Develop Reference

Unable to Initialize SharedPreferences

I have a class A this class does not extend or implement any other classes. I then have an Class B, this class also does not extend or implement any other classes.
My Class B is solely used to manage SharedPreferences :
private static SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(mContext);
Here is the problem method in Class B:
public static void setCurrentUsersEmail(String email){
sharedPreferences.edit().putString("userEmail",email).commit();
}
Now class A is a database manager and needs to store the users email in SharedPreferences for later use. I do this with the following code:`
MySharedPrefs.setCurrentUsersEmail(currentUsersEmail);
However, when i try run the code in Class A i get the error:
java.lang.ExceptionInInitializerError
at com.test.Android.MySharedPrefs.setCurrentUsersEmail(MySharedPrefs.java:0)
I am really confused as to why this happens I couldn't find a solution online after searching either, I use my sharedPreferences class in other activities perfectly fine. Is it an activity problem?
Any help is much appreciated.

You can use singleton for your requirement :
public class MyPrefs {
private static MyPrefs myPrefs;
private SharedPreferences sharedPreferences;
private MyPrefs(Context context){
sharedPreferences=context.getSharedPreferences("MyPREFERENCES", Context.MODE_PRIVATE);
}
public static MyPrefs getInstance(Context context){
if(myPrefs==null)
myPrefs=new MyPrefs(context);
return myPrefs;
}
public void setCurrentUsersEmail(String email){
sharedPreferences.edit().putString("userEmail",email).commit();
}
}
You can put email in this way :
MyPrefs.getInstance(context).setCurrentUsersEmail(currentUsersEmail);
You need to pass context at first time for the reference of sharedPreferences in your Class.
or
From Activity call MyPrefs.getInstance(context) at once
Then you can call without context
MyPrefs.getInstance().setCurrentUsersEmail(currentUsersEmail);
getInstance() method :
public static MyPrefs getInstance(){
if(myPrefs==null) throw new AssertionError("MyPrefs cannot be null");
else
return myPrefs;
}

You could do this , in any activity, dont need to create a new method:
To save:
SharedPreferences.Editor editor = getSharedPreferences(MY_PREFS_NAME, MODE_PRIVATE).edit();
editor.putString("email", "YOURUSEREMAIL#.email");
editor.commit();
To restore:
SharedPreferences prefs = getSharedPreferences(MY_PREFS_NAME, MODE_PRIVATE);
String restoredText = prefs.getString("email", null);
You cant call MyPrefs.aFunctionYouCreated() !!!

Android - Deleting Key Element from SharedPreferences

I'm using the following method to delete a key element on the SharedPreferences of my app. I'm calling it from within a fragment. The problem is that the element is never deleted from SharedPreferences and I get no LogCat output. Is there something wrong with this method? Context perhaps? The deleteFromSharedPreferences is located in a class called Utils and the triggering method is located on a fragment called PagerFragment. Any feedback would be greatly appreciated.
public class PagerFragment extends Fragment {
private void deleteCity() {
deleteFromSharedPref(mCityId, getContext());
}
}
public class Utils {
public static void deleteFromSharedPref(String key, Context context) {
SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(context);
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.remove(key);
editor.apply();
}
}

SharedPreferences produces force close in android program

I'm building an android project that contains SharedPreferences.
My SharedPreferences works fine and I tested it in mutiple activity. but in a class that I defined for global variables, defining that SharedPreferences will cause force close (eclipse didn't show any error in codes).
public class Globals extends Application {
final SharedPreferences s = getSharedPreferences("Prefs", MODE_PRIVATE);
}
What is the problem ?

You should pass the Context and use
SharedPreferences prefs = Context.getSharedPreferences(
"Prefs", Context.MODE_PRIVATE);

Create a constructor and pass a Context variable as a parameter. Any activity that want to use this preference then you have to pass the activity. Here's the code given below:
public class Globals extends Application {
private Context context;
public Globals (Context context) {
this.context = context;
}
SharedPreferences myPref = context.getSharedPreferences("Prefs", Context.MODE_PRIVATE);
}

You can't run getSharedPreferences() in the actual class. Everything you do must be in the Application's onCreate method. If you try to run this in the class, it will fail since it has not been initialized yet. Think of it almost as an activity, since both the activity and the application have a lifecycle.
Try the following:
public class Globals extends Application {
#Override
public void onCreate() {
super.onCreate();
final SharedPreferences s = getSharedPreferences("Prefs", MODE_PRIVATE);
}
}

How access SharedPreferences in another activity ?

I have SharedPreferences in main activity like this :
public class MainActivity extends SherlockFragmentActivity {
public void showUserSettings() {
SharedPreferences sharedPrefs = PreferenceManager
.getDefaultSharedPreferences(getApplicationContext());
Editor editor= sharedPrefs.edit();
editor.putString("userFormat", sharedPrefs.getString("example_list", "2"));
editor.commit();
}
now I wanna get value from SharedPreferences but in bellow class :
public class ReadFormatSharePerf extends Activity {
private DecimalFormat df;
public String finalFormat(String finalFormat) {
SharedPreferences sharedPrefs = PreferenceManager
.getDefaultSharedPreferences(getApplicationContext());
String customFormat = sharedPrefs.getString("userFormat", "#.##");
df = new DecimalFormat(customFormat);
String result = df.format(finalFormat);
return result;
}
I called above activity like this code :
public class Angles {
...
...
ReadFormatSharePerf my= new ReadFormatSharePerf();
result=my.finalFormat(String.valueOf(finalValue));
}
I caught error :
10-16 15:57:24.035: E/AndroidRuntime(10792): java.lang.NullPointerException
atandroid.content.ContextWrapper.getApplicationContext(ContextWrapper.java:101)
how I can do it ?

