Develop Reference

How do I access Android SharedPreferences from a static method in a class without passing in a context reference?

I have just one class where I need to access SharedPreferences:
public class MyUtils {
public static String packageMe(Object input){
// do stuff here
// need SharedPreferences here
}
public static Object unpackageMe(String input){
// do stuff here
// need SharedPreferences here
}
}
I tried this:
public class MyUtils extends Activity
But, as you know, I cannot access SharedPreferences from a static method.
I thought about passing in the context to the static methods, but that extends the number of classes out to four that I will need to modify, and the classes are already extending AsyncTask:
public class SomeClass01 extends AsyncTask {
#Override
protected Object doInBackground(Object[] params){
MyUtils.packageMe(abc_123_object);
// do stuff here
}
}
So, I thought that maybe I could pass the context into those four classes. However, there are a couple dozen classes that I would need to modify that use those four classes, that in turn use that single class.
public class SomeTopClass extends FragmentActivity implements x, y, z {
new SomeClass01.execute(abc_123_object);
// do stuff here
}
I don't know if I want to be passing a context reference that deep into my code.
I saw here on StackOverflow about putting a reference to the SharedPreferences in my abc_123_object model, but there are quite a few objects I use (other than abc_123_object) and I don't want to have to jerry-rig so many classes.
So, is there a way for me to do this without modifying dozens of classes and passing context references all around my code, or am I stuck?
Thanks

Create static variable in your Application class.
public class MyApp extends Application{
public static Context context;
#Override
public void onCreate() {
context = this;
}
}
Then use it when you need.
public static String packageMe(Object input){
// do stuff here
// need SharedPreferences here
// context = MyApp.context
}

As Dusan mentioned, using an application class is an easy way to do this:
In your application class:
private static MyApplication sInstance = null;
private SharedPreferences mPrefs
public static MyApplication getApp()
{
return sInstance;
}
public SharedPreferences getSharePreferences()
{
return mPrefs;
}
in onCreate():
sInstance = this;
mPrefs = getSharedPreferences(PREF_FILE, MODE_PRIVATE);
Then in your code simply do:
MyApplication.getApp().getSharePreferences();
Your Application's onCreate() is guaranteed to be executed before any activity is created, so unless you are doing something really weird, it should be safe.

Custom Class extends Application for Singleton Purposes

I tried to create custom class to fetch some values from SharedPreferences.
My aim is to reach to that values from any class.
I am getting null Pointer exception on
SharedPreferences prefs = getApplicationContext().getSharedPreferences("UserFile", MODE_PRIVATE);
My code is as below;
public class UserInfo extends Application {
private String token;
private String SAVED_USERNAME;
public UserInfo() {
SharedPreferences prefs = getApplicationContext().getSharedPreferences("UserFile", MODE_PRIVATE);
token = prefs.getString("Token", null);
}
public String getToken() {
return token;
}
}
What might be the wrong?

Usually Android components are initialized during their lifecycle. In this particular case you can't access application Context and SharedPreferences because they're not initialized yet.
Second problem might be (thanks to my crystall ball) that you did not added your Application to AndroidManifest
So, your first thought might be to move initialization code from constructor to onCreate. This would solve this particular problem.
However, it's a bad practice to do what you're doing. Because there can be only 1 Application component per application. This will limit you to 1 such singleton per app. Consider using Application to provide application Context as singleton and create another singleton for providing UserInfo.
No examples, please exercise yourself.

Just have this method in a util class. No need to extend application.
public static String getToken(Context context) {
return PreferenceManager.getDefaultSharedPreferences(context).getString("Token", null);
}

There is a rule in android - don't use constructor of app component: Activity/Fragment/Application/Service... there is onCreate() method, because in your constructor context will be null. So move your code to onCreate(). Also you need set your UserInfo as application in Manifest.

You don't create constructor of Application class instead, use the code in onCreate():
#Override
public void onCreate() {
super.onCreate();
SharedPreferences prefs = getApplicationContext().getSharedPreferences("UserFile", MODE_PRIVATE);
token = prefs.getString("Token", null);
}
and use it from any activity:
UserInfo userInfo = (UserInfo)getApplication();
String token = userInfo.getToken();

public class MyApp extends Application {
private static MyApp _instance;
#Override
public void onCreate() {
super.onCreate();
_instance = this;
}
public static MyApp getInstance(){
return _instance;
}
public String getToken() {
return getSharedPreferences("UserFile", MODE_PRIVATE).getString("Token", null);
}
}
In your manifest:
<application
android:name="your.package.MyApp"
>
If you whant use :
String token = MyApp.getInstance().getToken();

Make sure you have registered this class in your AndroidManifest.XML file.
<application android:name=".UserInfo"
...
/>
Note: Your way for accessing shared preferences does not seem good. I rather myself declare a class named PreferencesHelper and put all preferences stuff there.
public class PreferencesHelper{
private SharedPreferences mPrefs;
public PreferencesHelper(Context context){
this.mPrefs = context.getSharedPreferences("name", Context.MODE_PRIVATE);
}
public getToken() {
return mPrefs.getString("Token", null);
}
public String setToken(String token) {
mPrefs.edit().putString("Token", token).apply();
}
}

How to Access Android Custom Application Object in simple Java Class which Also has ApplicationContext object?

I have created a custom application class like this:
class A extends android.app.Application{
public String abc = "xyz";
}
And I have a simple java class
class B {
private appContext;
// This constructor is called from activity.
B(Context ctx){
this.appContext = ctx;
}
private void foo(){
// want to access Class A's abc String vairable Here...HOW TO DO THAT?????
}
}
How to access Class A's abc String vairable in foo method.

