PleasantUI

Repositories: Original (Onebeld) · Fork (ghudulf)

PleasantUI is a cross-platform UI theme and control library for Avalonia, inspired by Microsoft Fluent Design and the WinUI/UWP visual language. It completely re-styles every standard Avalonia control and adds a suite of custom controls, a multi-theme engine with custom theme support, a reactive localization system, and a custom window chrome — all AOT-compatible with no rd.xml required.

The project has been in active development since 2021, originally as part of the Regul and Regul Save Cleaner projects.

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Features

Complete Fluent-style control theming

Every standard Avalonia control gets a full Fluent Design makeover — rounded corners, layered fill colors, smooth pointer-over and pressed transitions, and accent color integration:

Control	Control	Control
Button (+ AppBar, Accent, Danger variants)	CheckBox	RadioButton
ToggleButton / ToggleSwitch	RepeatButton / ButtonSpinner	Slider
TextBox / AutoCompleteBox	NumericUpDown	ComboBox / DropDownButton
Calendar / CalendarDatePicker / TimePicker	DataGrid	ListBox / TreeView
Expander	TabControl / TabItem	ScrollBar / ScrollViewer
ProgressBar	Menu / ContextMenu	ToolTip
Carousel	Separator	NotificationCard

Custom Pleasant controls

Controls built from scratch that go beyond what Avalonia ships:

Control	Description
PleasantWindow	Custom window chrome with a Fluent title bar, subtitle, custom icon/title content, optional blur, content-extends-into-titlebar, and macOS caption override
NavigationView / NavigationViewItem	Collapsible side navigation panel, similar to WinUI NavigationView
PleasantTabView / PleasantTabItem	Chromium-style tab strip with add/close buttons and scrollable tab bar
ContentDialog	Modal overlay dialog with bottom button panel and smooth scroll content area
PleasantSnackbar	Temporary non-intrusive notification bar
ProgressRing	Circular progress indicator — both determinate and indeterminate with animated arc
OptionsDisplayItem	Settings-style row with header, description, icon, action button slot, navigation chevron, and expandable content
InformationBlock	Compact pill-shaped label combining an icon and a value
MarkedTextBox / MarkedNumericUpDown	Input controls with inline label/unit markers
RippleEffect	Material-style ripple click feedback
SmoothScrollViewer	ScrollViewer with inertia gesture support
PleasantMiniWindow	Lightweight floating window

Theme engine

• Built-in themes: Light, Dark, Mint, Strawberry, Ice, Sunny, Spruce, Cherry, Cave, Lunar
• System mode — follows the OS light/dark preference automatically
• Custom themes — create, edit, export, import, and persist your own color palettes via the built-in ThemeEditorWindow
• Accent color follows the OS accent or can be overridden per-user; light/dark variants and gradient pairs are generated automatically
• Settings are persisted to disk automatically on desktop; mobile apps can save manually

Localization system

• Localizer singleton backed by .NET ResourceManager — add any number of .resx resource files
• {Localize Key} AXAML markup extension binds reactively — switching language updates every bound string instantly without reloading views
• Localizer.TrDefault(key, fallback) for safe lookups that fall back to a raw string instead of an error message
• LocalizationChanged event for view models and code-behind to react to language switches

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Packages

Package	Description
PleasantUI	Core theme, all control styles, Pleasant controls, theme engine, localization
PleasantUI.ToolKit	MessageBox, ThemeEditorWindow, color picker utilities
PleasantUI.MaterialIcons	Material Design icon geometry library for use with PathIcon
PleasantUI.DataGrid	Fluent-styled DataGrid extension

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Documentation

Detailed reference docs for each control are in the docs/ folder:

Doc	Controls
PleasantWindow	PleasantWindow, IPleasantSplashScreen
PleasantMiniWindow	PleasantMiniWindow
NavigationView	NavigationView, NavigationViewItem
PleasantTabView	PleasantTabView, PleasantTabItem
ContentDialog	ContentDialog
MessageBox	MessageBox (ToolKit)
PleasantDialog	PleasantDialog (ToolKit)
PleasantSnackbar	PleasantSnackbar
ProgressRing	ProgressRing
OptionsDisplayItem	OptionsDisplayItem
InformationBlock	InformationBlock
DataGrid	PleasantUI.DataGrid package
Localization	Localizer, {Localize} markup extension
Theme Engine	PleasantTheme, custom themes, color tokens

