Develop Reference

Does SharedPreferences name need to be unique?

Probably a dumb question, but I"m using a SharedPreference with a few different names "MyPrefs1", "MyPrefs2" etc.
I'm assuming this is restricted to my app. i.e. if some other app tries to use the same name, it won't overwrite my values
I pretty much believe my understanding is correct, but the name "SharedPreferences" seem to indicate that it can be shared between apps? (is it for Sharing between activities?)

That's correct, the SharedPreferences are stored in your app's private folder (to be exact, in /data/data/your package name/shared_prefs).
You can give them whatever name you want.

SharedPreferences represent the preferences which can be shared between different components of your application. The SharedPreferences you create in your application is never exposed with other applications.
Whether you use PreferenceManager.getDefaultSharedPreferences() or Context.getSharedPreferences("file_name", Context.MODE_PRIVATE); both are particular to your application only.
Note - SharedPreferences or Preferences is not exposed to other applications.

Although you assumption is right that the SharedPreferences are not shared between apps and thus names cannot clash, it's a good practice (besides of put a specific name to your shared preferences file) to add the package of your application as a prefix. This is useful if you have different flavours and you don't want to overwrite your preferences among them, especially when you're testing an app and don't want to screw up the original values of the shared preferences files.

What is the best way to store string? SharedPreferences Set Collection or Files?

I have to store some data (string) in my Android app and I'm a dilemma. What is better solution ? Use Set Collection and keep it at SharedPreferences or I should save data to File and when I need it I have to read data from file and put it for example on ArrayList.

Depends on the quantity & complexity of the data. There is no straight answer to your question.
General approach: If the data are not too sensitive, small in quantity and more frequently used then you should go with SharedPreferences.
If your data is quite large lets say few hundred KBs of String then you should go with File.

SharedPreferences ultimately stores data into a file. The advantage of using SharedPreferences is that, the data is stored as a key value pair and can be retrieved easily using a key.

It depends on what you want to store.
Use SharedPreferences when you want store simple, prmitive data. Keep in mind that SharedPreferences will be available only for your app, so anothers apps cannot get data from it.
Use File when you have more complex data. You have to take care about how file is available to others. If you put it in sdcard root directory for example it will be available for everyone. If you put it in app package it will behave like SharedPreferences.

How the SharedPreferences works and is it safe

I'm going to use the SharedPreferences Keys to store my app informations so when I open the app again after onDestroy the information will still the same.
I'm just wondering is it safe to use SharePreferences ? I mean is there a way to hack or get the KEYS from the SharePreferences ?
and does all Android Platforms have the SharePreferences ?
thanks .

sharedPreferences arent safe..
sharedPreferences should just store config/setting-data not encrypted..
if u want to store critical data - you have to write it encrypted in a dataBase/sharedPrefs
btw .. http://android-developers.blogspot.de/2013/02/using-cryptography-to-store-credentials.html

You shouldn't store any unencrypted valuable information(passwords, private user information etc.) in SharedPreferences. SharedPreferences are just plain XML files in app directory on internal storage.
If you need to store smth private - you definitely need to encrypt it first.

What is the purpose of SharedPreferences in Android ?

What is the purpose of SharedPreferences in Android?
Why it is used ?
Where it want to be use?

Shared preferences is used to save any primitive data: booleans, floats, ints, longs, and strings. This data will persist across user sessions (even if your application is killed).
for more visit here
reference earlier answered

You can read the developer android site about SharedPreference to save light data till your application exists into user's device. It will remain saved even after existing your application.
Storage in android with SharedPreference
SharedPreference in android
Hope it will help you..!!!

SharedPreferences is used to permanently store preferences in key:value pair
SharedPreferences is accessible by all the Activity(ies) of an app. Other app cannot directly access the content of shared_prefs
App stores its data/preferences in the SharedPreferences.
E.g. Say in a game u can store ur score, game level, user name, no of kill, etc in the preferences; so that it is accessible all throughout the game; yet by that particular game only.
Game "Gold Miner 2" does it. It is only one example.
Svox tts save ANDROID_ID in preferences file;
You need to keep in mind that if u delete the app, all SharedPreferences will be deleted (/data/data//shared_prefs);

Difference between shared preference and sqlite

I know this topic has been discussed before on Stack Overflow. But there are still some things that are not clear when I read previous posts about it. So here they are:
I know that we use shared preference for small datasets and sqlite for large data manipulation, so if we just want to save a username and password should we use shared preferences?
Won't shared preferences be lost when user uninstalls the app? For example I download an app called abc and save my username and password. Then I uninstall this app from one phone and try to access it from other phone using the same username and password. Will this be saved using shared preferences or the data be lost?
What are the main reason we use one over the other beside large and small datasets?

You can think of the difference between shared preferences and an SQLite database in terms of data size but that isn't entirely accurate. A better way to think of it is in terms of the structure of the data you want to store.
Shared preferences can only store key-value pairings whilst an SQLite database is much more flexible. So shared preferences are particularly useful for storing user preferences, e.g. should the app display notifications etc. Whilst an SQLite database is useful for just about anything.
Both data sources are local but something you should be aware of is the ability to backup your application data to cloud storage that is linked to the user's Google account. This makes it much easier for your users to change devices and for their applications to easily transfer to the new device. For more info take a look here.

In the situation you described about you will lose the user name and password in both situations. The data is stored on the phone, when you uninstall the application, the data that some with it will also be lost. The user will have to re-enter this information.
You can save the user name and pass in either the shared Preferences or a DB, that is personal preference. Just make sure you lock either down, i.e. don't share the DB or Shared Preferences that you keep this information in.
As for the difference... shared Preferences should hold well... shared Preferences... here is an example:
If I create an option to change the background color, I will store all available options in a DB that can be loaded into a adapter view for the user to choose from. But I will store the color that they have selected in the Shared Preferences. This way when the application load I can get the Shared Preference value of the background color that should be used.

SharedPreferences is used for just that, storing user preferences shared application-wide. You can use it, for example, to store a user's username, or perhaps some options he or she has configured in your app in which you want to remember.
SQLite is a relational database. It's used to store your application's data, not preferences or configuration information.
Both are stored locally on the device.

1.SharedPreferences stores only Boolean, int, float, long, String five kinds of simple data types, such as can not be conditional query. So, whether SharedPreferences data storage operation is how simple it can only be a supplement of storage, but can not completely replace other data such as the SQLite database is stored.
2.SharedPreferences based on the XML file to store key-value key used to store configuration information(mainly user preference for your application).
3.Sharedprefrece just like cookies in web which store some basic information at client side.

both store their data locally, so uninstalling the app will delete both. other than that, SharedPreferences is easier to program, and you're right about the data amounts.

In general, shared preferences should be used if you want to allow your user to directly manipulate certain data fields. Shared preferences are basically user preferences; if you would like the user to reconfigure the app to behave in different ways, you should expose that functionality as a shared preference. On the other hand, the SQLite database should be used if you want to limit the visibility of the data to just the application, if you want a stronger guarantee that the data be persistent, and if you want the application to behave independently of what is stored in the database. Of course, you can use both in one application.
Shared preferences and the database are part of local data that the application stores. If you uninstall the application, both of the data stores will be removed.