Develop Reference

how to save my app preference and retrieve them after re-install or change of device

I'm new to app dev...
I read somewhere in the doc: "...In most cases you want to use SharedPreferences as it is automatically backed up and migrated to new devices..."
On first install my app saves a few settings with SharedPreferences. It works great but if I uninstall the app or install it on another device the preference settings are lost.
How can I have these settings saved online within google somehow to be able to retrieve them if the user changes his phone or similar...
Could someone point me in the right direction ?

I read somewhere in the doc: "...In most cases you want to use SharedPreferences as it is automatically backed up and migrated to new devices..."
Your words "backed up and migrated to new devices" is nowhere written nor its true.
We use SharedPreferences in order to minimise the database operations, its like keeping variables handy.
On first install my app saves a few settings with SharedPreferences. It works great but if I uninstall the app or install it on another device the preference settings are lost.
If you wants to store or remember the device dependent settings, use device id / imei_id and store it on your web server mysql database
Even if user uninstalls app from the device and installs again anytime in future, make a call with async task to server by sending deviceid / imei_id and fetch its settings from mysql database and show it.
How can I have these settings saved online within google somehow to be
able to retrieve them if the user changes his phone or similar...
If user changes device, you can do nothing.
One way is, keep public device_id levels keys on server.
If user changes device and uses that key, then show him a response, this key is assigned to another device, but if you are the same, wait for our support
Call him, confirm he is the same old user with new device and delete his old entry from mysql and assign old key to the new device entry
Or use OTP SMS system to identify already existing customers with unique phone numbers
If OTP authentication code is correct then fetch settings for that user from the server, delete old mysql entry, modify new entry with old key and mobile number
This should be the your direction
Edit : 2 ##
I was hoping an easier solution exist but....
There is no short cuts for developers till the date, and it will be never.
Why, no short cuts / easy ways ?
Any device ( mobile, desktop / laptop / any AI device ) which is operated by a system software, is able to perform the tasks as per it is structured.
Ex : android is java based, obviously you can Make javascript based apps, but it is the extensions to the existing system, Android still has the base of Java virtual machine. ( Dalvic / Malvic like )
So, it is always better to use native java
Yes, Kotlin is best option now a days and better than hybrid approach
Every way has its own advantages, disadvantages
If you are developer, should go with native approach
Now your java code never knows, which version it is running on, so you have to, check android versions programming wise, and decide the flow for above Marshmallow & below marshmallow too, and it is explicitly done by developer by coding.
Ex, once user registers, he never shown please register again screen, it is not the magic, nor google, nor, java, nor android does anything, developer has decided, planned, architectured, designed, coded, tested that.
Even developers needs to take care of exceptions, you need to handle it in order to save your app from crashing.
In short developer is god, who creates his own universe, and everything is pre-planned and verified thats it.

You should use allowBackup = "true" in your manifest file. More details can be found here: AutoBackup

Data storage option that best suits for my android app purpose

I am creating an android app that can be used by common users and also admin.
Suppose, if admin adds a new place name, that name should be added to database and when common user uses the app, he should be able to see the place name that is added.
I used MySqlLite database. But the problem is that if the app is uninstalled all data is lost. So I want some persistent data storage in which all the places that are added by admin are saved permanently.
Regards,
Sindhu

With the data being needed across multiple devices, your only option is to create/use a backend API.
Parse would have been a good choice but since that is getting shut down soon then it wouldn't be wise to use that.
Take a look at these alternatives here
You could also write one yourself, but unless you have some experience in that sort of thing then it will take some time to learn.

Android: Sharing Data between multiple applications

I have a requirement, wherein I have 4 android apps, which are sending notifications to a user, at a fixed time of the day. A user could have one, or more of these apps installed on his phone.
I want only one of the apps(any one) to show this notification to the user, because multiple apps popping up notifications is a bad user experience.
For this I need to share some data across the apps.
I was thinking of a mutex/lock based approach, the problem is, where do I store it?
Problems:
Shared Prefs: I don't know which app wrote the data first, and from which app's context should I read.
SQLite: Same Problem as above and app uninstalls need to be handled and SD card might be missing
Server: Mostly offline app, dont want to add internet permission just for this
I see files at a common location as the only way to store this information.
Is there any better way

As you said that the easiest ways is with file,
I did this before and i too wasn't able to find more easy way.
when you show the notification first time then Just make a new file anywhere which can be common for any app and then check if file is exist.
if it exist then don't show the notification and if not then show and make file again, also remember to delete the file from any of your app when day changed, use AlarmManager for this.
hope it helps.

Creating event in calendar only once when App is installled

I am developing a Application which will create events in calendar. Events should get created only once when my application is installed and opened. I tried with using Shared preferences. But when i clear my app data, shared preferences were also getting cleared.
Please let me know how to do this.

Although Shared preferences is usually used for the use case like yours, but since you wants to be guarded against "Clear Data", You may create an empty file as an alternative.
You can check (before creating a Cal.event) if your file(whose exact name and location is only known to you) exist.
Obviously, there are many situations with this approach against which you need to protect.
1.what if user removes this file?
2.if you chose to save file on SD-card, what if sdcard is removed?
In case, if you do not want to rely on Device and data saved on device, and if your app can communicate with Server, then you can maintain this installation history information "online". Then, invoke a network call to query "installation history" info.
For this method to work, you also needs to track on which device and user, the installation was done previously.

Completely uninstall and reinstall Android app on update?

I want to publish a new version of my app. But I want it to reinstall again.
Like first uninstall and then install(like first time installation). Is there anyway that I can do it? Or force users to first uninstall the app?

If you sign the new apk with a different key, users will hit an error when they try to upgrade an existing installation. That’s probably the easiest way to do it without changing the package name.

As Jens said you can't do this really unless you reinstall with a different package name (not a good idea either.) You have to detect your version and manually reset your preferences etc. if you need to. This is a pretty annoying feature of android. I've been developing a mapping application that has the exact same problem with storing some of the background data.
You can usually check where your preferences get created for the first time. A lot of people do a if(preference !=null) to set them up, since in a pre-installed app you already have that preference in the bundle it will not update or generate a new one.
Try setting the preference checker to be if(preference != newValueOfPreference)
If that's not how your bundle data is generated on install you'll have to find out how it is generated and get at that hook.