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How can I change content of my app after it is published without updating version?

I want to make an android app that will display mess menu of hostel. The menu will be changing every week so how can I change content of TextView once it is installed in user's phone .I considered WebView but I want better alternative . I think I need some cloud based service here . What are some good resources to achieve this.

Just do a Simple REST API and then every time you start your app call your api to retrieve the information, for example
yourdomaing.com/api/menu/getmenus should retrieve a Json with every item on menu.
You have plenty languages for making a simple rest api
check this related link
Examples of REST APIS

You can store your data (Text/Media) on firebase,It is very easy to start and then enable firebase offline functionality so that it is not required to download data on each launch of application.
Update data on firebase and add valueEventListener in your activity to get that data.

An alternative could be Firebase (by Google).
It's a free and real-time service. It allows you to change the content while the app is running. See "real-time database" and "A/B testing" in Firebase.

i need to change topics in my app every day or every week automaticlly without the user updates the app

I have Christian Android App and there are 5 buttons in my app , I need to update the topics , news and Verses daily or weekly without let the user update the app , is there any way to do that ? I will be grateful if any one help me with tutorials , Please Guide Me THANKS

You can either prepare all possible buttons and choose which to display according to the current timestamp, or you need to build a web API that can provide you with the necessary data and is updatable independent from the app itself.

You must use webservice and SQL DB for this. If you want to add more information for user you just need to update your data base. And in each button tap you should call web api for getting the data.
For web service creation you can use retrofit.
Refer these links
http://www.vogella.com/tutorials/Retrofit/article.html
http://www.journaldev.com/13639/retrofit-android-example-tutorial
https://developer.android.com/training/basics/data-storage/databases.html

Perfect answer by Jacob you can also use cache along with the API call which expires after a specific period. So you don't have to force the user to go online every time he uses your app.

I would do this with notifications, you can have scripts that run weekly to change a topic... and on message receive you can update your topics based on the data coming from the "data-load" this is good because on top of that you can notify them "You have a new topic" or something like that.
There is a lot of resources to set up notifications, and if you are using android studio it is already built in.
https://firebase.google.com/docs/cloud-messaging/

Thanks all for helping me , i already solve my problem through Firebase Realtime Database Because of your posts , thanks again for your help
here is the tutorial https://www.youtube.com/watch?v=QETnC6SEwa0

What is most simple way to send notification of unexpected events to users of Android application?

For example I expect this kind of situation: data in my application lost relevance and so it usless until update. And until update it have to show users some predefined message.
Is here any simple and free solution to this task?
Guess I can use some server to somehow send simple messages... but it sounds way too complicated.
If this is important I use Xamarin.
Update: main difficulty here is fact - my application can't in any way define if it's outdated or not. This may happen in random moment.

Although the requirement is not very clear I assume Update here means app update.
each time user launches app make call to an api on ur server to check if user needs to update app
If that returns true take user to a static view that says app needs update and redirects user to google play to install updates

If you want to avoid using a server, you should try Firebase (https://firebase.google.com/). More specifically, you should use Firebase Remote Config (https://firebase.google.com/features/remote-config/).
Define in a key-value pair of something like minimum_app_version_required in Firebase Remote Config. Every time user opens the your app, compare the values of app version and minimum_app_version_required that you are getting from Firebase console and show a dialog box accordingly. You can also change the value of minimum_app_version_required anytime you want.

Just set some internal flag. That when that situation occurs, you can set the flag to true and just edit whatever layout element you are using such as listView or any other element with your predefined messages saved in strings.xml. You can also build any custom pop up screen, depends how you want to show them. Let me know if you didn't understand or exactly how you want?

Need to implement versioning for this problem. To achieve this, you have to maintain a version number in server, this is the version number you app will have to save and use it to validate with server. If both are not same, then app will get the latest data from the server.

I want to make quiz app that I can update on daily basis

I want to make an android quiz app that I can update on daily basis.Like update daily General knowledge question answers .New section of question set date vice . I am just a beginner in android and need some guidance . So please guide and give some reference that I can use .

You can use Parse.com for such purpose.
Here is link for parse.com for documentation link for parse.com usage example take start from this site link last but not least do follow official android docs link

As you are saying you are new to Android so keep it simple just make the app to fetch the data from server. The other way is to store the data in SQlite and make your app run offline also.
As you have asked I can update on daily basis
So if you want to updates the question then you can do that from your server itself but if you want to update your app then you need to make your app in generalized manner thinking of your future updates, so that you can easily integrate the future functionalities whenever you needed.

for starters, keep the code and data separate, so you can trigger a fetch from a webserver (in XML or whatever format) with the day's quiz data, then parse and display it from your program. and cache it in a text file so you have something to use in case there is no web connection; nobody likes an app that just hangs.

Put some values on internet to access from android

In my app a user can (only) see the values uploaded by admin.
For example. A salesman is using the app will be able to see the latest rate provided by the manger to trade.
Now the question is "where to put these values?"
I have .net webservice experience with android but I guess it wont work in this scenario,will it?
Any suggestion that the returned result be in (preferably) XML format.

It sounds like you already know how to do this. You can download and parse xml within your app. If you alreayd know how to set up the websever, the rest is easy. Limiting who can see what is just a matter of associating specific transactions with an individuals account. Then just have the phone check for updates on that transaction when the app loads (using someting like AsyncTask) or if you want to get more complicated you could push notificatinos using the android cloud service, or even use a REST model. More details are needed for a more specific answer but you can do what you want.

You can do it on your own, and build a webserver with a MySQL/PHP JSON API or you can use parse.com for a smaller project.