.NET MAUI Conditional Compilation

When you need to call a feature that .NET MAUI hasn't abstracted (or you need a specific native behavior), you use Conditional Compilation with #if directives. This tells the compiler to only include that block of code when building for that specific platform.

1. Common Platform Symbols

The compiler recognizes these built-in symbols:

• ANDROID: For Android devices.
• IOS: For iPhone / iPad.
• MACCATALYST: For macOS apps built with MAUI.
• WINDOWS: For Windows (WinUI3).
• TIZEN: For Samsung devices.

2. Basic Syntax Example

You can use these inside any .cs file. The code inside inactive blocks is completely ignored by the compiler for that build target.

public void ShowPlatformMessage()
{
#if ANDROID
    // This code only exists in the Android APK
    var message = "Hello from Android Native!";
#elif IOS
    // This code only exists in the iOS IPA
    var message = "Hello from iOS Native!";
#else
    var message = "Hello from an unknown platform!";
#endif

    Console.WriteLine(message);
}
    

3. Accessing Native APIs

The real power comes from accessing native classes (like Android.App or UIKit.UIView) directly inside your shared logic.

public string GetSystemVersion()
{
#if ANDROID
    return Android.OS.Build.VERSION.Release;
#elif IOS
    return UIKit.UIDevice.CurrentDevice.SystemVersion;
#elif WINDOWS
    return Microsoft.Windows.System.UserProfile.GlobalizationPreferences.Languages[0];
#else
    return "Not available";
#endif
}    

4. Using it in MauiProgram.cs

This is the most common place to use #if for configuring platform-specific lifecycle events or handlers.

builder.ConfigureLifecycleEvents(events =>
{
#if ANDROID
    events.AddAndroid(android => android
        .OnCreate((activity, bundle) =>
            Log.Info("TAG", "Android Created!")));
#elif IOS
    events.AddiOS(ios => ios
        .FinishedLaunching((app, options) =>
        {
            Console.WriteLine("iOS Launched!");
            return true;
        }));
#endif
});
    

Directives vs Platform Folders

While #if directives are great for quick fixes, MAUI also supports Partial Classes and the Platforms Folder (Platforms/Android/, Platforms/iOS/, etc.).

• Use #if directives when the platform-specific code is small (1–10 lines) and lives inside a shared method.
• Use the Platforms folder when writing large amounts of native logic or custom handlers to keep your shared files clean.

🧩 Best Practices

• Keep shared logic in cross-platform code and isolate platform-specific code behind #if.
• Use Dependency Injection or partial classes if platform-specific code grows large.
• Avoid scattering #if everywhere — centralize platform checks for maintainability.
• Test on each platform to ensure the directives behave as expected.

🎯 When to Use

• Accessing native APIs not covered by MAUI Essentials.
• Handling UI differences (like status bar height).
• Managing file paths or OS-specific features.

Think of #if directives as a safety valve: you use them only when you must dip into platform-specific territory, while keeping most of your app cross-platform