You should not be instantiating your Activity objects with new. Instead, either make the class not inherit from Activity, or instantiate it via Intent.
The NPE comes from trying to use an Activity as a Context before its onCreate() i.e. in a constructor or a member variable initializer. If you're using the Intent-based instantation, move the code that requires a Context to onCreate() or later in the activity lifecycle. If you make the class not an Activity, pass in a Context reference from caller.

Instead, do:
SharedPreferences sharedPrefs = PreferenceManager
.getDefaultSharedPreferences(this);

This code snippet will help you and Shared Preference KEY values must be same
Saving the values
SharedPreferences preferences = getSharedPreferences("MY_SHARED_PREF",0);
SharedPreferences.Editor editor = preferences.edit();
editor.putInt(String.valueOf(key), value);//store int values, can use string,arrays,etc
editor.commit();
Try to use this
Load the saved values
SharedPreferences getProgramPrefs = this.getSharedPreferences(
"MY_SHARED_PREF", MODE_WORLD_READABLE);
int Index = getProgramPrefs.getInt(String.valueOf(key), -1);

Static SharedPref gives uninitialized value in Broadcast Receiver

I've kept a static shared preference to access the values from multiple activities.
Now, I've set an alarm to go off at a certain time. Now in that Broadcast Receiver, I'm trying to access the shared pref variable.
It has already been initialized in another activity and returns the proper value there.
But in this Broadcast Receiver it doesn't give the actual value. It gives the uninitialized value.
Since it is static shouldn't the value remain same?
Here is the shared preference class.
package com.footballalarm.invincibles;
import android.content.Context;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.util.Log;
public class SessionManagement {
// Shared Preferences
public static SharedPreferences pref;
// Editor for Shared preferences
public static Editor editor;
// Context
Context _context;
// Shared pref mode
int PRIVATE_MODE = 0;
// Shared pref file name
private static final String PREF_NAME = "invincibles_alarm";
// All Shared Preferences Key
public static final String PREF_MATCH = "match";
// Constructor
public SessionManagement(Context context){
this._context = context;
pref = _context.getSharedPreferences(getPrefName(), PRIVATE_MODE);
editor = pref.edit();
editor.commit();
Log.e("Pref Match Value-constructor for pref", getValueMatch());
}
public static void fillValues(String match){
try{// Storing login value as TRUE
editor.putString(PREF_MATCH, match);
// commit changes
editor.commit();
Log.e("Pref Match Value-in fill values", getValueMatch());
}
catch(Exception e)
{Log.e("fillValues", e.toString());}
}
public static String getValueMatch(){
return pref.getString(PREF_MATCH, "Loading Match");
}
public static String getPrefName() {
return PREF_NAME;
}
}
I tried to log the output in other activities and it returns properly.
When I run the app and then close it before the alarm takes place, the program crashes with null-pointer exception since the Broadcast Receiver cannot access the shared pref.
I have tried this solution - SharedPreferences in BroadcastReceiver seems to not update? but I'm only using name in the manifest for the recievers.
This only happens if I close my app in ICS via the minimize menu.

Check this link:
Static variable loses value
Maybe static variables are loosing its value in your case .
static variables can loose value in the following cases:
1) Class is unloaded.
2) JVM shuts down.
3) The process dies.
Instead of using static variables and functions , try using a public class instead.
Hope it helps
EDIT 1:
Example code of using a public class for preferences instead of static methods
public class PreferenceForApp {
Context context;
SharedPreferences prefs;
public PreferenceForApp(Context context) {
this.context = context;
prefs = context.getSharedPreferences(AllConstants.PREFS_NAME, 0);
}
public Boolean getIsDeviceValidated() {
return prefs.getBoolean("Validated", false);
}
public void setIsDeviceValidated(Boolean value) {
SharedPreferences.Editor editor = prefs.edit();
editor.putBoolean("Validated", value);
editor.commit();
}
}
In your code add:
PreferenceForApp myPref = new PreferenceForApp(contxt);
myPref.getIsDeviceValidated();
Useful related links:
Android static object lifecycle
Why are static variables considered evil?
Android : Static variable null on low memory
EDIT 2
TEST when is your static variable loosing value :
You can test this with a few lines of code:
print the uninitialized static in onCreate of your activity -> should print null
initialize the static. print it -> value would be non null
Hit the back button and go to home screen. Note: Home screen is another activity.
Launch your activity again -> the static variable will be non-null
Kill your application process from DDMS(stop button in the devices window).
Restart your activity -> the static will have null value.
I referred to this link Android static object lifecycle