demo_hard/SallerWindow.axaml

<Window xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
        x:Class="demo_hard.SallerWindow"
        x:CompileBindings="False"
        Title="SallerWindow">
    <DockPanel>
        <StackPanel Orientation="Horizontal" HorizontalAlignment="Center" DockPanel.Dock="Top" Margin="5">
            <TextBlock Text="Добро пожаловать в окно создания заказа"/>
        </StackPanel>
        <StackPanel DockPanel.Dock="Left" Orientation="Vertical" VerticalAlignment="Center" Margin="5">
            <TextBox x:Name="SearchBox" Width="200" TextChanged="SearchBox_Changed"/>
            <ListBox x:Name="SearchResultsListBox">
                <ListBox.ItemTemplate>
                    <DataTemplate>
                        <TextBlock Text="{Binding}"/> 
                    </DataTemplate>
                </ListBox.ItemTemplate>
            </ListBox>
        </StackPanel>
        <StackPanel VerticalAlignment="Center" Orientation="Vertical" Margin="5">
            <TextBlock Text="Номер заказа" Margin="5" HorizontalAlignment="Center"/>
            <AutoCompleteBox x:Name="CompleteBox" FilterMode="StartsWith" Width="200" HorizontalAlignment="Center" Margin="5"/>
            <TextBlock Text="Сделать штрих кода надо" Margin="5" HorizontalAlignment="Center"/>
            
            <ComboBox x:Name="Clients_ComboBox" Width="200" SelectionChanged="Clients_ComboBox_SelectionChanged" HorizontalAlignment="Center" Margin="5">
                <ComboBox.ItemTemplate>
                    <DataTemplate>
                        <TextBlock Text="{Binding Fio}"/>
                    </DataTemplate>
                </ComboBox.ItemTemplate>
            </ComboBox>
            
            <ComboBox x:Name="Service_Combobox" Width="200" SelectionChanged="Service_Combobox_SelectionChanged" HorizontalAlignment="Center" Margin="5">
                <ComboBox.ItemTemplate>
                    <DataTemplate>
                        <TextBlock Text="{Binding ServiceName}"/>
                    </DataTemplate>
                </ComboBox.ItemTemplate>
            </ComboBox>
            
            <Button Content="Добавить услугу" Click="AddService_Button" HorizontalAlignment="Center" Margin="5"/>
            
            <ListBox x:Name="SelectedServicesListBox" Width="200" Height="100" HorizontalAlignment="Center" Margin="5">
                <ListBox.ItemTemplate>
                    <DataTemplate>
                        <TextBlock Text="{Binding}"/>
                    </DataTemplate>
                </ListBox.ItemTemplate>
            </ListBox>

            <Button Content="Назад" Click="Go_Back_Button" HorizontalAlignment="Center" Margin="5"/>
            <Button Content="Создать штрих код" HorizontalAlignment="Center" Margin="5"/>
            <Button Content="Добавить Пользователя" Click="AddUser_Button" HorizontalAlignment="Center" Margin="5"/>
        </StackPanel>
    </DockPanel>
</Window>