Avalonia 11中动态变更主题和颜色的方法

      首先添加一个这个工具类：

using Avalonia.Controls.ApplicationLifetimes;
using Avalonia.Styling;
using Avalonia.Themes.Fluent;
using Avalonia.Themes.Simple;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace AvaloniaChangeTheme.Views
{
    public enum ThemeType
    {
        Fluent,
        Simple
    }

    public static class AppThemeUtils
    {
        private static readonly Styles _themeStylesContainer = new();
        private static FluentTheme _fluentTheme;
        private static SimpleTheme _simpleTheme;
        private static IStyle _colorPickerFluent, _colorPickerSimple;
        private static IStyle _dataGridFluent, _dataGridSimple;

        public static void BeforeInitialize()
        {
            App.Current.Styles.Add(_themeStylesContainer);
        }

        public static void AfterInitialize()
        {
            _fluentTheme = (FluentTheme)App.Current.Resources["FluentTheme"]!;
            _simpleTheme = (SimpleTheme)App.Current.Resources["SimpleTheme"]!;
            _colorPickerFluent = (IStyle)App.Current.Resources["ColorPickerFluent"]!;
            _colorPickerSimple = (IStyle)App.Current.Resources["ColorPickerSimple"]!;
            _dataGridFluent = (IStyle)App.Current.Resources["DataGridFluent"]!;
            _dataGridSimple = (IStyle)App.Current.Resources["DataGridSimple"]!;

            SetTheme(ThemeType.Fluent);
        }

        private static ThemeType _prevTheme;
        public static ThemeType CurrentTheme => _prevTheme;

        public static void SetTheme(ThemeType theme)
        {
            var app = (App)App.Current!;

            var prevTheme = _prevTheme;
            _prevTheme = theme;
            var shouldReopenWindow = prevTheme != theme;

            if (_themeStylesContainer.Count == 0)
            {
                _themeStylesContainer.Add(new Style());
                _themeStylesContainer.Add(new Style());
                _themeStylesContainer.Add(new Style());
            }

            if (theme == ThemeType.Fluent)
            {
                _themeStylesContainer[0] = _fluentTheme!;
                _themeStylesContainer[1] = _colorPickerFluent!;
                _themeStylesContainer[2] = _dataGridFluent!;
            }
            else if (theme == ThemeType.Simple)
            {
                _themeStylesContainer[0] = _simpleTheme!;
                _themeStylesContainer[1] = _colorPickerSimple!;
                _themeStylesContainer[2] = _dataGridSimple!;
            }

            if (shouldReopenWindow)
            {
                if (app.ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktopLifetime)
                {
                    var oldWindow = desktopLifetime.MainWindow;
                    var newWindow = new MainWindow();
                    desktopLifetime.MainWindow = newWindow;
                    newWindow.Show();
                    oldWindow?.Close();
                }
                else if (app.ApplicationLifetime is ISingleViewApplicationLifetime singleViewLifetime)
                {
                    singleViewLifetime.MainView = new MainView();
                }
            }
        }
    }

}

     在App.xaml中，将原来的这一段删掉，因为会在代码中创建：

 <Application.Styles>
     <FluentTheme/>
 </Application.Styles>

     添加下面的内容：

<Application.Resources>
    <ResourceDictionary>
        <!-- Resources used only in the control catalog -->
        <ResourceDictionary.ThemeDictionaries>
            <ResourceDictionary x:Key="Default">
                <Color x:Key="CatalogBaseLowColor">#33000000</Color>
                <Color x:Key="CatalogBaseMediumColor">#99000000</Color>
                <Color x:Key="CatalogChromeMediumColor">#FFE6E6E6</Color>
                <Color x:Key="CatalogBaseHighColor">#FF000000</Color>
            </ResourceDictionary>
            <ResourceDictionary x:Key="Dark">
                <Color x:Key="CatalogBaseLowColor">#33FFFFFF</Color>
                <Color x:Key="CatalogBaseMediumColor">#99FFFFFF</Color>
                <Color x:Key="CatalogChromeMediumColor">#FF1F1F1F</Color>
                <Color x:Key="CatalogBaseHighColor">#FFFFFFFF</Color>
            </ResourceDictionary>
        </ResourceDictionary.ThemeDictionaries>

        <!-- Styles attached dynamically depending on current theme (simple or fluent) -->
        <FluentTheme x:Key="FluentTheme">
        </FluentTheme>
        <SimpleTheme x:Key="SimpleTheme" />
        <StyleInclude x:Key="DataGridFluent" Source="avares://Avalonia.Controls.DataGrid/Themes/Fluent.xaml" />
        <StyleInclude x:Key="DataGridSimple" Source="avares://Avalonia.Controls.DataGrid/Themes/Simple.xaml" />
        <StyleInclude x:Key="ColorPickerFluent" Source="avares://Avalonia.Controls.ColorPicker/Themes/Fluent/Fluent.xaml" />
        <StyleInclude x:Key="ColorPickerSimple" Source="avares://Avalonia.Controls.ColorPicker/Themes/Simple/Simple.xaml" />
    </ResourceDictionary>
</Application.Resources>

       完整示例可以看这里：

https://github.com/bodong1987/AvaloniaSamples/tree/main/AvaloniaChangeTheme