Develop Reference

Weird thing on sharedPreferences while loading the highest score

I am using SharedPreferences to store and load the highest score on my game. The problem that I found is that when I close the emulator from the 'X' mark it didn't save the highest score, but if I firstly put the app in the background and then close it (within the emulator or from the 'X' mark) it will save and load the best score. Here is the code that I use:
//save the highscore
SharedPreferences prefs = this.getContext().getSharedPreferences("BEST", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = prefs.edit();
editor.putInt("key", best);
editor.commit();
//load the highscore
SharedPreferences prefs = this.getContext().getSharedPreferences("BEST", Context.MODE_PRIVATE);
best = prefs.getInt("key", 0);
note: I have tested the game on two acutal devices ( LG Optimus L2 and Samsung Galaxy A3) and on both of them everything works normally. It is something that i shouldn't worry about?
EDIT: I forgot to mention that I had to use "Clean Project" after I renamed the folder of the project directly and from here I encountered some errors. Maybe that has something to do with it.

Whether your score gets saved depends on where you run your code to save it (which looks completely fine). If you, for example, save it in the onStop() method of an Activity, then putting it in the background will save it properly.
Shutting down the emulator by closing its window probably kills it quite violently, in which case it can very easily be the case that your app doesn't receive the lifecycle callbacks it normally does, it just gets terminated immediately, hence your code that would save to SharedPreferences doesn't get to run. On a real device this sort of immediate shutdown would be the equivalent of shutting down the phone by holding the power button or taking out the battery, which is not something you can prepare for.
TL;DR: this seems normal, I wouldn't worry about it.

Sharedpreference between applications with the same sharedUserId

I'm working on a project where I have a core application and multiples plugins which are different apks. I would like to share some data between my different modules (for ex. the name of the user or his email address). I tried to give them all the same sharedUserId by adding it to their manifest :
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.giom.mymodule1"
android:sharedUserId="com.giom">
My modules are really similar and both save and try retrieve their sharedpreferences the same way :
Context mainAppContext = getActivity().getApplicationContext().createPackageContext("com.giom.mainapp", Context.MODE_WORLD_READABLE | Context.MODE_WORLD_WRITEABLE);
SharedPreferences sharedPreferences = mainAppContext.getSharedPreferences("sharedpreferences", Context.MODE_WORLD_READABLE | Context.MODE_WORLD_WRITEABLE);
sharedPreferences.edit().putString("EMAIL", email).commit();
And
Context mainAppContext = getActivity().getApplicationContext().createPackageContext
("com.giom.mainapp", Context.MODE_WORLD_READABLE | Context.MODE_WORLD_WRITEABLE);
SharedPreferences sharedPreferences = mainAppContext.getSharedPreferences("sharedpreferences", Context.MODE_WORLD_READABLE | Context.MODE_WORLD_WRITEABLE);
String email = sharedPreferences.getString("EMAIL", null)
Both codes are from my PreferenceActivities which are FragmentActivity. The problem is this seems to be working ; for example if I change the value in one of the modules and reboot the phone the other is changed. But if I open one of the activities, then the other, change the value in one of them and come back to the other I will still get the old one until I reboot. It's working like if there was some kind of cache...
My intuition is that I'm not using the right Context and that I should replace getActivity() by something else but I don't know what...
Thanks in advance for your help.
PS: I read that this method was depreciated so if you have any idea of how I should share my data feel free to tell me :)

Ok, found the answer here : https://stackoverflow.com/a/11025235/3628452
The getSharedPreferences method appears to check for a .bak file to
load the preferences from. This is why it says in the documentation
that it will not work across multiple processes; to minimize I/O, it
loads the prefs ONCE when you grab them and only backs them up when
you close your application/activity
Which means that if I don't open/close my modules I'll still have the data from the bak file from when I opened it...

Writing to shared preferences too slow?

I have created a service that writes some information about a widget once a user places it on home screen(the info is picked up from the confutation activity)..i also write down the number of widgets the user has set up.
Once the user removes the widget i delete that info in the shared preferences.
What i have experienced is that if user places for example 2 widgets, then removes one, then places one again, doing all those actions fast, the shared preferences file gets inconsistent values in it. Sometimes it works ok but most of the time i get stuck with wrong values in it.
I am using apply(), i've tried with commit but same thing happens.
The values i store in the shared preferences are crucial for the system to work, without it the widgets are useless since they are backed up by info from internet based on the user configuration which is written in preferences.
Is switching to a database solution more reliable or any other viable solution which will fix this "race condition"? (maybe forcing my own mechanism of synchronization, but as far as i've understood from docs, apply() is already synchronized, and the read/write should first go to RAM which should make it fast and i shouldnt be experiencing any problems like this since the user cant physically manage to delete a widget and place a new one faster then 2-3 seconds top!)

