android-app | Official ProtonVPN Android app | VPN library

the Android Gradle Plugin documentation still says classpath 'com.android.tools.build:gradle:4.2.0' instead of 7.0.1.

You need to read further down the page, to this and this. That table is only relevant for pre-7.0.0 versions.

Is this a bug in Android Gradle Plugin 7.0.1?

Quite possibly. Or, perhaps beyond, as the Instantiatable Lint check has a history of problems.

If your scenario does not match one of those three August 2021 bugs, and you are in position to provide a reproducible test case, file a fresh issue! Beyond that, if a clean-and-rebuild is not clearing up your problem, you might need to simply disable the Instantiatable Lint check for the time being by adding the following to all of your build.gradle files at the application or library level (i.e. all except your project-level build.gradle):

I'm not sure about the failure to connect specifically to local addresses over bluetooth, but you can request a specific network and set it as the default.

https://github.com/square/okhttp/issues/2404

or specify it using a socketfactory

https://programmer.ink/think/the-implementation-of-okhttp-multi-network-communication.html

I think that your code should looks like this:

Navigation routes are equivalent to urls. Generally you're supposed to pass something like id there.

When you need to pass a url inside another url, you need to encode it:

After a bit of digging and exploring some open source projects, I found the solution for the above issue. Initially, I was using the distributionUrl=https\://services.gradle.org/distributions/gradle-7.0.2-bin.zip as my Gradle version in gradle-wrapper.properties but to fix the issue I updated the Gradle version to 7.3.2

So changing the distribution URL to distributionUrl=https\://services.gradle.org/distributions/gradle-7.3.2-all.zip fixed the issue for me

The purpose of it is to be able to send that key everytime I call a webservice that I've made, so I'm sure (or almost sure) that the call comes from the original app that I'm making and that will be published on the Play Store, and not from elsewhere.

This is a very hard task to achieve, but not impossible one and here is where one needs to make a deep dive in mobile API security and understand the mechanics behind it.

It's fundamental to have a clear understand between the difference of who is in the API request versus what is making that API request, otherwise any security solution you may devise/use may not have the intended results.

I wrote a series of articles around API and Mobile security, and in the article Why Does Your Mobile App Need An Api Key? you can read in detail the difference between who and what is accessing your API server, but I will extract here the main takes from it:

The what is the thing making the request to the API server. Is it really a genuine instance of your mobile app, or is it a bot, an automated script or an attacker manually poking around your API server with a tool like Postman?

The who is the user of the mobile app that we can authenticate, authorize and identify in several ways, like using OpenID Connect or OAUTH2 flows.

So, you need to think about the who as the user your API server will be able to Authenticate and Authorize access to the data, and you need to think about the what as the software making that request in behalf of the user.

I also don't want to store my key in my code, also because it could easily be retrieved via reverse engineering.

That's very true, it's more or less easily achieved depending on the method used to hide the API key, as per the ones you mention:

I've also checked the other methods explained here, but they look like the API key could quite easily be retrieved thanks to reverse engineering.

No matter how secure the API key has been stored, be it in the Android Keystore, encrypted, obfuscated, etc, at some point the API key will need to be in plain text to be sent on the API request header, and in this moment it will be vulnerable to be extracted via static reverse engineering, via a MitM attack or via an instrumentation framework

I have wrote the article How to Extract an API key from a Mobile App with Static Binary Analysis to illustrate how easy it can be done:

The range of open source tools available for reverse engineering is huge, and we really can't scratch the surface of this topic in this article, but instead we will focus in using the Mobile Security Framework(MobSF) to demonstrate how to reverse engineer the APK of our mobile app. MobSF is a collection of open source tools that present their results in an attractive dashboard, but the same tools used under the hood within MobSF and elsewhere can be used individually to achieve the same results.

During this article we will use the Android Hide Secrets research repository that is a dummy mobile app with API keys hidden using several different techniques.

I also wrote another article to achieve it during runtime, Steal that Api Key with a Man in the Middle Attack:

In order to help to demonstrate how to steal an API key, I have built and released in Github the Currency Converter Demo app for Android, which uses the same JNI/NDK technique we used in the earlier Android Hide Secrets app to hide the API key.

So, in this article you will learn how to setup and run a MitM attack to intercept https traffic in a mobile device under your control, so that you can steal the API key. Finally, you will see at a high level how MitM attacks can be mitigated.

An instrumentation framework can also be used during runtime to hook into the code that uses the API key in order to extract it. For example with the popular Frida framework:

Inject your own scripts into black box processes. Hook any function, spy on crypto APIs or trace private application code, no source code needed. Edit, hit save, and instantly see the results. All without compilation steps or program restarts.

So, no matter what it's done to secure the API key, once it's on the API request will be vulnerable to be extracted.

Anything that runs on the client side and needs some secret to access an API can be abused in different ways and you can learn more on this series of articles about Mobile API Security Techniques. This articles will teach you how API Keys, User Access Tokens, HMAC and TLS Pinning can be used to protect the API and how they can be bypassed.

I recommend you to read this answer I gave to the question How to secure an API REST for mobile app?, especially the sections Hardening and Shielding the Mobile App, Securing the API Server and A Possible Better Solution.

The possible best solution for your problem is known by Mobile App Attestation, that will let your backend know that what is making the request is indeed a genuine and untampered version of your mobile app, as you wish to achieve:

The purpose of it is to be able to send that key everytime I call a webservice that I've made, so I'm sure (or almost sure) that the call comes from the original app that I'm making and that will be published on the Play Store, and not from elsewhere.

In any response to a security question I always like to reference the excellent work from the OWASP foundation.

OWASP API Security Top 10

The OWASP API Security Project seeks to provide value to software developers and security assessors by underscoring the potential risks in insecure APIs, and illustrating how these risks may be mitigated. In order to facilitate this goal, the OWASP API Security Project will create and maintain a Top 10 API Security Risks document, as well as a documentation portal for best practices when creating or assessing APIs.

OWASP Mobile Security Project - Top 10 risks

The OWASP Mobile Security Project is a centralized resource intended to give developers and security teams the resources they need to build and maintain secure mobile applications. Through the project, our goal is to classify mobile security risks and provide developmental controls to reduce their impact or likelihood of exploitation.

OWASP - Mobile Security Testing Guide:

The Mobile Security Testing Guide (MSTG) is a comprehensive manual for mobile app security development, testing and reverse engineering.

The relationship between your activity and chrome custom tabs depends on the launchMode. You can launch the custom tab in current stack or a new stack.

The problem that when you change the dark mode, the activity restarts with the default settings (default language), so you need to explicitly force the user's language.

But setting that explicitly every time you change the dark mode could be boilerplate, and this also could require a one more restart of the activity to apply the language.

Instead of that, you can use a customized ContextWrapper where you can apply the preferred language at the very beginning of your app in the attachBaseContext() activity callback by wrapping this customized ContextWrapper:

The custom context wrapper:

are you looking for this:

call to prompt for FlexibleUpdate, this will pop up the google prompt and the user can tap "Install" from there. It seems to handle the download/install all in one and i dont have to do the "reload" snackbar step the docs were talking about.