WPF editable combobox slow typing - wpf

Question

I have a WPF combobox like this :
<ComboBox x:Name="CustomerComboBox" IsEditable="True" ItemsSource="{Binding Relations.View}"
DisplayMemberPath="Model.sname" />
If I click in the editable combo while the binding is in place (MVVM) to give it focus, and I then press and hold any key, I assume the combo will be filled with that key rather quickly, but it isn't.
If I remove the displaymemberpath and then do the same, then I have the expected behavior. Of course I really need the binding.
The performance penalty only shows when the combo has a lot of elements mine has 6000.
I cannot understand where this performance penalty is coming from. Is there any way to bypass this problem ?

Answer 1

Below code solves the issues by creating a specialised combobox that basically caches all binding results. I created it by looking at the orginal source code of the combobox and itemscontrol using .NET reflector.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Reflection;
using System.ComponentModel;
using System.Collections.ObjectModel;
using System.Windows.Controls.Primitives;
using System.Collections;
namespace ICeTechControlLibrary
{
public class FastEditComboBox : ComboBox
{
//PARTS
private TextBox _TextBoxPart = null;
//DEPENDENCY PROPERTIES
public static readonly DependencyProperty TextProperty
= DependencyProperty.Register("Text", typeof(string), typeof(AutoCompleteTextBox), new FrameworkPropertyMetadata(string.Empty, FrameworkPropertyMetadataOptions.Journal | FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, new PropertyChangedCallback(FastEditComboBox.OnTextChanged)));
private List<string> _CompletionStrings = new List<string>();
private int _textBoxSelectionStart;
private bool _updatingText;
private bool _updatingSelectedItem;
private static Dictionary<TextBox, FastEditComboBox> _TextBoxDictionary = new Dictionary<TextBox,FastEditComboBox>();
static FastEditComboBox()
{
EventManager.RegisterClassHandler(typeof(TextBox), TextBox.TextChangedEvent, new TextChangedEventHandler(FastEditComboBox.OnTextChanged));
EventManager.RegisterClassHandler(typeof(TextBox), TextBox.SelectionChangedEvent, new RoutedEventHandler(FastEditComboBox.OnSelectionChanged));
}
public string Text
{
get
{
return (string)base.GetValue(TextProperty);
}
set
{
base.SetValue(TextProperty, value);
}
}
public override void OnApplyTemplate()
{
base.OnApplyTemplate();
_TextBoxPart = base.GetTemplateChild("PART_EditableTextBox") as TextBox;
if (!_TextBoxDictionary.ContainsKey(_TextBoxPart)) _TextBoxDictionary.Add(_TextBoxPart, this);
}
private void OnTextBoxSelectionChanged(object sender, RoutedEventArgs e)
{
this._textBoxSelectionStart = this._TextBoxPart.SelectionStart;
}
private void OnTextBoxTextChanged(object sender, TextChangedEventArgs e)
{
if (IsEditable)
{
TextUpdated(_TextBoxPart.Text, true);
}
}
private void TextUpdated(string newText, bool textBoxUpdated)
{
if (!_updatingText && !_updatingSelectedItem)
{
try
{
_updatingText = true;
if (base.IsTextSearchEnabled)
{
int num = FindMatchingPrefix(newText);
if (num >= 0)
{
if (textBoxUpdated)
{
int selectionStart = this._TextBoxPart.SelectionStart;
if ((selectionStart == newText.Length) && (selectionStart > this._textBoxSelectionStart))
{
string primaryTextFromItem = _CompletionStrings[num];
this._TextBoxPart.Text = primaryTextFromItem;
this._TextBoxPart.SelectionStart = newText.Length;
this._TextBoxPart.SelectionLength = primaryTextFromItem.Length - newText.Length;
newText = primaryTextFromItem;
}
}
else
{
string b = _CompletionStrings[num];
if (!string.Equals(newText, b, StringComparison.CurrentCulture))
{
num = -1;
}
}
}
if (num != base.SelectedIndex)
{
SelectedIndex = num;
}
}
if (textBoxUpdated)
{
Text = newText;
}
else if (_TextBoxPart != null)
{
_TextBoxPart.Text = newText;
}
}
finally
{
_updatingText = false;
}
}
}
internal void SelectedItemUpdated()
{
try
{
this._updatingSelectedItem = true;
if (!this._updatingText)
{
string primaryTextFromItem = GetPrimaryTextFromItem(SelectedItem);
Text = primaryTextFromItem;
