<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"
        Width="400" Height="250"
        x:Class="AvaloniaUI.CenterScreen"
        Title="CenterScreen">
    <StackPanel Margin="10" HorizontalAlignment="Center" VerticalAlignment="Center">
        <Button Name="cmdCenter"
                Content="Center"
                Click="cmdCenter_Click"/>
    </StackPanel>
</Window>

using Avalonia;
using Avalonia.Controls;
using Avalonia.Interactivity;
using Avalonia.Markup.Xaml;

namespace AvaloniaUI;

public partial class CenterScreen : Window
{
    public CenterScreen()
    {
        InitializeComponent();
    }
    private void cmdCenter_Click(object? sender, RoutedEventArgs e)
    {
        var screen = Screens.ScreenFromWindow(this) ?? Screens.Primary;
        if (screen is null)
            return;

        // 工作区（排除任务栏等）
        var workArea = screen.WorkingArea;

        // 当前窗口大小（像素）
        var windowWidth = (int)Bounds.Width;
        var windowHeight = (int)Bounds.Height;

        var x = workArea.X + (workArea.Width - windowWidth) / 2;
        var y = workArea.Y + (workArea.Height - windowHeight) / 2;

        Position = new PixelPoint(x, y);
    }
}