Try using the synchronized keyword in working with the SharedPreferences itself. For example, here is a method that could be used when setting an application String in the SharedPreferences of an Android app:
public synchronized static void setAppString(Context context, String pref,
String val) {
SharedPreferences sp = context.getSharedPreferences(
APP_PREFS_UNIQUE_ID, Context.MODE_PRIVATE);
Editor editor = sp.edit();
editor.putString(pref, val);
editor.commit();
}
For few/simple key-value pairs, you might not need the overhead of a database paradigm.

Migrate from getSharedPreferences(custom file) to getDefaultSharedPreferences()

When I originally wrote and published my app, I was using a custom written activity to handle application settings. I used custom file name to store shared preferfences, like this:
getSharedPreferences("custom_settings_file",MODE_PRIVATE);
But now I'm refactoring my app and I would like to implement PreferenceActivity or PreferenceFragment and an xml file with PreferenceScreen section. Every tutorial or example that I've seen is using
getDefaultSharedPreferences(context);
to retrieve shared preferences, because PreferenceActivity assumes default filename to store preferences and there's no way to tell it to use a different one(at least I couldn't find one after an hour of searching and reading documentation).
So now I have a problem. If I just simply use the new default file, existing users of my app will lose their settings when they update the app, because the new application will not know anything about "custom_settings_file". What would be the best way to move the data from an old file to a new one on app update?
Here are the possible options that I could come up with:
Extend Application class and implement a piece of code in onCreate() so that every time my app is launched, it would check for existence of "custom_settings_file" and move it's contents to the new one. But running a block of code on every app launch seems like wasting too much processing resources for an operation that only needs to run once.
Just notify the user that their old settings are gone. But obviously this is not acceptable.
Is there a better solution, than option 1? Perhaps someone has already faced a similar problem?

What is preventing you from doing number 1 only once?
Just add a "migration" boolean to the new sharedpreferences.

If you also load the xml preference file then you can try this:
PreferenceManager.setDefaultValues(context, YOUR_PREFERENCE_NAME, MODE_PRIVATE, R.xml.preference_file, false);
If not (you want to add each preference item dynamically in your code) then you can do like this:
PreferenceManager pm = getPreferenceManager();
pm.setSharedPreferencesMode(MODE_PRIVATE);
pm.setSharedPreferencesName(YOUR_PREFERENCE_NAME);
In case you still want to use the defaultSharedPreference and process the migration then ... I'm writing this and I see Nicklas's answer, so I'm done here.

Could you add value in your new SharedPreferences that records whether you are a new install or an upgrade. If you don't have the setting in your sharedpreferences, check to see if you have an old preferences file in the way you were before. Then convert those preferences to your new method, and set your private setting indicating that it's been upgraded. Then just set the new value indicating the new state and you won't need to check your old preferences any more.

