ComboBox default text show typeName of items type, instead of my own text property

I have template for my ComboBox. taken from here. Lets say each item is Node type.

Its all work perfect, but one thing crash my mind. When I click between ComboBoxItem (this area i think one-pixel line), Text of ComboBox changed to TypeName of items (with namespace).

I have overrided ToString() method of Node class, but CallStack shows, that program comes to it from [External code].

What should I do to ComboBox.Text show my string property instead of TypeName of ComboBoxItem?

If I miss some detail, just point out what is.

Edit:

Code is from hyperlink here above, with some changes.

Usage:

<vm:ComboCheckBox Grid.Column="1" ItemsSource="{Binding Path=Months}"
                  DefaultText="Select months"/>

Months is ObservableNodeCollection.

Template[I don't place here resources. they are the same, as at link]:

<ComboBox   ItemsSource="{Binding ElementName=UserControl, Path=ItemsSource}"
            DataContext="{Binding ElementName=UserControl, Path=DataContext}"
            Text="{Binding Path=Text, Mode=OneWay, ElementName=UserControl, UpdateSourceTrigger=PropertyChanged}"
            Focusable="False"
            IsEditable="False"
            Loaded="CheckableCombo_Loaded"

            x:Name="CheckableCombo"
            SnapsToDevicePixels="True"
            OverridesDefaultStyle="True"
            ScrollViewer.HorizontalScrollBarVisibility="Auto"
            ScrollViewer.VerticalScrollBarVisibility="Auto"
            ScrollViewer.CanContentScroll="True"
            IsSynchronizedWithCurrentItem="True"
            MinWidth="120"
            MinHeight="20"
            >
    <ComboBox.ItemTemplate>
        <HierarchicalDataTemplate>
                <CheckBox Margin="0" IsChecked="{Binding Path=IsSelected}"
                          Command="{Binding Path=CheckBoxStateChanged, ElementName=UserControl}" CommandParameter="{Binding}"
                          Content="{Binding Path=Title}" />
        </HierarchicalDataTemplate>
    </ComboBox.ItemTemplate>
    <ComboBox.Template>
        <ControlTemplate TargetType="ComboBox">
            <Grid>
                <ToggleButton 
                                    Name="ToggleButton" 
                                    Template="{StaticResource ComboBoxToggleButton}" 
                                    Grid.Column="2" 
                                    Focusable="false"
                                    IsChecked="{Binding Path=IsDropDownOpen,Mode=TwoWay,RelativeSource={RelativeSource TemplatedParent}}"
                                    ClickMode="Press">
                </ToggleButton>
                <ContentPresenter
                                    x:Name="Presenter"
                                    IsHitTestVisible="False" 
                                    Margin="3,3,23,3"
                                    VerticalAlignment="Center"
                                    HorizontalAlignment="Left">
                    <ContentPresenter.Content>
                        <TextBlock TextTrimming="CharacterEllipsis"
                                            Text="{Binding Path=Text,Mode=OneWay,RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=ComboBox}}" />
                    </ContentPresenter.Content>
                </ContentPresenter>
                <TextBox x:Name="EditableTextBox"
                         Style="{x:Null}" 
                         Template="{StaticResource ComboBoxTextBox}" 
                         HorizontalAlignment="Left" 
                         VerticalAlignment="Center" 
                         Margin="3,3,23,3"
                         Focusable="True"
                         Background="Transparent"
                         Visibility="Hidden"
                         IsReadOnly="{TemplateBinding IsReadOnly}"/>
                <Popup Name="Popup"
                       Placement="Bottom"
                       IsOpen="{TemplateBinding IsDropDownOpen}"
                       AllowsTransparency="True" 
                       Focusable="False"
                       PopupAnimation="Slide">
                    <Grid Name="DropDown"
                          ShowGridLines="True"
                          SnapsToDevicePixels="True"                
                          MinWidth="{TemplateBinding ActualWidth}"
                          MaxHeight="{TemplateBinding MaxDropDownHeight}">
                        <Border Focusable="False"
                                x:Name="DropDownBorder"
                                Background="{StaticResource WindowBackgroundBrush}"
                                BorderThickness="1"
                                BorderBrush="{StaticResource SolidBorderBrush}"/>
                        <ScrollViewer Margin="4,6,4,6" SnapsToDevicePixels="True" DataContext="{Binding}">
                            <StackPanel IsItemsHost="True" KeyboardNavigation.DirectionalNavigation="Cycle" KeyboardNavigation.ControlTabNavigation="Cycle" />
                        </ScrollViewer>
                    </Grid>
                </Popup>
            </Grid>
            <ControlTemplate.Triggers>
                <Trigger Property="HasItems" Value="false">
                    <Setter TargetName="DropDownBorder" Property="MinHeight" Value="95"/>
                </Trigger>
                <Trigger Property="IsEnabled" Value="false">
                    <Setter Property="Foreground" Value="{StaticResource DisabledForegroundBrush}"/>
                </Trigger>
                <Trigger Property="IsGrouping" Value="true">
                    <Setter Property="ScrollViewer.CanContentScroll" Value="false"/>
                </Trigger>
                <Trigger SourceName="Popup" Property="Popup.AllowsTransparency" Value="true">
                    <Setter TargetName="DropDownBorder" Property="CornerRadius" Value="4"/>
                    <Setter TargetName="DropDownBorder" Property="Margin" Value="0,2,0,0"/>
                </Trigger>
                <Trigger Property="IsEditable" Value="true">
                    <Setter Property="IsTabStop" Value="false"/>
                    <Setter TargetName="EditableTextBox" Property="V开发者_如何学编程isibility" Value="Visible"/>
                    <Setter TargetName="Presenter" Property="Visibility" Value="Hidden"/>
                </Trigger>
            </ControlTemplate.Triggers>
        </ControlTemplate>
    </ComboBox.Template>
</ComboBox>

