Develop Reference

Declaring a android Global Variable that changes time to time

I am creating a location tracking application where I want the email-id of the logged in person as a global variable. As the email will keep changing depending on who logs in, i have a little confusion on how to go about with.
Thanku :)

Instead of creating Global variables please, Shared preferences and save them. Now, you can access them across the app or even after when user come back to app after closing App. Just as following :
SharedPreferences sharedPref = getActivity().getPreferences(Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPref.edit();
editor.putString("email", test#gmail.com);
editor.commit();
//to read shared prefere
SharedPreferences sharedPref = getActivity().getPreferences(Context.MODE_PRIVATE);
String defaultValue = "test#gmail.com"; //this is default email, so if you don't have values in preferences then it will be returned
String email= sharedPref.getString("email", defaultValue );
For details, Please follow Tutorial at: Official doc : SharedPreferences - Saving Key-Value Sets

As Kunu recomended, SharedPreferences are for these cases.
public static String PREFS_NAME = "loginDetails";
public static String LOGGED_EMAIL = "Email";
To edit your email:
public static void editEmail(String email)
{
Context context = getAppContext();
SharedPreferences.Editor editor = context.getSharedPreferences(PREFS_NAME, MODE_PRIVATE).edit();
editor.putString(LOGGED_EMAIL , email);
editor.apply();
}
For more details about SharedPreferences check this answer.

sharedPreferences in Fragment

I know this has been asked before, but i can't seem to figure it out
i am trying to get my preferences by this:
SharedPreferences preferences = this.getActivity().getSharedPreferences("storedName", Context.MODE_PRIVATE);
String loginemail = preferences.getString("storedName", "");
but this doesn't seem to work, i have multiple sharedPreferences which i need to get in my fragment what is the correct way to do it?
As getDefaulSharedPreferences(this) doesn't work.
i store my prefs like so:
savePreferences("shareUniqePass", uniqePassIds.getText().toString());
savePreferences("storedName", inputEmail.getText().toString());
savePreferences("Storedpass", inputPassword.getText().toString());
private void savePreferences(String key, boolean value){
SharedPreferences sharedPreferences = PreferenceManager
.getDefaultSharedPreferences(this);
Editor checkbox = sharedPreferences.edit();
checkbox.putBoolean(key, value);
checkbox.commit();
}
private void savePreferences(String key, String value){
SharedPreferences sharedPreferences = PreferenceManager
.getDefaultSharedPreferences(this);
Editor names = sharedPreferences.edit();
names.putString(key, value);
names.commit();
}

Instead of getting it from getSharedPreferences use the getDefaultSharedPreferences.
As getDefaulSharedPreferences(this) doesn't work.
You used getDefaultSharedPreferences for saving the data and therefore you must use getDefaultSharedPreferences to get the data that was saved.
this mean the instance of your fragment instead use the getActivity() to get the instance of context from your activity.
sample:
String loginemail = PreferenceManager.getDefaultSharedPreferences(getActivity()).getString(PREF_USER_NAME, "");;

You need to make sure that your saving and loading the data from the same shared preferences. If you're only accessing it from the one activity / fragment, you should use getDefaulSharedPreferences(this).
If, however, you're going to use it from several different activities / fragments, you should use:
private void savePreferences(String key, boolean value){
SharedPreferences prefs = getActivity().getSharedPreferences("storedName", Context.MODE_PRIVATE);
Editor checkbox = sharedPreferences.edit();
checkbox.putBoolean(key, value);
checkbox.commit();
}

How do I set up a global variable to share among views in Android?

In one of my views the user makes a selection. I want to store that selection in a variable I can use across all views so it can be used for further database queries such as "bookId".
How can I make "bookId" a global variable that is set on one view and can be accessed across the other views when needed?
----- Edit: What I'm attempting to do based on comments and answers -----
On my main activity where the SharedPreference is stored I have this before the onCreate:
public static final String PREFS_NAME = "myPrefs";
SharedPreferences settings;
Integer bookId;
In my onCreate I've done this:
settings = getSharedPreferences(PREFS_NAME, 0);
bookId = settings.getInt("bookId", 0);
After the button press I'm storing a custom attribute and attempting to set bookId in the SharedPreference:
SharedPreferences.Editor editor = settings.edit();
editor.putInt("bookId",bookKey);
editor.commit();
In another view I'm attempting to get the bookId from the SharedPreference and, for testing purposes, I'm trying to set the stored value to a textView just to make sure it stored and carried over correctly.
Before the onCreate on the second view:
public static final String PREFS_NAME = "myPrefs";
SharedPreferences settings;
Inside the onCreate:
settings = getSharedPreferences(PREFS_NAME, 0);
Integer bookId = settings.getInt("bookId", (Integer) null);
tempBookTextView = (TextView) findViewById(R.id.tempBookTextView);
tempBookTextView.setText(bookId);
I have a two questions, how does this look so far? Any ideas why the app crashes when I use
Integer bookId = settings.getInt("bookId", (Integer) null);

