Is it useful to learn native android development, when som many web tech. can be used to make apps?

I am not a mobile developer myself, but I can see alot of reasons why it is good to learn Android. This is just my opinion:

• Java is one of the most used languages in the world, even outside of Android. So you can bring alot of the things you learn to a different platform even if you decide not to persue a career in Android;

• Many of the concepts you learn you can also use in different languages;

• The more experience you get the less important knowledge of a specific language is as you will be faster to get comfortable with new languages and frameworks;

• Using JS-frameworks for building mobile apps can be a pretty solid approach, but one of the downsides of JS is the sheer amount of libraries there are, and you never know if and for how long these libraries are supported.

That said

• Using JS-frameworks like React Native allow you to write iOS and Android-apps with reuse of alot of code, which means you have just 1 app to maintain, rather than 1 for Android and 1 for iOS;

If you have started, I would suggest to finish it. I myself have changed languages and frameworks so often, I regret doing so. Because it took me longer to become a decent developer.