CodeBehind:

/// <summary>
/// Interaction logic for ComboCheckBox.xaml
/// </summary>
public partial class ComboCheckBox : UserControl
{
    public ObservableNodeCollection ItemsSource 
    {
        get 
        { 
            return (ObservableNodeCollection)GetValue(ItemsSourceProperty); 
        } 
        set 
        {
            SetValue(ItemsSourceProperty, value);
            SetText();
        }
    }

    public static readonly DependencyProperty ItemsSourceProperty =
        DependencyProperty.Register("ItemsSource", typeof(ObservableNodeCollection), typeof(ComboCheckBox), new UIPropertyMetadata(null)); 

    /// <summary> 
    /// Gets or sets the text displayed in the ComboBox 
    /// </summary> 
    public string Text 
    { 
        get
        { 
            return(string)GetValue(TextProperty); 
        }
        set 
        { 
            SetValue(TextProperty, value);
        } 
    } 

    public static readonly DependencyProperty TextProperty = 
        DependencyProperty.Register("Text", typeof(string), typeof(ComboCheckBox), new UIPropertyMetadata(string.Empty)); 


    /// <summary> 
    /// Gets or sets the text displayed in the ComboBox if there are no selected items 
    /// </summary> 
    public string DefaultText 
    { 
        get
        {
            return(string)GetValue(DefaultTextProperty);
        }
        set
        {
            SetValue(DefaultTextProperty, value);
            SetText();
        }
    }

    public static readonly DependencyProperty DefaultTextProperty = 
        DependencyProperty.Register("DefaultText", typeof(string), typeof(ComboCheckBox), new UIPropertyMetadata(string.Empty)); 

    public ComboCheckBox()
    {
        InitializeComponent();
        this.SetText();
    }