Instead of using global variable to access variable value through out the app try using SharedPreferences.
sample activity:
public class Book extends Activity {
public static final String PREFS_NAME = "MyPrefsFile";
String mBookId = null;
#Override
protected void onCreate(Bundle state){
super.onCreate(state);
. . .
// Restore preferences
SharedPreferences settings = getSharedPreferences(PREFS_NAME, 0);
mBookId = settings.getString("book_id", null);
// use book_id;
}
#Override
protected void onStop(){
super.onStop();
// We need an Editor object to make preference changes.
// All objects are from android.context.Context
SharedPreferences settings = getSharedPreferences(PREFS_NAME, 0);
SharedPreferences.Editor editor = settings.edit();
editor.putString("book_id", mBookId);
// Commit the edits!
editor.commit();
}
}
Preferences are typically created private and can be accessed via all over the application components. Sharing data with other application with world readable or writable preference file is rarely used, as the external component would need to know the exact filename and location of the file.

To kill the spirit of encapsulation,
public class Globals {
public static int x;
public static int y;
}
and later
if (Globals.x == 0) { ... }
But please don't do exactly that, any class can contain static variables, find a class responsible for the value you want to store.
OTOH, android processes may be restarted when you don't expect it, in which case all the variables will be reset. So it's better to use shared preferences and if they don't work as expected (which I have seen in at least one release of Android), store the instance of shared preferences in a static variable.

You can use Shared Preferences
Saved at once !
SharedPreferences.Editor editor = PreferenceManager.getDefaultSharedPreferences(ProjectAct.this).edit();
editor.putInteger(StaticVariable.BOOKID, "1");
p.get("contract_no"));
editor.commit();
Then call from anywhere like that
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);
int book_id = prefs.getInteger(StaticVariable.BOOKID,null);
See more at How to use SharedPreferences in Android to store, fetch and edit values

SharedPreferences

I'm creating a SharedPreferences and it's working only if I start Activity like this:
myIntent.putExtra("prefName", MYPREFS);
startActivity(myIntent);
But my SharedPreferences is not working after I save it and hit back a few times, to go at menu page and go to the page where I want to get my preferences.
Anyone can help me with that?
Code below:
This is where I save my preferences:
String MYPREFS = "MyPref";
SharedPreferences mySharedPreferences;
SharedPreferences.Editor myEditor;
Inside onCreate:
mySharedPreferences = getSharedPreferences(MYPREFS,0);
myEditor = mySharedPreferences.edit();
Inside button onClickListener:
myEditor.putString("address", AddressET.getText().toString());
myEditor.putString("contact", ContactET.getText().toString());
myEditor.commit();
Intent myIntent = new Intent(myContext, nok_individual_particular.class);
myIntent.putExtra("prefName", MYPREFS);
startActivity(myIntent);
This is the activity I pass to:
SharedPreferences mySharedPreferences;
Inside onCreate:
Intent myReceivingIntent = getIntent();
String myPREFName = myReceivingIntent.getStringExtra("prefName");
mySharedPreferences = getSharedPreferences(myPREFName, 0);
applySavedPreferences();
In the applySavedPreferences method:
String addressValue = mySharedPreferences.getString("address", "Jack Smith");
String contactValue = mySharedPreferences.getString("contact", "Jack Smith");
addressTV.setText(addressValue);
contactTV.setText(contactValue);

SharedPreferences: This is how it works
To save your data:
SharedPreferences sPrefs = getSharedPreferences("prefsName", 0);
SharedPreferences.Editor editor = sPrefs.edit();
editor.putString("valueName", "value");
editor.commit();
To retrieve your data:
SharedPreferences sPrefs = getSharedPreferences("prefsName", 0);
String strMyData = sPrefs.getString("valueName", "default value");
The example above is how to set a string and retrieve it.

