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Android Static Variables and Shared Preferences

I am writing an android app and I retrieve a balance for the user from a webservice and the user is able to log in and out of my app.
When the app starts I check the shared preferences to see if the user is logged in or out. On correct log in I update the shared pref boolean to true and set it to false when the user logs out.
I need to know the balance in several fragments and I need to remember it when I am navigating thru the fragments in my app. When I return to the "My Account" fragment balance value is lost and I have to call my web service again to check it.
It the best way to use a string shared pref and update it any time the app starts or when there is a change in the balance. Or am I better to use a static variable in my main activity that can be referenced when the user navigates to the My Account fragment.
Is it possible to overuse shared preferences?

A simple and elegant solution is to use a very simple library TinyDB in android, which is nothing but an abstraction over the Shared Preferences.
You can initialise it in your activity's onCreate() method like this:
TinyDB tinydb = new TinyDB(this);
In fragment, just replace this with getActivity.
And then use it like this:
tinydb.putString("userName", "john");
String currentUser = tinydb.getString("userName");
Hope it helps.

For a single value such as balance or username you should definitely use SharedPrefereneces and OnSharedPreferenceChangeListener.
For structured data such as balance operations you should definitely use a database:
SQLite
Realm (noSQL)
StorIO (SQLite wrapper)
or some ORM.

There is 3 way to store you login details .
Using Shared Preference
Store Data in a File
Using Sqlite.
This tutorial will give you the ideas for storing login details.

You should store data in SharedPreferences rather than global variables because when app crashes, the data updated in static global variables at different times is lost and the default data in it remains.

How to save number of times a user has tapped on a view

I am designing a simple application that will count how many times a user has tapped on a imageView. My question is what would be the best way of saving and reading this file. Any suggestions? I am thinking something like using Parse.com's local database. I have tried it, but I could not get it working the way I wanted. I am still a beginner, so please not so fancy suggestions.

Try to save data in SharedPreference. SharedPreference works like database for application on device that will be stored until any one has unistall app from device.
To create sharedPrefernce-
SharedPreferences prefs = this.getSharedPreferences(
"com.example.app", Context.MODE_PRIVATE);
To store data -
prefs.edit().putInt("key", int_value).apply();
To retrieve data-
// use a default value
int l = prefs.getLong("key", default_value);

Simplest options is always thebest option, go with shared preferences
Here is simple tutorial from google http://developer.android.com/training/basics/data-storage/shared-preferences.html
It will store your data in application local file. Take a note of that there are different shared preferences in example getPreferences() will return file specific for activity you used this method. While getSharedPreferences() will return application global file.

Saving Shared Prefrences in Multiple instances

I would like to be able to save my users session or sharedPrefrences in a way that if the user kills the application and you start it it would look like this.
Button one = Start Activity with Blank Preferences
Button Two = List of Saved Sessions of Preferences and once clicked all put into the Starting activity.
Is this possible and if so how would I go about doing that?
Thank you!

Yes you can do that and it is good to use sharedPreferences if you just have to store some session variables. But if it is more, then go for database.
Do clear sharedPrefences in your application you need to do this:
SharedPreferences settings = PreferenceManager.getDefaultSharedPreferences(activity);
Editor editor = settings.edit();
editor.clear();
editor.commit();
For reading the preferences, you can keep a sharedPreference with the count for the seesions. While saveing the prefences, always save with the strings session1, session2, session3 etc. So, while accessing them based on count, prepare a loop and form the string and access all the session variables and show them.
The reason why I didnt suggest you to do getAll() for sharedPreference is that, you may save few other things in sharedPreference. So by forming strings yourself, while reading you can just get the sessions and not other data saved in sharedPreference.
I hope you understand what I meant

Is this possible
I would say yes, depending on exactly what you mean.
if so how would I go about doing that?
SharedPreferences has a couple different functions to do something like this, depending on exactly what you want. You can get a Map of all preferences that are stored after clicking Button2 with getAll() or a set of preferences with a certain String such as "userName" or something similar with getStringSet(). Play around with the functions it offers and see if it gives you what you are looking for.
Also take not of the warnings of these functions
Note that you must not modify the set instance returned by this call. The consistency of the stored data is not guaranteed if you do, nor is your ability to modify the instance at all.