SharedPreferences not being updated

I am having an odd issue in which the SharedPreferences are not being updated upon returning to an app. Here's the scenario:
I have two projects that use the same shared preferences. Project1 and Project2. They are separate but related apps. They are signed with the same key and use sharedUserId to share information.
Project1 opens Project2.
Project2 retrieves the SharedPreferences file and writes to it via this method:
Context prefsContext = c.createPackageContext(packageNameOfProject1, Context.CONTEXT_IGNORE_SECURITY);
SharedPreferences prefs = prefsContext.getSharedPreferences(fileName, Context.MODE_PRIVATE);
SharedPreferences.editor editor = prefs.edit();
editor.putBool("bool1", value1);
editor.putBool("bool2", value2);
...
editor.putBool("boolN", valueN);
editor.apply();
Once that is done, I return to Project1 by calling finish().
Project1 then reads the data like so:
SharedPreferences prefs = getSharedPreferences(getPreferencesFileName(), Context.MODE_PRIVATE);
Boolean value1 = prefs.getBoolean(fileName, false);
Boolean value2 = prefs.getBoolean(fileName, false);
...
Boolean valueN = prefs.getBoolean(fileName, false);
Map<String, ?> mappings = prefs.getAll();
Set<String> keys = mappings.keySet();
for(String key : keys) {
log.d(TAG, "_____");
log.d(TAG, "Key = " + key);
log.d(TAG, "Value = " + mappings.get(key));
}
The problem is the values are not updated in Project1. I can tell based off the logs at the end that the file isn't even generating mappings. However, I can verify that the xml is being updated. If I force stop the app then restart it, all the mappings are there in Project1. All the values are correct. However, I need them updated when the user leaves Project2. I feel like there's something I'm missing here but can not spot it.
The only things I have been able to find on the subject is:
SharedPreferences.Editor not being updated after initial commit
SharedPreferences value is not updated
These don't help as I'm already doing that.
I have WRITE_EXTERNAL_STORAGE set in both manifests. The fileName is the same (else I wouldn't be able to read the file when I reenter the app).
EDIT:
I should note that I did try to do editor.commit() instead of editor.apply() as I thought I was facing a race condition. The problem still persisted. I'm thinking that for some reason, the old reference to the SharedPreference in Project1 is being used instead of a new one even though I'm lazy-loading it each time.
EDIT2:
Ok, to further test to see what id going on. I decided to try the opposite direction.
In Project1 I do:
Float testFloat (float) Math.random();
Log.d("TEST_FLOAT", "Project1: TEST_FLOAT = " + testFloat);
prefs.edit().putFloat("TEST_FLOAT", testFloat).commit();
In Project2 I do:
Log.d("TEST_FLOAT", "Project2: TEST_FLOAT = " + prefs.getFloat("TEST_FLOAT", 0.0f));
I then go back and forth between the two like so: Project1->Project2->Project1->Project2->Project1->Project2 and here is the logcat result:
Project1: TEST_FLOAT = 0.30341884
Project2: TEST_FLOAT = 0.30341884
Project1: TEST_FLOAT = 0.89398974
Project2: TEST_FLOAT = 0.30341884
Project1: TEST_FLOAT = 0.81929415
Project2: TEST_FLOAT = 0.30341884
In other words, it's reading and writing to the same file. However, it's keeping the mapping that it had when it was first opened it in the project. Even though I close the project, the mapping remains until the application is force stopped.

EDIT: I'm still getting upvotes on this answer even though it recommends a method that has since been deprecated. If you need consistent data through multi-process, then you need to use something other than SharedPreferences like a ContentProvider backed by a file system or database.
https://developer.android.com/reference/android/content/Context#MODE_MULTI_PROCESS
Final answer:
Replace
getSharedPreferences(fileName, Context.MODE_PRIVATE);
with
getSharedPreferences(fileName, Context.MODE_MULTI_PROCESS);
As per document:
Context.MODE_MULTI_PROCESS
SharedPreferences loading flag: when set, the file on disk will be
checked for modification even if the shared preferences instance is
already loaded in this process. This behavior is sometimes desired in
cases where the application has multiple processes, all writing to the
same SharedPreferences file. Generally there are better forms of
communication between processes, though.
This was the legacy (but undocumented) behavior in and before
Gingerbread (Android 2.3) and this flag is implied when targeting
such releases. For applications targeting SDK versions greater than
Android 2.3(Gingerbread), this flag must be explicitly set if desired.
I knew there was a simple oversight in this.

Try to call editor.commit(); instead of editor.apply();. Normally they should do the same, but I noticed there some weird behaviour sometimes.

From the SharedPreferences documentation the method "apply()" writes asynchronously (delayed) to the file and the method "commit()" writes the information synchronously (immediatly) to the file.
Also from the documentation, they say that you don't need to wary about the activity life cycle while using any of the above methods, as they ensure the "apply()" writes are completed before status changes, if they are running in the same system process.
However, as you are using two different projects, they run in two different processes and you can't be sure that "apply()" on project 2 will be concluded before the "onResume()" starts on project 1.
I suggest that you try "commit()" instead of "apply()" to force synchronous write. If this don't solve the issue, you can add a delay of a couple of seconds before reading the preferences in project 1, just to check if the issue is related to this delayed write.
--EDITED--
To debug the issue let's do the following:
1-In Eclipse Select/Add the view "File Explorer" and navigate to the directory:
/data/data/[your package name]/shared_prefs
your package name should be something like "com.myproject.shared"
2-Select the file with your saved preferences and press the button "download to PC".
3-Check if file contents match your expectations.
good luck.