You are not using SharedPreferences. In your example, you are passing an extra to an activity, but this only makes available the value to the new activity, it doesn't save the value to SharedPreferences.
To use SharedPreferences, you have to do the following:
Save
PreferenceManager.getDefaultSharedPreferences(this).edit().putString("prefName", "String to save").commit();
Get
String value = PreferenceManager.getDefaultSharedPreferences(this).getString("prefName"), "default value");

After mySharedPreferences.edit();
mySharedPreferences.commit();
should be your last line. This enables u to save and close the SharedPreferences file you have edited.
Well, you don't need to pass the sharedprefs in an intent and all. It will be available throughout your application in all activities.
Just call SharedPreferences my_prefs= getSharedPreferences("Pref_name", 0); and then u have a reference to that SharedPreferences file and then u can retrieve values from it.

I prefer using SharedPreferences to save my data and use it throughout my classes , plus they will be saved to the device , making them available even after the app is killed ... Here is an example for ya !
//Some String that I should remember, I am just using the package name for now
String app = this.getPackageName();/*This is going to be used more like a file to save my stuff to*/
//Setting our sharedpreferences
SharedPreferences sha = sha = getApplicationContext().getSharedPreferences(app, SherlockActivity.MODE_PRIVATE);
String myString = "This is the String that you want to save so you can use among your classes"
//Now we call in an editor for that SharedPreferences so we can write and delete stuff from it .
Editor edit = sha.edit();
//Now we insert our String.
edit.putString("Something_you_can_remember" , myString);//You will need the "Something_you_can_remember" a few lines ahead , so remember it !
edit.apply(); //Or we can use edit.commit() , but I prefer apply()
//Now our String is saved ! So lets read it !
String whatever = sha.getString("Something_you_can_remember" , "The String incase myString didn't even exist , saves you from a NullPointerException");
//Here we go ! Now we have our String saved and can be readable among the classes !
//Also , if you wanted to delete that String or whatever you "put" in there , you can call
edit.remove("Something_you_can_remember"); //or edit.clear() to remove all the values stored !
Hope this helps !

Save
SharedPreferences sp = getSharedPreferences("key", 0);
SharedPreferences.Editor sedt = sp.edit();
sedt.putString("valueName", "String to save");
sedt.commit();
Get
SharedPreferences sp = getSharedPreferences("key", 0);
String valueName = sp.getString("valueName","");

You do not need to pass SharedPrefences through intents, as SharedPreferences are available to the whole application and any activity has access to it.
You can refer to below example:
Either create SharedPreferences by giving them your choice of name:
SharedPreferences pref = getSharedPreferences("MyPref", MODE_PRIVATE);
OR use default SharedPreferences:
SharedPreferences sharedPrefs = PreferenceManager.getDefaultSharedPreferences(this);
Use your preference file anywhere in your code by getting them through any of the above methods. No need to pass to different activities.
Once you call any of the above method, if the preference file of that name does not exist for your application, android will create one for you.

Trouble using sharedPreferences between two activities

I am trying to save a date in one activity and then have that date put in a textView in another activity. I am not sure about how to get the two activities to communicate with each other.
In file called report.java I have this method that gets the date and save it in sharedPrefernces.
private void updateLabel() {
date.setText(fmtDate.format(dateAndTime.getTime()));
SharedPreferences preferences = getPreferences(MODE_PRIVATE);
SharedPreferences.Editor editor = preferences.edit();
editor.putString("date", date.getText().toString()); // value to store
editor.commit();
}
I am trying to figure out how to get my file called inspection use this to populate a textView
The problem I think I am having is with getting the correct name for the report file.
public static final String PREF_FILE_NAME = "report";
SharedPreferences preferences = getSharedPreferences(PREF_FILE_NAME, MODE_PRIVATE);
then I have this code on a method called onResume()
#Override
public void onResume() {
super.onResume();
SharedPreferences preferences = getPreferences(MODE_PRIVATE);
String strDate=preferences.getString("date", date.getText().toString());
date.setText(strDate);
}

You are saving the value to two seperate preference files.
SharedPreferences preferences = getPreferences(MODE_PRIVATE);
SharedPreferences preferences = getSharedPreferences(PREF_FILE_NAME, MODE_PRIVATE);
Use only one.

Why not use the default preference file that is accessible by all classes/activities of your app?
SharedPreferences preference = PreferenceManager.getDefaultSharedPreferences(yourContext);
preferences.edit().putString(YOURKEY, yourStrValue);
This way you are not creating extra preference files in your app that you have to remember which values are stored in which files. Definately makes life easier.