Develop Reference

How to use Shared Preferences?

I am new to android..and I'm developing an application using Json. I want to pass a string value from my main activity to another class without starting the activity class. I heard there is some way using shared preferences. I just tried.. but didn't worked..i got null point exception.. here is my code...
confirm = check.AuthenticateUser(name, passwd);
SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
SharedPreferences.Editor editor = preferences.edit();
editor.putString("Name",confirm);
editor.commit();
here is the place i want to send the value of "confirm" (string variable)
and below code shows where i want to get that preference..actually that class named "ShortList".
here is the code where i trying to get the value
public class ShortList extends Activity {
//ArrayList<HashMap<String, String>> arl;
SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);
String cargivr = preferences.getString("Name","");
please some one help me..

public static String CREDENTIALS_FILENAME = "com.myapp.credentials";
public static String PIN = "pin";
public static void writeCredentials(Context c,String pin) {
SharedPreferences credentialsPref = c.getSharedPreferences(CREDENTIALS_FILENAME, 0);
SharedPreferences.Editor editor = credentialsPref.edit();
editor.putString(PIN, pin);
editor.commit();
}
public static String readCredentials(Context c,String pin) {
SharedPreferences credentialsPref = c.getSharedPreferences(CREDENTIALS_FILENAME, 0);
SharedPreferences.Editor editor = credentialsPref.edit();
return credentialsPref.getString(PIN, "default value");
}

MainActivity.java
SharedPreferences pref = getApplicationContext().getSharedPreferences("New",Context.MODE_PRIVATE);
Editor edit = pref.edit();
edit.putString("SomeKey", "SomeValue");
edit.commit();
SecondActivity.java
SharedPreferences prefs = getApplicationContext().getSharedPreferences("New",Context.MODE_PRIVATE);
String value = prefs.getString("SomeKey","DefaultValue");
Also make sure that you have added the second activity details in your android manifest file -
<activity
android:name="com.example.projectName.SecondActivity"
android:parentActivityName="com.example.sharedpref.MainActivity">
</activity>

public class ShortList extends Activity {
//ArrayList<HashMap<String, String>> arl;
SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);
String cargivr = preferences.getString("Name","");
Here it seems you're initializing member variables.
You cannot use an Activity as a Context until onCreate() in the activity lifecycle. Member variable initialization is too early and will usually lead to NPE in getBaseContext().
Move the initialization of preferences and cargivr to onCreate() or later.

SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(ShortList.this);
String cargivr = preferences.getString("Name","");

Android SharedPreferences update does not work

I know, this issue has been dealt with in many threads, but I cannot figure out this one.
So I set a shared preference like this:
SharedPreferences prefs = MainActivity.this.getPreferences(MODE_PRIVATE);
SharedPreferences.Editor editor = prefs.edit();
editor.putStringSet(spinnerName, myValueSet );
editor.apply();
I read the preferences like this:
SharedPreferences prefs = MainActivity.this.getPreferences(MODE_PRIVATE);
Set<String> spinnerValuesSet = null;
spinnerValuesSet = prefs.getStringSet(spinnerName,null );
Everything works, except for my changes are visible while this activity runs i.e. - I display the values from the SharedPreferences, allow the user to delete or add and then update the ListView. This works, but after I restart the application, I get the initial values.
This for example is my method to delete one value from the list, update the values in SharedPreferences and update the ListView
Button btn = (Button) findViewById(R.id.button1);
btn.setOnClickListener(new OnClickListener(){
#Override
public void onClick(View arg0) {
SharedPreferences prefs = MainActivity.this.getPreferences(MODE_PRIVATE);
Set<String> spinnerValuesSet = prefs.getStringSet(spinnerName,null );
for (String s : spinnerValuesSet)
{
if(s == currentSelectedItemString)
{
spinnerValuesSet.remove(s);
SharedPreferences.Editor editor = prefs.edit();
editor.putStringSet(spinnerName, spinnerValuesSet );
editor.apply();
break;
}
}
updateListValues();
}
});
And this is the method that updates the ListView:
private void updateListValues()
{
SharedPreferences prefs = MainActivity.this.getPreferences(MODE_PRIVATE);
Set<String> spinnerValuesSet = prefs.getStringSet(spinnerName,null );
if(spinnerValuesSet.size() > 0)
{
names = new ArrayList<String>();
names.clear();
int k=0;
for (String s : spinnerValuesSet) {
names.add(k, s);
k++;
}
namesAA = new ArrayAdapter<String> ( this, android.R.layout.simple_list_item_activated_1, names );
myList.setAdapter(namesAA);
}
}
Any help is much appreciated.

