android-intents | small library which will save

You can not change marker in Google Maps Intents. if you want to show custom marker you have to use google maps api in Application and draw you own layer over the map.

if you want to use google map api in react native use react-native-maps it provide native map components.

You can use the launchnavigator plugin. It allows you to call launchnavigator.navigate which will open the available apps that can be used (both Android and iOS). You can also specify a specific app as well.

But what kind of implicit intent is being created here?

Um... an ACTION_VIEW Intent, to view the requested URL.

can I think of Android as going through all the classes in my phone and seeing which one has the intent filter that can possibly handle the data and creating the intent structure to start this class that it found?

Activities are registered in the manifest. The OS basically has a database of all registered activities and their details, and it uses that database to find candidates for any given implicit Intent.

Does it simply choose the default or ask the user to choose what app it wants to run in on?

That depends on a variety of factors, including:

• Whether the user chose a default handler for that sort of Intent (e.g., chose a default Web browser)

• Whether you wrap the Intent using Intent.createChooser() to force a chooser

• Whether an app has registered an app link for the URL

If the intent has already been linked to a class to start, why bother with intent.resolveActivity(getPackageManager()) at all?

Because there may be zero activities to handle the Intent. Even for something as common as a Web browser, the specific user might not have access to a browser app (secondary user profiles, etc.). If you try starting an activity, and there is no match, you get an ActivityNotFoundException, so this check is trying to avoid such an exception.

but would I be sort-of correct in saying that Intent.ACTION_VIEW runs intent.resolveActivity(getPackageManager()) or another function that does similar and somehow incorporates the class it returns into my intent?

Not really. It would be more correct to say that resolveActivity() queries the database that I mentioned to see what would handle the Intent, if anything.

what is inside the package manager class?

A little bit of Java code. It is mostly an IPC gateway to a core OS process, serving to query the database of installed apps, their capabilities, etc.

Using getExtras() method, I discovered there is only one extra: android.intent.extra.TEXT, which contains the URL of the Instagram publication that is shared from Instagram to my app.

So, to get it, write: String url = intent.getStringExtra("android.intent.extra.TEXT");

Waiting for confirmations...! :) In particular: is there any legal mean to get the image (or video), the comments and the legend of the publication (the legend is the text the Instagramer write while posting the image or video and it appears just below the media, and above the comments)?

Use a geo: URI, as stated here. Disappointingly, this does not provide a mechanism for launching directly into turn-by-turn navigation.

I've tried Directions URL on my android mobile phone and I see there's an options icon underneath the directions search boxes.

Since V3 Google Maps Directions API support up to 23 waypoints (excluding the origin and destination) when calculating routes:

https://maps.googleapis.com/maps/api/directions/json?origin=sydney,au&destination=perth,au&waypoints=via:-37.81223%2C144.96254%7Cvia:-34.92788%2C138.60008&key=YOUR_API_KEY

So, you can draw polyline with up to 23 points and send they coords in request.

UPDATE: Please see this tutorial.

UPDATE 2:

Example opening navigation mode of Google Maps app for route Tel-Aviv to Jerusalem via Kiryat Malakhi, Beit+Guvrin and geopoint (31.696342, 35.011337) via Intent:

Before doing the share intent I would ask the users their instagram username and save it in your server database. Then, at the end of the event I would use the Python Client for Instagram API to retrieve all photos containing your hashtag and photo owner username. Then make a simple sum of photos for each user to know the winner.