    public ICommand CheckBoxStateChanged
    {
        get
        {
            return new Helpers.DelegateCommand<Node>((Node parameter) =>
            {
                if (parameter.IsSelectAllNode)
                {
                    bool? isSelected = this.ItemsSource[0].IsSelected;
                    ItemsSource.ToList().ForEach(item => item.IsSelected = isSelected);
                }
                else
                {
                    if (this.ItemsSource[0].IsSelectAllNode)
                    {
                        bool isAllTrue = true, isAllFalse = true;
                        for (int i = 1; i < this.ItemsSource.Count; i++)
                        {
                            isAllTrue = isAllTrue && this.ItemsSource[i].IsSelected.Value;
                            isAllFalse = isAllFalse && !this.ItemsSource[i].IsSelected.Value;
                        }
                        if (isAllTrue)
                            this.ItemsSource[0].IsSelected = true;
                        else if (isAllFalse)
                            this.ItemsSource[0].IsSelected = false;
                        else
                            this.ItemsSource[0].IsSelected = null;
                    }
                }
                this.SetText();
            });
        }
    }

    private void SetText()
    {
        string answer = String.Empty;
        if (ItemsSource != null)
            answer = ItemsSource.ToString();
        if (String.IsNullOrWhiteSpace(answer))
            answer = this.DefaultText;
        this.Text = answer;
    }

    private void CheckableCombo_Loaded(object sender, RoutedEventArgs e)
    {
        this.SetText();
    }
}

Node class:

public class Node : ObservableObject
{
    public Node(string title, string header = "",  bool isSelectAllNode = false, bool? isSelected = false)
    {
        this.Title = title;
        if (String.IsNullOrEmpty(header))
            this.Header = title;
        else
            this.Header = header;
        this.IsSelectAllNode = isSelectAllNode;
        this.IsSelected = isSelected;
    }
    public string Header { get; set; }
    public string Title { get; set; }
    private bool? isSelected;
    private const string IsSelectedPropertyName = "IsSelected";
    public bool? IsSelected
    {
        get
        {
            return this.isSelected;
        }
        set
        {
            this.isSelected = value;
            this.OnPropertyChanged(IsSelectedPropertyName);
        }
    }
    public bool IsSelectAllNode { get; set; }
    public override string ToString()
    {
        return "123";//if miss it, the typeName will return.
    }
}

ObservableNodeCollection:

public class ObservableNodeCollection : ObservableCollection<Node>
{
    public ObservableNodeCollection()
    {
    }
    public ObservableNodeCollection(List<Node> list)
        : base(list)
    {
    }
    public ObservableNodeCollection(IEnumerable<Node> collection)
        : base(collection)
    {
    }

    public override string ToString()
    {
        string answer = String.Empty;
        if (this.Items != null)
        {
            StringBuilder outString = new StringBuilder();
            foreach (Node node in this.Items)
                if (node.IsSelected == true && !node.IsSelectAllNode)
                {
                    outString.Append(node.Header);
                    outString.Append(", ");
                }
            answer = outString.ToString().TrimEnd(new char[] { ',', ' ' });
        }
        return answer;
    }
}

EDIT 2:

Inside of the ViewModel constructor of the main window exist this code

        int i;
        //Initialize months for combobox
        this.Months = new ObservableNodeCollection(new List<Node>() { new Node("SelectAll", isSelectAllNode:true)});

        for (i=0; i < DateTimeFormatInfo.CurrentInfo.MonthNames.Length; i++)
        {
            if (!String.IsNullOrEmpty(DateTimeFormatInfo.CurrentInfo.MonthNames[i]))
                this.Months.Add(
                    new Node
                        (   
                            DateTimeFormatInfo.CurrentInfo.MonthNames[i], 
                            DateTimeFormatInfo.CurrentInfo.AbbreviatedMonthNames[i]
                        ));
        }

so, this.Months - is a ObservableNodeCollection, which have 1-st element is SelectAll, and other 12 elements is a months.

So you're saying that if you remove the Node.ToString() method it displays the TypeName of the Node?

That is the expected behavior. Your ComboBox items are bound to each item in your ObservableCollection, and when binding an object to a Text property, the ToString method is always used.

You can set the ComboBox.Text property manually, however it is changed to SelectedItem.ToString() whenever the selected ComboBox item changes. By default this resolves to the TypeName of the ComboBox's data item, however you can change this by overriding the ToString() method of the data item, or by setting the ComboBox.DisplayMemberPath to a property that exists on the data item

<ComboBox ItemsSource="{Binding Months}"
          DisplayMemberPath="Header" />

Try the DisplayMemberPath property of your ComboBox