xamarin/Xamarin.Forms

[Xaml] Missing platform/idiom value in OnPlatform/OnIdiom causes ArgumentNullException when type is x:BindingBase

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#5,629 opened on Mar 20, 2019

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Description

Description

Missing platform/idiom value in OnPlatform/OnIdiom causes ArgumentNullException when type is x:BindingBase.

Steps to Reproduce

  1. for example: <StackLayout> <StackLayout.IsEnabled> <OnPlatform x:TypeArguments="BindingBase" iOS="{Binding Source=False}"/> </StackLayout.IsEnabled> </StackLayout>

  2. run it on any non-iOS platform.

Expected Behavior

don't try to set any binding or value for IsEnabled on any other platform than iOS.

Actual Behavior

[ERROR] FATAL UNHANDLED EXCEPTION: System.ArgumentNullException: Value cannot be null. Parameter name: binding at (wrapper dynamic-method) System.Object.7(intptr,intptr,intptr) at (wrapper native-to-managed) System.Object.7(intptr,intptr,intptr)

Basic Information

  • Version with issue: 3.6.0
  • IDE: VS 15.9.8
  • Platform Target Frameworks: Xamarin.Forms

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.
2
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
Basic C# and XAML knowledgeFamiliarity with Xamarin.Forms binding system
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65
Research direction
The issue is a bug in the OnPlatform markup extension when used with BindingBase. The fix likely involves checking for null binding in the platform resolution logic. Search for the implementation of OnPlatform in the Xamarin.Forms source code, likely in the Xaml parsing or markup extensions directory. Look at similar issues or PRs that may have addressed this pattern. The file to examine is probably OnPlatformExtension.cs or similar. Ensure that when a platform specific value is missing for a given platform, it does not attempt to apply a null binding.