[Xamarin.Android.Build.Tasks] Link Resource Nested Types from assemblies

[dellis1972]

The idea is to remove the Resource class NestedTypes from the final
linked assemblies in release mode. We do this by examining all the
locations where the fields are used and replacing those IL calls with a
call which specifies the actual resource id directly. This will remove
the need to call global::Android.Runtime.ResourceIdManager.UpdateIdValues();
completely. It will also allow us to completely remove the Resource
class sub classes. Due to an odd linker failure we cannot completely
remove the Resource class itself. However it will be completely empty.

As mentioned the call to UpdateIdValues will no longer be required.
This should reduce startup time slightly. One thing to note is this will
only be true for Release apps when enabled. Debug apps will still
call UpdateIdValues. This is due to the time is takes to run
the Linker Step. Applying this to a Debug build would effect the build
times during development.

A new MSBuild property AndroidLinkResources has been added to control
this feature. It is turned off by default for now.

This seems to save between 100-280kb for an apk. This is dependent on
how many assemblies are Android assemblies and contain or use Resources.

Xamarin.Forms base app apkdiff results

Size difference in bytes ([*1] apk1 only, [*2] apk2 only):
  -          10 assemblies/Mono.Android.dll
  -       4,001 assemblies/Xamarin.Essentials.dll
  -      45,426 assemblies/Xamarin.Forms.Platform.Android.dll
  -     102,839 assemblies/formstest.Android.dll
Summary:
  +           0 Other entries 0.00% (of 887,808)
  +           0 Dalvik executables 0.00% (of 3,341,152)
  -     152,276 Assemblies -3.23% (of 4,709,077)
  +           0 Shared libraries 0.00% (of 41,693,796)
  -     151,552 Package size difference -0.73% (of 20,820,695)

Maps sample apkdiff results

Size difference in bytes ([*1] apk1 only, [*2] apk2 only):
  -           4 lib/armeabi-v7a/libxamarin-app.so
  -          14 assemblies/Mono.Android.dll
  -       4,757 assemblies/Xamarin.Essentials.dll
  -      46,051 assemblies/Xamarin.Forms.Platform.dll
  -      47,586 assemblies/Xamarin.Forms.Platform.Android.dll
  -      48,470 assemblies/Xamarin.Forms.Maps.Android.dll
  -     135,589 assemblies/FormsMapsSample.Android.dll
Summary:
  +           0 Other entries 0.00% (of 1,137,209)
  +           0 Dalvik executables 0.00% (of 2,519,972)
  -     282,467 Assemblies -5.51% (of 5,123,833)
  -           4 Shared libraries -0.00% (of 41,843,596)
  -     282,624 Package size difference -1.34% (of 21,075,664)

[dellis1972]

@radekdoulik this is a work in progress, but if you have any advice on how to do this more efficiently please feel free to comment.

[jonathanpeppers]

Might want to wait on: xamarin/Xamarin.Forms#13176

Is there a way to make a test for this?

• Xamarin.Forms app using <Image Source="foo" /> where foo is AndroidResource
• Launch the app, verify the image is displayed?

[jonpryor]

@jonathanpeppers wrote:

Might want to wait on: xamarin/Xamarin.Forms#13176

xamarin/Xamarin.Forms#13176 has been merged. How do we know when we can rely on it?

[jonathanpeppers]

xamarin/Xamarin.Forms#13176 has been merged. How do we know when we can rely on it?

@jonpryor the [Obsolete] messages say:

[Obsolete("GetDrawableByName(string) is obsolete as of version 4.8. "
			+ "Please use GetDrawableId(string, context) instead.")]

I see the change in if I download & ilspy Xamarin.Forms 5.0.0.2012 but not 4.8.0.1821.

So maybe this is only in Xamarin.Forms 5.0 and higher.

[dellis1972]

/azp run

[azure-pipelines]

Azure Pipelines failed to run 1 pipeline(s).

[jonathanpeppers]

Otherwise, LGTM 👍

[jonpryor]

Squash-and-merge:

Summary:

[Xamarin.Android.Build.Tasks] Add $(AndroidLinkResources) (#5317)

commit message:

The generated `Resource` class in `Resource.designer.cs` can be quite
large.

When doing "Release" builds, update the linker to *remove* the
`Resource` class and its nested types.  We do this by examining all
the locations where the fields are used and replacing those IL calls
with a call which specifies the actual resource id value directly.

This will remove the need to call
`global::Android.Runtime.ResourceIdManager.UpdateIdValues();` from
the static constructors in the `Resource` class and its nested types,
which will improve app launch times (as `UpdateIdValues()` involves
Reflection, which is not "fast").

Due to an odd linker failure we cannot completely remove the
`Resource` class itself.  It *will* be completely empty.

"Debug" builds will *not* remove the `Resource` type, and will retain
the call to `UpdateIdValues()`, in order to ensure that app rebuild
and redeploy times are as fast as possible.

The new `$(AndroidLinkResources)` MSBuild property has been added to
control this feature.  It is disabled by default for now.

`$(AndroidLinkResources)`=True appears to save between 100-280kb for
an `.apk`.  This is dependent on how many assemblies are Android
assemblies and contain or use Resources.

Xamarin.Forms base app `apkdiff` results

	Size difference in bytes ([*1] apk1 only, [*2] apk2 only):
	  -          10 assemblies/Mono.Android.dll
	  -       4,001 assemblies/Xamarin.Essentials.dll
	  -      45,426 assemblies/Xamarin.Forms.Platform.Android.dll
	  -     102,839 assemblies/formstest.Android.dll
	Summary:
	  +           0 Other entries 0.00% (of 887,808)
	  +           0 Dalvik executables 0.00% (of 3,341,152)
	  -     152,276 Assemblies -3.23% (of 4,709,077)
	  +           0 Shared libraries 0.00% (of 41,693,796)
	  -     151,552 Package size difference -0.73% (of 20,820,695)

Maps sample `apkdiff` results

	Size difference in bytes ([*1] apk1 only, [*2] apk2 only):
	  -           4 lib/armeabi-v7a/libxamarin-app.so
	  -          14 assemblies/Mono.Android.dll
	  -       4,757 assemblies/Xamarin.Essentials.dll
	  -      46,051 assemblies/Xamarin.Forms.Platform.dll
	  -      47,586 assemblies/Xamarin.Forms.Platform.Android.dll
	  -      48,470 assemblies/Xamarin.Forms.Maps.Android.dll
	  -     135,589 assemblies/FormsMapsSample.Android.dll
	Summary:
	  +           0 Other entries 0.00% (of 1,137,209)
	  +           0 Dalvik executables 0.00% (of 2,519,972)
	  -     282,467 Assemblies -5.51% (of 5,123,833)
	  -           4 Shared libraries -0.00% (of 41,843,596)
	  -     282,624 Package size difference -1.34% (of 21,075,664)