WPF find textbox control inside combo box with combobox.Template

Question

This question is extension to WPF ComboBox with checkboxes and textbox with search field

Adding the UserControl in my window as follows

<Usercontrols:MultiSelectComboBox x:Name="multiCombo" HorizontalAlignment="Left" Height="28" VerticalAlignment="Top" Width="235" Margin="81,27,0,0"/>

I am having my combobox.Template as follows in my combobox

<ComboBox>
<ComboBox.Template>
        <ControlTemplate TargetType="ComboBox">
            <Grid Name="control" >

                <ToggleButton 
                    x:Name="ToggleButton" 
                   Grid.Column="2" IsChecked="{Binding Path=IsDropDownOpen,Mode=TwoWay,RelativeSource={RelativeSource TemplatedParent}}"
                    Focusable="false"                           
                    ClickMode="Press" HorizontalContentAlignment="Left" >
                    <ToggleButton.Template>
                        <ControlTemplate>
                            <Grid>
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="*"/>
                                    <ColumnDefinition Width="18"/>
                                </Grid.ColumnDefinitions>
                                <Border
              x:Name="Border" 
              Grid.ColumnSpan="2"
              CornerRadius="2"
              Background="White"
              BorderBrush="Silver"
              BorderThickness="1,1,1,1" />
                                <Border 
                x:Name="BorderComp" 
              Grid.Column="0"
              CornerRadius="2" 
              Margin="1" 
             Background="White"
              BorderBrush="Black"
              BorderThickness="0,0,0,0" >
                                    <TextBlock Text="{Binding Path=Text,RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=UserControl}}" 
                                           Background="White" Padding="3" />
                                </Border>
                                <Path 
              x:Name="Arrow"
              Grid.Column="1"     
              Fill="Black"
              HorizontalAlignment="Center"
              VerticalAlignment="Center"
              Data="M 0 0 L 4 4 L 8 0 Z"/>
                            </Grid>
                        </ControlTemplate>
                    </ToggleButton.Template>
                </ToggleButton>
                <Popup 
Name="Popup"
Placement="Bottom"                        
AllowsTransparency="True" 
Focusable="False"  IsOpen="{TemplateBinding IsDropDownOpen}"
PopupAnimation="Slide">
                    <Grid 
    Name="DropDown"
    SnapsToDevicePixels="True"  
    MinWidth="{TemplateBinding ActualWidth}"
    MaxHeight="{TemplateBinding MaxDropDownHeight}">
                        <Border 
        x:Name="DropDownBorder"
        BorderThickness="1" Background="White"
        BorderBrush="Black"/>
                        <ScrollViewer Margin="4,6,4,6" SnapsToDevicePixels="True" DataContext="{Binding}">
                            <Grid>
                                <Grid.RowDefinitions>
                                    <RowDefinition Height="Auto" />
                                    <RowDefinition Height="*" />
                                </Grid.RowDefinitions>
                                <TextBox Name="TextBox"  Text="{Binding Path=Text, Mode=TwoWay}" TextChanged="TextBox_TextChanged" />
                                <StackPanel Grid.Row="2" IsItemsHost="True" KeyboardNavigation.DirectionalNavigation="Contained" />
                            </Grid>
                        </ScrollViewer>
                    </Grid>
                </Popup>
            </Grid>
            <ControlTemplate.Triggers>
                <Trigger Property="HasItems" Value="false">
                    <Setter TargetName="DropDownBorder" Property="MinHeight" Value="95"/>
                </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>
            </ControlTemplate.Triggers>
        </ControlTemplate>
    </ComboBox.Template>
</ComboBox>

I am trying to find the TextBox control inside UserControl with ComboBox and ComboBox.ItemTemplate on my text box changed event. I tried as below but i am getting null

private void multiCombo_TextChange(object sender, EventArgs e)
    {
        Grid TxtBox = (Grid)multiCombo.Template.FindName("control", multiCombo);
        //TextBox textBox = sender as TextBox;
        MessageBox.Show(TxtBox.ToString());
    }

Answer 1

You could cast the OriginalSource property of the TextChangedEventArgs :

private void multiCombo_TextChange(object sender, TextChangedEventArgs e)
{
    TextBox textBox = e.OriginalSource as TextBox;
    //...
}