xamarin/Xamarin.Forms

XF 3.6 Material Setting in App.Xaml requires default value

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#5,733 opened on Mar 28, 2019

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Description

I love Xamarin Forms...now on to the bug/feature?...

In my app.xaml I create a Style for ContentPages to apply Material to only iOS pages due to a bug in Android Material in XF 3.6 preventing me from using it in Android for now:

<Style TargetType="ContentPage" ApplyToDerivedTypes="true"> <Setter Property="Visual"> <Setter.Value> <OnPlatform x:TypeArguments="IVisual" iOS="Material" /> </Setter.Value> </Setter> </Style>

Running in Android throws the error:

System.ArgumentException: Value was an invalid value for Visual Parameter name: value

Adding the Default to Android this fixes it, but shouldn't default be default?

<OnPlatform x:TypeArguments="IVisual" iOS="Material" Android="Default" />

Expected Behavior

Default values shouldn't need to be set?

Actual Behavior

Default is required

Basic Information

  • Android: 9

Contributor guide

Tech stack
csharp
Domain
mobile
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Familiarity with Xamarin.Forms and C#Understanding of XAML markup extensionsKnowledge of OnPlatform and Visual property
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
Investigate the OnPlatform markup extension in Xamarin.Forms source code to understand how it resolves values per platform. The issue is that when only iOS is specified, Android gets an invalid value. The fix likely involves setting a default value for platforms not specified, or modifying the Visual property's validation to treat null as Default. Check the OnPlatform class in Xamarin.Forms.Core or Xamarin.Forms.Xaml for the logic that provides the value, and consider adding a default fallback.
XF 3.6 Material Setting in App.Xaml requires default value · xamarin/Xamarin.Forms#5733 | Good First Issue