FlagstoneUI

FlagstoneUI

True cross‑platform UI for .NET MAUI — one control surface, consistent behaviour everywhere, no platform code.

FlagstoneUI removes the last barrier to building visually consistent .NET MAUI apps.

.NET MAUI gets you most of the way there, but as soon as you need a custom border, corner radius, or background on a text input, you fall through a gap, and end up in platform handlers for iOS, Android, and Windows.

FlagstoneUI closes those gaps. It gives you enhanced, neutral controls designed for full visual control from shared code. No renderers. No handlers. No platform quirks. Just the UI your app is meant to have, working the same on every device.

⚠️ Early experimental project. Functional and ready for testing, but evolving quickly.

What’s Available Now

• Core controls: FsButton, FsEntry, FsCard, FsEditor

• Token‑based theming system (colour, spacing, shapes, typography)

• Material theme (NuGet) + example themes in the sample app

• Community Toolkit integrations:

  • ValidationBehaviorAdapter for reuse of existing validators
  • Optional animated border behaviour for FsEditor

Themes are standard resource dictionaries — copy, customise, extend, or publish your own.

Why FlagstoneUI?

The gap in .NET MAUI

.NET MAUI’s default controls look native, and relatively consistent, but many visual properties simply aren't exposed.

<Entry Placeholder="Email" />

Looks simple. But here's an example of how an Entry is rendered on each platform:

Now imagine your designer specifies:

• CornerRadius: 8
• BorderWidth: 2
• BorderColor: #2196F3

To implement that in .NET MAUI, you'll need custom handler code for iOS, Android, and Windows, and you'll maintain that code forever — including variants:

• Write a handler to modify UITextField for iOS and macOS (and understand what that means)
• Write a separate handler to modify EditText for Android (and understand that platform's APIs)
• Write yet another handler to modify TextBox for Windows (and learn those platform-specific details)
• Create variants for different styles (primary, secondary, different input purposes) in each handler
• Create variants for different states (focused, disabled, valid, invalid, error) in each handler
• Maintain all three handlers, forever, as platforms evolve and APIs change

FlagstoneUI’s approach

FlagstoneUI gives you controls designed for full visual control from shared code.

<FsEntry
    Placeholder="Email"
    CornerRadius="8"
    BorderColor="#2196F3"
    BorderWidth="2" />

And you can use explicit styles for your variants and states, or Visual State Manager, all in .NET MAUI, without touching platform code.

One place. One API. Same behaviour everywhere.

This is the layer that makes .NET MAUI feel complete: define your visual system once, and your entire app uses it.

Quick Start

📚 Documentation | 🚀 Quickstart

Build from Source

# Clone and explore
git clone https://github.com/matt-goldman/flagstone-ui.git
cd flagstone-ui

dotnet build

# Run sample app
dotnet run --project samples/FlagstoneUI.SampleApp

Or reference FlagstoneUI.Core in your MAUI project.

Install via NuGet (Preview)

dotnet add package FlagstoneUI.Core --version 0.0.1-preview1

dotnet add package FlagstoneUI.Integrations.MCT --version 0.0.1-preview1

dotnet add package FlagstoneUI.Themes.Material --version 0.0.1-preview1

What Does It Look Like?

<!-- Direct styling - this is FlagstoneUI core -->
<FsButton 
    Text="Click Me" 
    BackgroundColor="#6750A4" 
    CornerRadius="12" />

<!-- Theme-based styling with implicit styles -->
<FsButton Text="Submit" />  <!-- Uses implicit style from theme -->

<!-- Entry with validation -->
<FsEntry 
    Placeholder="Email"
    CornerRadius="8"
    BorderBrush="#2196F3"
    BorderWidth="2">
    <FsEntry.Behaviors>
        <ValidationBehaviorAdapter
            ValidStyle="{StaticResource ValidStyle}"
            InvalidStyle="{StaticResource InvalidStyle}"
            Behavior="{EmailValidationBehavior}"
            Flags="ValidateOnValueChanged" />
    </FsEntry.Behaviors>
</FsEntry>

<!-- Card container -->
<FsCard
    BackgroundColor="#FAFAFA"
    CornerRadius="12"
    Padding="16">
    <Label Text="Card Content" />
</FsCard>

If not using implicit/global namespaces, prefix controls as: <fs:FsButton>...</fs:FsButton>

How It Works

1. Enhanced Controls Purpose‑built controls that expose full visual control from shared code.

2. Standard .NET MAUI Styling Use inline values, explicit styles, implicit styles, or StaticResource/DynamicResource — all valid approaches.

3. Themes Resource dictionaries that apply consistent design across your app.

4. Flexibility Use direct values for simple cases, app resources for reusability, or design tokens for consistency — choose what fits your project.

Development Status

Available

• FsButton, FsEntry, FsCard, FsEditor
• Unified styling plane for .NET MAUI
• Material theme (example implementation)
• Sample app with multiple theme examples
• Community Toolkit integration
• Full documentation

Coming Soon

• Additional controls (labels, lists, navigation)
• More theme examples
• Theme conversion tools

See the roadmap.

Project Structure

flagstone-ui/
├── src/
│   ├── FlagstoneUI.Core/              # Core controls + styling surface
│   ├── FlagstoneUI.Themes.Material/   # Material theme example
│   └── FlagstoneUI.Blocks/            # Planned: reusable UI building blocks
├── samples/
│   ├── FlagstoneUI.SampleApp/         # Showcase
│   └── FlagstoneUI.ThemePlayground/   # Theme experimentation
├── docs/                              # Documentation
└── tools/                             # Theme converters and utilities

The Blocks project (planned) will offer prebuilt forms, layouts, and workflows — optional extensions built on FlagstoneUI controls.

Contributing

This project is still early — your feedback genuinely shapes its direction.

Most important of all: Tell me whether this is useful, or if you think the entire idea is misguided. Honest critique is just as valuable as enthusiasm.

Ways to help

• Try the sample apps and share what worked (or didn’t)
• Tell me why you would or wouldn’t use this
• Report bugs or suggest features
• Submit PRs
• Create and publish themes
• Improve documentation

Open a Discussion or reach out to @matt-goldman.

License: MIT Status: Experimental Compatibility: .NET 10 + MAUI