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.NET MAUI › XAML & Markup Extensions

What do OnPlatform and OnIdiom do?

Beginner

Answer

OnPlatform supplies different values per platform (iOS/Android/WinUI/MacCatalyst); OnIdiom supplies values per device type (Phone/Tablet/Desktop/TV/Watch). They're used inline in XAML to tweak sizes, margins, or resources without code-behind branching.
<StackLayout Padding="{OnPlatform iOS='20,40,20,20',
                                  Android='20'}"
             Spacing="{OnIdiom Phone=8, Desktop=16}" />
Real-world example Extra top padding accommodates the iOS status bar while Android uses uniform padding, and spacing grows on desktop.

Common follow-ups: OnPlatform vs OnIdiom? | Can they return complex values?

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All 6 XAML & Markup Extensions questions