Initializing Preferences

Android Guide recommends defining preferences in XML files, And from there, these can be loaded in PreferenceActivity/PreferenceFragment etc for viewing and editing by user. But in real scenario, User Interacts with other activities first, then (maybe) with Preferences UI.
What if the starter activity needs some of these preferences ? They'll be not loaded yet, because preferences resources has not been inflated yet. Is there a way to pre-access preferences in XML files ?

Yes. When you first request the preference you can provide it with a default value. E.g. if you are loading a preference of type Int, then you can do so in the following manner from an activity:
SharedPreferences defaultSettings = PreferenceManager.getDefaultSharedPreferences(this);
int preferenceValue = defaultSettings.getInt("PreferenceName", 7);
This would load your preferenceValue to be 7 (without this preference ever being initialized yet). This is assuming that in your XML preference file, you have a preference of key "PreferenceName". If you plan on editing this preference in the activity before the Preference activity has been ran, be sure you commit your changes with a SharedPreferenceEditor:
// ... change to preferenceValue occurs prior to this code
SharedPreferences.Editor defaultEditor = defaultSettings.edit();
defaultEditor.putInt("PreferenceName", preferenceValue);
defaultEditor.commit();
We probably want to avoid "PreferenceName" in a hardcoded matter though, and instead use it as a string in the strings.xml file. This way it can be grabbed both from the initial code when the preference has not been saved yet and from the Preference XML file as well. This means that our above code would substitute the string "PreferenceName" with something like the following:
getResources().getString(R.string.pref_name)
And in your Preference XML file you may would reference the key in the following way:
android:key="#string/pref_name"
android:defaultValue="7"
This should cover "pre-loading" the preference as well as trying to keep most of the application settings within one place. There may indeed be overlap in terms of whether or not the XML preference was created/loaded before the initial Activity occurred, but I haven't tested that out yet.
EDIT: It turns out instead of using the above code, you can directly load the XML file (with its default preference) by the following method:
PreferenceManager.setDefaultValues(this, R.xml.preference, false);
More information about this method can be found in the documentation for the PreferenceManager: http://developer.android.com/reference/android/preference/PreferenceManager.html

If you look at SharedPreference API, you will see this
getString(String key, String defValue)
So, you can actually in fact define a default value if it's not already existed.
Source: http://developer.android.com/reference/android/content/SharedPreferences.html
You can also predefine default value in XML using
android:defaultValue="SOMETHING"

How to attach a Preference to a particular SharedPreferences?

I am working on implementing the preferences for our application. I know how to display preferences UI and how to read/write values using SharedPreferences. In our app, I need to handle two sets of preferences and I would like to ask about this issue, one comment in the Android documents in particular.
The documentation for Preference.getSharedPreferences() has the following comment under the Return values section:
Returns The SharedPreferences where this Preference reads its value(s), or null if it isn't attached to a Preference hierarchy.
I would like to ask how it is possible to attach a SharedPreferences to a particular Preference, be it EditTextPreference or others. In other words, how does the persistence code in a Preference know that it should store the user input in one particular SharedPreferences object and not the other?
To explain my question further with an example, suppose I have the following:
SharedPreferences prefs1 = getSharedPreferences(file1, mode);
SharedPreferences prefs2 = getSharedPreferences(file2, mode);
My question is what API I should use so that prefs1 is used by the Preference objects' persistence code and not prefs2.
The target is Nexus One, running 2.3.4.
Maybe the answer is obvious but I could not find it after reading the documentation and searching the web. Thank you in advance for your help.

In other words, how does the persistence code in a Preference know that it should store the user input in one particular SharedPreferences object and not the other?
Preference uses PreferenceManager's getSharedPreferences(), which eventually routes to getDefaultSharedPreferences().
You are welcome to create your own Preference subclasses that change this behavior, but since the preference screen system may not be designed to handle multiple SharedPreference objects, there's a chance that your preference changes might not get persisted.
IOW, I encourage you to reconsider:
In our app, I need to handle two sets of preferences