MainWindow.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"
        xmlns:avaloniaBugs="clr-namespace:AvaloniaBugs"
        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
        x:Class="AvaloniaBugs.MainWindow"
        x:DataType="avaloniaBugs:MainWindowViewModel"
        x:Name="Root"
        Title="AvaloniaBugs">
  <Window.DataContext>
    <avaloniaBugs:MainWindowViewModel />
  </Window.DataContext>
  <DockPanel>
    <Menu DockPanel.Dock="Top">
      <MenuItem Header="New tab" Command="{CompiledBinding NewTab}" />
      <MenuItem Header="Close all tabs" Command="{CompiledBinding CloseAllTabs}" />
    </Menu>
    <TabStrip DockPanel.Dock="Top" SelectedItem="{CompiledBinding SelectedFile, Mode=TwoWay}" ItemsSource="{CompiledBinding Files}" x:Name="TabStrip">
      <TabStrip.Styles>
        <Style Selector="TabStripItem">
          <Setter Property="Template">
            <ControlTemplate>
              <DockPanel>
                <Button  x:DataType="avaloniaBugs:BigFileViewModel" DockPanel.Dock="Right" Command="{CompiledBinding #Root.((avaloniaBugs:MainWindowViewModel)DataContext).CloseTab}" CommandParameter="{CompiledBinding .}" Content="x" />
                <TextBlock x:DataType="avaloniaBugs:BigFileViewModel" Text="{CompiledBinding Title}" />
              </DockPanel>
            </ControlTemplate>
          </Setter>
        </Style>
      </TabStrip.Styles>
    </TabStrip>
    <ContentControl Content="{CompiledBinding #TabStrip.SelectedItem}">
      <ContentControl.ContentTemplate>
        <DataTemplate>
          <avaloniaBugs:FileView />
        </DataTemplate>
      </ContentControl.ContentTemplate>
    </ContentControl>
  </DockPanel>
</Window>