMarkProperty); }            set { SetValue(WaterMarkProperty, value); }        }        // Using a DependencyProperty as the backing store for WaterMark.  This enables animation, styling, binding, etc...        public static readonly DependencyProperty WaterMarkProperty =            DependencyProperty.Register("WaterMark", typeof(string), typeof(AutoCompleteComboBox), new PropertyMetadata(null, new PropertyChangedCallback(OnWaterMarkChanged)));        public bool? IsNull        {            get { return (bool?)GetValue(IsNullProperty); }            set { SetValue(IsNullProperty, value); }        }        // Using a DependencyProperty as the backing store for IsNull.  This enables animation, styling, binding, etc...        public static readonly DependencyProperty IsNullProperty =            DependencyProperty.Register("IsNull", typeof(bool?), typeof(AutoCompleteComboBox), new PropertyMetadata(null));        public bool? SetFocuse        {            get { return (bool?)GetValue(SetFocuseProperty); }            set { SetValue(SetFocuseProperty, value); }        }        // Using a DependencyProperty as the backing store for SetFocuse.  This enables animation, styling, binding, etc...        public static readonly DependencyProperty SetFocuseProperty =            DependencyProperty.Register("SetFocuse", typeof(bool?), typeof(AutoCompleteComboBox), new PropertyMetadata(null, new PropertyChangedCallback(OnSetFocuseChanged)));        public bool IsAllowNull        {            get { return (bool)GetValue(IsAllowNullProperty); }            set { SetValue(IsAllowNullProperty, value); }        }        // Using a DependencyProperty as the backing store for IsAllowNull.  This enables animation, styling, binding, etc...        public static readonly DependencyProperty IsAllowNullProperty =            DependencyProperty.Register("IsAllowNull", typeof(bool), typeof(AutoCompleteComboBox), new PropertyMetadata(true, new PropertyChangedCallback(OnIsAllowNullChanged)));        private static void OnIsAllowNullChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)        {                  }                        #endregion        #region Event        private static void OnWaterMarkChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)        {        }        private static void OnSetFocuseChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)        {            AutoCompleteComboBox wm = obj as AutoCompleteComboBox;            if (e.NewValue != null && wm.EditableTextBox != null)            {                if ((bool)e.NewValue == true && wm.EditableTextBox.IsFocused != true)                {                    wm.EditableTextBox.Focus();                }            }        }        public IList DataSource        {            get { return (IList)GetValue(DataSourceProperty); }            set { SetValue(DataSourceProperty, value); }        }        // Using a DependencyProperty as the backing store for DataSource.  This enables animation, styling, binding, etc...        public static readonly DependencyProperty DataSourceProperty =            DependencyProperty.Register("DataSource", typeof(IList), typeof(AutoCompleteComboBox), new UIPropertyMetadata(null, new PropertyChangedCallback(OnDataSourceChanged)));        private static void OnDataSourceChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)        {            AutoCompleteComboBox a = d as AutoCompleteComboBox;            //if (a.IsAllowNull)            //{
                     a.Items.Clear();                if (a.DataSource != null)                {                                        Type b = null;                    foreach (var item in a.DataSource)                    {                        if (b == null)                        {                            b = item.GetType();                            object o = Activator.CreateInstance(b);                            //o.GetType().GetProperty(a.DisplayMemberPath).SetValue(o, "----Select----", null);                            a.Items.Add(o);                        }                        a.Items.Add(item);                    }                               }                else                {                    a.ItemsSource = null;                }             //}                   }        protected override void OnDropDownOpened(EventArgs e)        {            base.OnDropDownOpened(e);            if (this.HasItems)            {                this.Items[0].GetType().GetProperty(this.DisplayMemberPath).SetValue(this.Items[0], "----Select----", null);            }                   }        protected override void OnDropDownClosed(EventArgs e)        {            base.OnDropDownClosed(e);            if (this.SelectedIndex == 0)            {                //this.SelectedItem = null;                //this.SelectedItem = null;                //this.Text = null;                //this.SelectedValue = null;                this.SelectedIndex = -1;            }        }        public override void OnApplyTemplate()        {            base.OnApplyTemplate();            //load the text box control            if (this.EditableTextBox != null && this.MyWaterMarkTextBlock != null)            {                if (SetFocuse == true)                {                    if (!this.EditableTextBox.IsFocused)                    {                        this.EditableTextBox.Focus();                    }                }                this.EditableTextBox.TextChanged += new TextChangedEventHandler(EditableTextBox_TextChanged);                this.EditableTextBox.GotFocus += EditableTextBox_GotFocus;                this.Loaded += AutoCompleteComboBox_Loaded;            }        }                void AutoCompleteComboBox_Loaded(object sender, RoutedEventArgs e)        {                       if (string.IsNullOrWhiteSpace(this.Text))            {                this.MyWaterMarkTextBlock.Visibility = Visibility.Visible;                //this.MyWaterMarkTextBlock.Text = WaterMark;                this.IsNull = false;            }            else            {                this.MyWaterMarkTextBlock.Visibility = Visibility.Collapsed;                //this.MyWaterMarkTextBlock.Text = WaterMark;                this.IsNull = true;            }            try            {                //if (this.HasItems)                //{                //    this.Items[0].GetType().GetProperty(this.DisplayMemberPath).SetValue(this.Items[0], "----Select----", null);                //}                //if (!this.IsAllowNull)                //{                //    this.EditableTextBox.IsEnabled = false;                //}            }            catch (Exception)            {                                           }                   }        void EditableTextBox_GotFocus(object sender, RoutedEventArgs e)        {            if (this.MyWaterMarkTextBlock.Visibility == Visibility.Visible)            {                // this.Text = null;                this.MyWaterMarkTextBlock.Visibility = Visibility.Collapsed;                //this.MyWaterMarkTextBlock.Text = WaterMark;            }            this.IsDropDownOpen = true;        }        protected override void OnSelectionChanged(SelectionChangedEventArgs e)        {           base.OnSelectionChanged(e);                       if (this.SelectedIndex == 0)                {                    this.SelectedIndex = -1;                }                    }        void EditableTextBox_TextChanged(object sender, TextChangedEventArgs e)        {            if (this.EditableTextBox.IsFocused && this.IsDropDownOpen == false)            {                this.IsDropDownOpen = true;            }            if (string.IsNullOrWhiteSpace(this.Text))            {                if (!this.EditableTextBox.IsFocused)                {                    this.MyWaterMarkTextBlock.Visibility = Visibility.Visible;                    // this.MyWaterMarkTextBlock.Text = WaterMark;                }                this.IsNull = false;            }            else            {                this.IsNull = true;                this.MyWaterMarkTextBlock.Visibility = Visibility.Collapsed;                // this.MyWaterMarkTextBlock.Text = WaterMark;            }        }                void SimpleAutoCompleteComboBox_LostFocus(object sender, RoutedEventArgs e)        {            this.IsDropDownOpen = false;            // to prevent misunderstanding that user has entered some information            if (this.SelectedIndex == -1 || this.SelectedIndex == 0)            {                this.Text = null;                this.SelectedItem = null;                this.SelectedValue = null;                this.MyWaterMarkTextBlock.Visibility = Visibility.Visible;                this.IsNull = false;                // this.MyWaterMarkTextBlock.Text = WaterMark;                  }            // syncronize text            else            {                this.Text = this.SelectedText;                this.IsNull = true;            }            // release timer resources            try            {                this.EditableTextBox.CaretIndex = 0;            }            catch { }        }            #endregion        #region Construtor        static AutoCompleteComboBox()        {            DefaultStyleKeyProperty.OverrideMetadata(typeof(AutoCompleteComboBox), new FrameworkPropertyMetadata(typeof(AutoCompleteComboBox)));        }        public AutoCompleteComboBox()        {            this.StaysOpenOnEdit = true;            this.IsEditable = true;            this.IsTextSearchEnabled = true;            this.LostFocus += SimpleAutoCompleteComboBox_LostFocus;            this.IsAllowNull = true;        }        #endregion        protected override void OnItemsSourceChanged(System.Collections.IEnumerable oldValue, System.Collections.IEnumerable newValue)        {            base.OnItemsSourceChanged(oldValue, newValue);        }        #region property        /// 
        /// Gets the waterMark  .        /// 
        protected TextBlock MyWaterMarkTextBlock        {            get            {                return base.GetTemplateChild("PART_MyWaterMarkTextBlock") as TextBlock;            }        }        /// 
        /// Gets the text box in charge of the editable portion of the combo box.        /// 
        protected TextBox EditableTextBox        {            get            {                return base.GetTemplateChild("PART_EditableTextBox") as TextBox;            }        }           private string SelectedText        {            get            {                try                {                    if (this.SelectedIndex == -1) return null;                                      if (this.SelectedItem != null)                    {                        return this.SelectedItem.GetType().GetProperty(this.DisplayMemberPath).GetValue(this.SelectedItem, null).ToString();                    }                    else                    {                        return null;                    }                }                catch (System.Exception)                {                    return null;                }            }        }        #endregion    }