test/FirstSlice/UserWindow.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" Height="300" Width="300"
        x:Class="FirstSlice.UserWindow"
        WindowStartupLocation="CenterOwner"
        Title="UserWindow">
        
        <Grid>
                <Grid.RowDefinitions>
                        <RowDefinition></RowDefinition>
                        <RowDefinition></RowDefinition>
                        <RowDefinition></RowDefinition>
                        <RowDefinition></RowDefinition>
                        <RowDefinition></RowDefinition>
                        <RowDefinition></RowDefinition>
                </Grid.RowDefinitions>
                
                <TextBox Grid.Row="0" Name="TextFullName" Watermark="ФИО" VerticalAlignment="Center" Margin="10"/>
                <TextBox Grid.Row="1" Name="TextBirthday" MaxLength="10" Watermark="Дата рождения" VerticalAlignment="Center" Margin="10"/>
                <TextBox Grid.Row="2" Name="TextPhoneNumber" MaxLength="11" Watermark="Номер телефона" VerticalAlignment="Center" Margin="10"/>
                <TextBox Grid.Row="3" Name="TextAddress" Watermark="Адрес" VerticalAlignment="Center" Margin="10"/>

                <ComboBox Grid.Row="4" Name="ComboRole" PlaceholderText="Роль" VerticalAlignment="Center" Margin="10">
                        <ComboBox.ItemTemplate>
                                <DataTemplate>
                                        <TextBlock Text="{Binding Name}"></TextBlock>
                                </DataTemplate>
                        </ComboBox.ItemTemplate>
                </ComboBox>
                
                <Button Grid.Row="5" Name="SaveUser" Content="Сохранить пользователя" Click="OnSaveUserClick" VerticalAlignment="Center" HorizontalAlignment="Left" Margin="10"></Button>
        </Grid>
        
</Window>