set namespace in build.gradle

[tarunrajput]

Summary

Resolves #392

Setting the namespace via a source AndroidManifest.xml's package attribute is deprecated.
Please instead set the namespace (or testNamespace) in the module's build.gradle file, as described here:
https://developer.android.com/studio/build/configure-app-module#set-namespace

More context: react-native-community/discussions-and-proposals#671

[tarunrajput]

@jacobp100 , @janicduplessis could you please take a moment to review the PR?

[jacobp100]

I’m not too sure on this stuff, so I’ll defer to Janic for this

[peterlazar1993]

Please consider react-native-community/discussions-and-proposals#671 (comment)

[janicduplessis]

Thanks!

[ivanignatiev]

I think removal of package in manifest is optional for backward compatibility.

You also need to add android.buildFeatures.buildConfig true otherwise it will fail:

FAILURE: Build failed with an exception.

* What went wrong:
A problem occurred configuring project ':react-native-safe-area-context'.
> com.android.builder.errors.EvalIssueException: defaultConfig contains custom BuildConfig fields, but the feature is disabled.
  To enable the feature, add the following to your module-level build.gradle:
  `android.buildFeatures.buildConfig true`

BUILD FAILED in 4s
error Failed to install the app.

Also, please take a look on issue #439

Thank you!