The Objects returned by the various get methods of SharedPreferences should be treated as immutable. See SharedPreferences Class Overview for reference.
You must call remove(String) through the SharedPreferences.Editor returned by SharedPreferences.edit() rather than directly on the Set returned by SharedPreferences.getStringSet(String, Set<String>).
You will need to construct a new Set of Strings containing the updated content each time since you have to remove the Set entry from SharedPreferences when you want to update its content.

Problem happens because the Set returned by SharedPreference is immutable. https://code.google.com/p/android/issues/detail?id=27801
I solved this by created a new instance of Set and storing in all the values returned from SharedPreferences.
//Set<String> address_ids = ids from Shared Preferences...
//Create a new instance and store everything there.
Set<String> all_address_ids = new HashSet<String>();
all_address_ids.addAll(address_ids);
Now use the new instance to push the update back to SharedPreferences

I may be wrong but I think the way you are retrieving the Shared Preferences is the problem. Try using
SharedPreferences prefs = getSharedPreferences("appPreferenceKey", Context.Mode_Private);

Use editor.commit(); instead of editor.apply();
Example Code:
SharedPreferences prefs = MainActivity.this.getPreferences(MODE_PRIVATE);
SharedPreferences.Editor editor = prefs.edit();
editor.putStringSet(spinnerName, myValueSet );
editor.commit();
I hope this helps.

Depending on the OS Build you may have to save values in a different way.
boolean apply = Build.VERSION.SDK_INT >= Build.VERSION_CODES.GINGERBREAD;
public static void saveValue(SharedPreferences.Editor editor)
{
if(apply) {
editor.apply();
} else {
editor.commit();
}
}

Android Shared Preferences Saving Highscore and Unlocks

I have 27 characters that I want a player to unlock by beating scores, e.g. if his score is greater than 200 he unlocks character #1. I have a hard time trying to do that.
I have a class for characters that contains its number, the score required to unlock it, and a boolean to check if he is unlocked. But when it comes down to saving, I can't do that.
The main game loop is in file GameScreen. It has a value points counting the score.
When GameState changes to PlayerDead I want to check if any new character has been unlocked, and whether the high score has been beaten to save points.
Please help, I'm struggling with it for over a week and I can't find a good tutorial for SharedPrefs because all of them apply to GUI based activity that saves the name and surname you entered.

if you need sharedPrefs I can help you.
I can give some some example code.
or you can send your code and error if you get one, we update it.
but sharedPrefs is a good idea for that ? if user goes to application settings and clears data of your app, all data will be lost.
why dont you try create a sqlite databade, save it into assets directory and use it?

It's actually pretty simple, you use SharedPreferences to store key-value pairs. You can either call
SharedPreferences mPrefs = PreferenceManager.getDefaultSharedPreferences(this);
From the GameScreen and then define a constant:
public static final String KEY_SCORE = "score";
To use as the key for the saving.
In order to actually save, you need an Editor:
SharedPreferences.Editor mEditor = mPrefs.edit();
//save data now, mPlayerScore is the score you keep track of
//if it's another type call putString(), etc
mEditor.putInt(KEY_SCORE, mPlayerScore);
//if that is the only thing you want for noe
//close and commit
mEditor.commit();
And in order to retrieve the saved score, during your onCreate() you can do:
public void getUserProgress() {
SharedPreferences mPrefs = PreferenceManager.getDefaultSharedPreferences(this);
//no need for an editor when retrieving
mPlayerScore = mPrefs.getInt(KEY_SCORE, 0);
//second value passed was the default score
//if no score was found
}
In order to check for new character s being unlocked, you can call the following code after every game:
private void checkForUserUnlocks() {
if (mPlayerScore >= MyUnlockableCharacter.SCORE_NEEDED_TO_UNLOCK)
MyUnlockableCharacter.isUnlocked = true;
//and same for other unlockabld characters
}
There are other ways to access SharedPreferences, let me know if you need more info.

Use the below code to store and retrieve Score from SharedPreference.
public static void saveScore(Context context, int score){
SharedPreferences sharedPreferences = context.getSharedPreferences("YOUR_PACKAGE_NAME", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.putInt("SCORE", value);
editor.commit();
}
public static int loadScore(Context context){
SharedPreferences sharedPreferences = context.getSharedPreferences("YOUR_PACKAGE_NAME", Context.MODE_PRIVATE);
int score = sharedPreferences.getInt("SCORE", 0);
return score;
}

