LayoutBindings: 'PreserveAttribute' is obsolete warnings

[rgroenewoudt]

Android application type

Android for .NET (net6.0-android, etc.)

Affected platform version

VS2022 17.3.6

Description

We are using a lot of AndroidBoundLayout in our app but this results in 2 warnings per layout file:

warning CS0618: 'PreserveAttribute' is obsolete: 'Please use [System.Diagnostics.CodeAnalysis.DynamicDependencyAttribute]'

[global::Android.Runtime.PreserveAttribute (Conditional=true)]
public AboutSequriX (
	global::Android.App.Activity client,
	global::Xamarin.Android.Design.OnLayoutItemNotFoundHandler itemNotFoundHandler = null)
		: base (client, itemNotFoundHandler)
{}

[global::Android.Runtime.PreserveAttribute (Conditional=true)]
public AboutSequriX (
	global::Android.Views.View client,
	global::Xamarin.Android.Design.OnLayoutItemNotFoundHandler itemNotFoundHandler = null)
		: base (client, itemNotFoundHandler)
{}

We would like to get to 0 build warnings :)

Steps to Reproduce

Did you find any workaround?

No response

Relevant log output

No response

[dellis1972]

Those look like they are coming from the Xamarin.Android.Support.Design Nuget Package.
I believe the recomendation now is to upgrade to use AndroidX rather than the old packages.
So you will need to migrate the code away from the old Support libraries to AndroidX.

See https://learn.microsoft.com/en-us/xamarin/android/platform/androidx for more details.

The PreserveAttribute is going to be removed in a future version of .net so migrating is the best option.

[rgroenewoudt]

@dellis1972 I don't have any nuget packages Xamarin.Android.Support or any referencing it. Only AndroidX.

Example project. I created a new .NET 6 Android project, changed activity_main.xml to AndroidBoundlayout and added an ID.
AndroidApp2.zip

1>C:\git\AndroidApp2\AndroidApp2\obj\Debug\net6.0-android\generated\Binding.activity_main.g.cs(12,4,12,45): warning CS0618: 'PreserveAttribute' is obsolete: 'Please use [System.Diagnostics.CodeAnalysis.DynamicDependencyAttribute]'
1>C:\git\AndroidApp2\AndroidApp2\obj\Debug\net6.0-android\generated\Binding.activity_main.g.cs(19,4,19,45): warning CS0618: 'PreserveAttribute' is obsolete: 'Please use [System.Diagnostics.CodeAnalysis.DynamicDependencyAttribute]'

[dellis1972]

Ah. Are you using LayoutBindings?

[dellis1972]

Ignore that, yes you are :) sorry.

OK, that is where the issue is then.

[rgroenewoudt]

I would guess that there would need to be an if added to support both classic with PreserveAttribute and .NET 6 with DynamicDependencyAttribute.
https://github.com/xamarin/xamarin-android/blob/ab6712a48e4b93e9c3d605c7b393814d477e2bc8/src/Xamarin.Android.Build.Tasks/Tasks/GenerateLayoutBindings.CSharpBindingGenerator.cs#L221

A additional property would be probably be needed to feed the MsBuild task, perhaps UsingAndroidNETSdk?
https://github.com/xamarin/xamarin-android/blob/ab6712a48e4b93e9c3d605c7b393814d477e2bc8/src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets#L1152

[dellis1972]

DynamicDependencyAttribute works in the reverse manner to the old PreserveAttribute. The old system you placed the attribute at the code you wanted to preserver. The new DynamicDependencyAttribute you have to place it where the type is consumed. So we need to figure out the best way to deal with this without requiring the user to add the DynamicDependencyAttribute to the activity where its used.

[rgroenewoudt]

Is the attribute even needed? This is the C# binding which is used by the developer so if unused constructors are removed it shouldn't be a problem?

The file should also contain the autogenerated comment so any warnings would be ignored.

[jpobst]

The file should also contain the autogenerated comment so any warnings would be ignored.

A little more information on that:

• [generator] Mark generated .cs files as such so Roslyn analyzers can choose to ignore them. java-interop#1052.
• Generated files (e.g, Java.Interop.__TypeRegistrations.cs) should mark themselves as auto-generated java-interop#1051 (comment)