}
this.Update();
}
finally
{
this._updatingSelectedItem = false;
}
}
private void Update()
{
if (this.IsEditable)
{
this.UpdateEditableTextBox();
}
else
{
//this.UpdateSelectionBoxItem();
}
}
private void UpdateEditableTextBox()
{
if (!_updatingText)
{
try
{
this._updatingText = true;
string text = this.Text;
if ((this._TextBoxPart != null) && (this._TextBoxPart.Text != text))
{
this._TextBoxPart.Text = text;
this._TextBoxPart.SelectAll();
}
}
finally
{
this._updatingText = false;
}
}
}
protected override void OnSelectionChanged(SelectionChangedEventArgs e)
{
base.RaiseEvent(e);
this.SelectedItemUpdated();
if (this.IsDropDownOpen)
{
object Item = SelectedItem;
if (Item != null)
{
base.OnSelectionChanged(e);
}
//object internalSelectedItem = base.InternalSelectedItem;
//if (internalSelectedItem != null)
//{
// base.NavigateToItem(internalSelectedItem, ItemsControl.ItemNavigateArgs.Empty);
//}
}
}
int FindMatchingPrefix(string s)
{
int index = _CompletionStrings.BinarySearch(s, StringComparer.OrdinalIgnoreCase);
if (index >= 0) return index;
index = ~index;
string p = _CompletionStrings[index];
if (p.StartsWith(s, StringComparison.CurrentCultureIgnoreCase)) return index;
return -1;
}
protected override void OnDisplayMemberPathChanged(string oldDisplayMemberPath, string newDisplayMemberPath)
{
FillCompletionStrings();
}
protected override void OnItemsChanged(System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
{
base.OnItemsChanged(e);
switch (e.Action)
{
case System.Collections.Specialized.NotifyCollectionChangedAction.Add:
AddCompletionStrings(e.NewItems);
break;
case System.Collections.Specialized.NotifyCollectionChangedAction.Remove:
RemoveCompletionStrings(e.OldItems);
break;
case System.Collections.Specialized.NotifyCollectionChangedAction.Reset:
FillCompletionStrings();
break;
}
}
private void FillCompletionStrings()
{
_CompletionStrings.Clear();
AddCompletionStrings(Items);
}
private void RemoveCompletionStrings(IList items)
{
foreach (object o in items)
{
RemoveCompletionStringForItem(o);
}
}
private void AddCompletionStrings(IList items)
{
foreach (object o in items)
{
AddCompletionStringForItem(o);
}
}
private void AddCompletionStringForItem(object item)
{
Binding binding = new Binding(DisplayMemberPath);
TextBlock tb = new TextBlock();
tb.DataContext = item;
tb.SetBinding(TextBlock.TextProperty, binding);
string s = tb.Text;
int index = _CompletionStrings.BinarySearch(s, StringComparer.OrdinalIgnoreCase);
if (index < 0)
{
_CompletionStrings.Insert(~index, s);
}
else
{
_CompletionStrings.Insert(index, s);
}
}
private string GetPrimaryTextFromItem(object item)
{
Binding binding = new Binding(DisplayMemberPath);
TextBlock tb = new TextBlock();
tb.DataContext = item;
tb.SetBinding(TextBlock.TextProperty, binding);
string s = tb.Text;
return s;
}
private void RemoveCompletionStringForItem(object item)
{
Binding binding = new Binding(DisplayMemberPath);
TextBlock tb = new TextBlock();
tb.DataContext = item;
tb.SetBinding(TextBlock.TextProperty, binding);
string s = tb.Text;
int index = _CompletionStrings.BinarySearch(s, StringComparer.OrdinalIgnoreCase);
if (index >= 0) _CompletionStrings.RemoveAt(index);
}
private static void OnTextChanged(object sender, TextChangedEventArgs e)
{
TextBox tb = e.Source as TextBox;
if (tb.Name == "PART_EditableTextBox")
{
if (_TextBoxDictionary.ContainsKey(tb))
{
FastEditComboBox combo = _TextBoxDictionary[tb];
combo.OnTextBoxTextChanged(sender, e);
e.Handled = true;
}
}
}
private static void OnSelectionChanged(object sender, RoutedEventArgs e)
{
TextBox tb = e.Source as TextBox;
if (tb.Name == "PART_EditableTextBox")
{
if (_TextBoxDictionary.ContainsKey(tb))
{
FastEditComboBox combo = _TextBoxDictionary[tb];
combo.OnTextBoxSelectionChanged(sender, e);
e.Handled = true;
}
}
}
private static void OnTextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
FastEditComboBox actb = (FastEditComboBox)d;
actb.TextUpdated((string)e.NewValue, false);
}
}
}
selecting the very first element clears the selection with this implementation.
so still some bugs here