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Getting Started

Install

Package List (Avalonia 12)

Published on NuGet:

<PackageReference Include="PleasantUI" Version="5.1.0-alpha4.2" />
<PackageReference Include="PleasantUI.DataGrid" Version="5.1.0-alpha4.2" />
<PackageReference Include="PleasantUI.MaterialIcons" Version="5.1.0-alpha4.2" />
<PackageReference Include="PleasantUI.ToolKit" Version="5.1.0-alpha4.2" />

Add the theme

In your App.axaml, add PleasantTheme to your styles:

<Application xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             x:Class="YourApp.App">
    <Application.Styles>
        <PleasantTheme />
    </Application.Styles>
</Application>

Initialize correctly

Make sure AvaloniaXamlLoader.Load(this) is called in Initialize():

public partial class App : Application
{
    public override void Initialize()
    {
        AvaloniaXamlLoader.Load(this); // required
    }

    public override void OnFrameworkInitializationCompleted()
    {
        if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
        {
            desktop.MainWindow = new MainWindow
            {
                DataContext = new MainWindowViewModel(),
            };
        }

        base.OnFrameworkInitializationCompleted();
    }
}

Use PleasantWindow

Replace Window with PleasantWindow to get the custom Fluent title bar:

using PleasantUI.Controls;

public partial class MainWindow : PleasantWindow
{
    public MainWindow() => InitializeComponent();
}

<PleasantWindow 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="YourApp.Views.MainWindow"
                Title="Avalonia Application">
</PleasantWindow>

Key PleasantWindow properties:

Property	Type	Description
TitleBarType	Classic / ClassicExtended	Title bar layout style
ExtendsContentIntoTitleBar	bool	Lets content render behind the title bar
Subtitle	string	Secondary text shown next to the title
DisplayIcon	object	Custom icon content in the title bar
DisplayTitle	object	Custom title content (e.g. a PathIcon)
EnableBlur	bool	Acrylic/blur window background
CaptionButtons	enum	Which caption buttons to show
LeftTitleBarContent	object	Content injected left of the title

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Localization

Register your .resx resource managers in your Application constructor:

public App()
{
    Localizer.AddRes(new ResourceManager(typeof(Properties.Localizations.App)));
    Localizer.ChangeLang("en");
}

Use {Localize Key} in AXAML — updates live when the language changes:

<TextBlock Text="{Localize WelcomeMessage}" />
<Button Content="{Localize SaveButton}" />

Switch language at runtime:

Localizer.ChangeLang("ru");

Safe lookup with fallback in code-behind:

string title = Localizer.TrDefault("DialogTitle", "Confirm");

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Button variants

<Button Content="Default" />
<Button Theme="{StaticResource AccentButtonTheme}" Content="Accent" />
<Button Theme="{StaticResource DangerButtonTheme}" Content="Danger" />
<Button Theme="{StaticResource AppBarButtonTheme}" Content="AppBar" />

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OptionsDisplayItem

<!-- Navigation row -->
<OptionsDisplayItem Header="Account"
                    Description="Manage your account"
                    Icon="{x:Static MaterialIcons.AccountOutline}"
                    Navigates="True" />

<!-- Row with action control -->
<OptionsDisplayItem Header="Dark mode"
                    Icon="{x:Static MaterialIcons.WeatherNight}">
    <OptionsDisplayItem.ActionButton>
        <ToggleSwitch />
    </OptionsDisplayItem.ActionButton>
</OptionsDisplayItem>

<!-- Expandable row -->
<OptionsDisplayItem Header="Advanced" Expands="True">
    <OptionsDisplayItem.Content>
        <StackPanel>
            <CheckBox Content="Enable feature X" />
        </StackPanel>
    </OptionsDisplayItem.Content>
</OptionsDisplayItem>

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Screenshots

Regul Save Cleaner

OlibKey

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Credits

• AvaloniaUI
• Some controls inspired by PieroCastillo's Aura.UI
• ProgressRing by ymg2006
• Built with JetBrains Rider