Read Sample;
public int Read() {
SharedPreferences mSharedPrefs = getSharedPreferences("FileName",
MODE_PRIVATE);
SharedPreferences.Editor mPrefsEditor = mSharedPrefs.edit();
int mCounter = mSharedPrefs.getInt("Counter", 0);
return mCounter;
}
Write Sample;
public void Write() {
SharedPreferences mSharedPrefs = getSharedPreferences("FileName",
MODE_PRIVATE);
SharedPreferences.Editor mPrefsEditor = mSharedPrefs.edit();
mPrefsEditor.putInt("Counter", 15);
mPrefsEditor.commit();
}

error in saving the username at the launch of application in android

I am developing an android application in which i have to do the following thing
At the start of the app, first thing it should do is ask user to enter name and then through a welcome screen with that name.
Then When the app is used next time it should just give welcome screen (should not ask for name again)
I have created the code for the above.
I have used shared preference saved
My code is
private void SavePreferences(String key, String value){
SharedPreferences sharedPreferences = getSharedPreferences("MY_SHARED_PREF", MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.putString(key, value);
editor.commit();
}
private void LoadPreferences(){
SharedPreferences sharedPreferences = getSharedPreferences("MY_SHARED_PREF", MODE_PRIVATE);
String strSavedMem1 = sharedPreferences.getString("MEM1", "");
String strSavedMem2 = sharedPreferences.getString("MEM2", "");
textSavedMem1.setText(strSavedMem1);
textSavedMem2.setText(strSavedMem2);
}
}
But how to check whetehr user is already registered?
Thanks
Tushar

But how to check whetehr user is already registered?
When user starts application first time that time you will check if any preference value exists for name key.
Following snippet will help you
SharedPreferences sharedPreferences = getSharedPreferences("MY_SHARED_PREF", MODE_PRIVATE);
String namePrefrence = sharedPreferences.getString("uname", "");
if (namePrefrence.length() == 0) {
//User not registered!!
Show dialog where user will enter username
} else {
//User is registered!!
just show welcome screen
}

Well to use SharedPrefernces.. use this::
first declare it...
public static final String PREFS_NAME = "PrefernceNAme";
public static final String PREFS_ITEM = "PrefItemStored";
to get values from it, use:::
SharedPreferences preferences = getSharedPreferences(PREFS_NAME, MODE_PRIVATE);
mode = preferences.getString(PREFS_ITEM, "PrefItemStored");
and to add values in SharedPrefernces, use::
getSharedPreferences(PREFS_NAME, MODE_PRIVATE)
.edit()
.putString(PREFS_ITEM, value)
.commit();

Android ==> Preference?

my app crashes with a null pointer exception on the code below.
i have an xml preference file under res/xml/defaults.xml
Any idea why it's crashing?
public class Preference extends Activity {
public Preference()
{
}
public String getPreference(String key)
{
//it still crashes here
SharedPreferences settings = PreferenceManager.getDefaultSharedPreferences(this.getApplicationContext());
String result = settings.getString(key, null);
return result;
}
}

Preference files are not storead in project's /res/xml/defaults.xml
They are stored on the device in your application folder something like
/data/data/com.your.pkg/default.prefs
Try do not specify the file name, as you will have some problems with the preference files, like this OP had here
SharedPreferences preferences = PreferenceManager
.getDefaultSharedPreferences(context);
Then you will probably have to query
preferences.getString('weightPref', null);

Here's a sample code which shows how to save and retrieve Preferences. Here I am saving username and password in SharedPreferences.
SharedPreferences uPreferences = getSharedPreferences("CurrentUser", MODE_PRIVATE);
SharedPreferences.Editor editor; = uPreferences.edit(); //Instantiating editor object
protected void storeSharedPrefs(String username, String password) {
/*
* Storing in Shared Preferences
*/
editor.putString("username", username);
editor.putString("password", password);
editor.commit(); //Commiting changes
}
Retrieving username and password in another activity from SharedPreferences.
private SharedPreferences mSP;
mSP = getSharedPreferences("CurrentUser", MODE_PRIVATE);
String username = mSP.getString("username", null);
String password = mSP.getString("password", null);
Hope it helps..

Setting a value in the shared preferences:
Editor prefs = getSharedPreferences("Application_name", MODE_PRIVATE).edit();
prefs.putString("key", accountKey);
prefs.commit();
Getting the value from another activity:
String accountKey =
this.getSharedPreferences("Application_name", MODE_PRIVATE).
getString("key", null);
It would be nice if you access the variable by using some predefined handler, such as getString(R.string._key), instead of the hardcoded string "key".

Your Preferences should extend PreferenceActivity. Then you need to create a resource xml file for preferences, and reference that in your PreferenceActivity like so:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.preferences);
etc.
}
The preferences xml should have a PreferenceScreen as the top level element, and you can take advantage of all the different preference views Android makes available to you for setting preferences. This would be the most common, and elegant way to do it.