You can get the Application class with getApplicationContext from Context with the good casting
((A) this.ctx.getApplicationContext()).abc;

The Application class in Android is a singleton and therefore so is your derived class. Android will create just one instance of your class A when it starts your application. Just change
class A extends android.app.Application {
public String abc = "xyz";
}
to
class A extends android.app.Application {
public static String abc = "xyz";
}
and you can reference it from anywhere like this:
String foo = A.abc;

Instead of passing a Context, try passing an instance of the Application class instead.
Something like:
class B {
private Application app;
// This constructor is called from activity.
B(Application ctx){
this.app = ctx;
}
private void foo(){
app.abc; //Do what you want
}
}
And call B like:
B b = new B(getApplication());
Make sure that this is in onCreate() or later.

Looks like you are already passing the application context as a parameter and initializing it in the constructor. So all you have to now is to use the context variable to access abc of A like the following way: ((A) this.appContext).abc;

Android - Global variables?

I need to stock some datas in my application.
I know that i can do it like this:
class:
public class MyApplication extends Application {
private String someVariable;
public String getSomeVariable() {
return someVariable;
}
public void setSomeVariable(String someVariable) {
this.someVariable = someVariable;
}
}
Implementation:
MyApp appState = ((MyApp)getApplicationContext());
String state = appState.getSomeVariable();
This is working if i'm in an activity.
But if i'm in a class not extended from Activity, how can I access at my datas?
thanks in advance for your help!

You can use a Singleton design pattern. You can then use it anywhere, because it has static access.
public class SingletonClass {
private static SingletonClass _instance = null;
private int _value = 0;
private SingletonClass() {
}
public static SingletonClass getInstance() {
if (_instance == null)
_instance = new SingletonClass();
return _instance;
}
public int getValue() {
return _value;
}
public void setValue(int value) {
_value = value;
}
}
and then access it like this:
SingletonClass.getInstance().getValue();
Note: This is a good and easy workaround for some programming problems, but use it very wisely.. it comes with it's problems

Use SharedPrefrences
http://developer.android.com/guide/topics/data/data-storage.html

Perhaps by injecting all the required for a class data via constructor or special setter, I would suggest former one. (Constructor Injection vs. Setter Injection)
There are more solutions like static fields but personally I do not like this approach since statics sometimes makes unit testing a bit messy.
BTW, what kind of variables you want to share?

I use, it may be gruesome to some, a class with static variables, that you can retrieve from every class in the app.
Just create a class with all the field as static, and you can use them throughout your app. It doesn't get erased, only when stopping the app.
You could also just add static variables to your application class.

You can use static methods (or variables if they are public). It's really a little messy, but if you group them (methods) in the right way you'll earn happinnes and satisfaction )
static public int getSomeInt(){
//something
}
And then anywhere in your app use
int x=MyApplication.getSomeInt();
By the way, using this style, you don't need to extend Application class. It's better to create an abstract class for such purposes.

Pass the context of your activity as a param to the method or class:
// ...
public void doStuff(Context context) {
// for example, to retrieve and EditText
EditText et = context.findViewById(R.id.editText1);
}
then, on your activity, you would do:
// ...
MyClass myClass = new MyClass();
// ...
myClass.doStuff(this);
// ...

Creating an Object accessible by all Activities in Android

I'm trying to create an ArrayList of Data containing Objects (Like a list of Addresses and properties (pretty complex)) and am wondering: How can I make an Object accessible (and editable) by all Activities and not just the one it was instanciated in?
Basically this:
Create Array in Activity 1
Access same Array in Activity 2 and 3
???
Profit.

The easiest way to do this is by creating an Singleton. It's a kind of object that only can be created once, and if you try to access it again it will return the existing instance of the object.
Inside this you can hold your array.
public class Singleton {
private static final Singleton instance = new Singleton();
// Private constructor prevents instantiation from other classes
private Singleton() {
}
public static Singleton getInstance() {
return instance;
}
}
Read more about singleton:
http://en.wikipedia.org/wiki/Singleton_pattern

You can extend the application class. And add your arrays there.
You can access the instance of the class by using this command
MyApplication appContext = (MyApplication)getApplicationContext();

Well you can create a Constant class and declare you ArrayList as a static variable.
1.)
Class ConstantCodes{
public static ArrayList<MyClass> list = new ArrayList<MyClass>;
}
This will be accessible from everywhere you want by just ConstantCodes.list
2.) You can extend your class by Application class like this
class Globalclass extends Application {
private String myState;
public String getState(){
return myState;
}
public void setState(String s){
myState = s;
}
}
class TempActivity extends Activity {
#Override
public void onCreate(Bundle b){
...
Globalclass appState = ((Globalclass)getApplicationContext());
String state = appState.getState();
...
}
}

you should make it static and access it from any other activity.....

how about use a static keyword ?
public static SomeClass someObject
in your activity class that initiate your object

1- In your Activity1, déclare your array in public static
public static ArrayList<HashMap<String, String>> myArray = new ArrayList<HashMap<String, String>>();
2- In your Activity2, Activity3, etc. access to your ArrayList
Activity1.myArray

You can create a java file x beside other java files.
x file contains static method which used to access the class method without instantiate it.
Now make a method called createVariable() and declare variable which you want to make it Global.
Now make a method called getVariable() which returns the Global variable.
At which point you want to create global variable, call className.createVariable().
And to get access to that variable call className.getVariable().
Here is my example for Database class.
public class GlobalDatabaseHelper{
static DatabaseHelper mydb;
public static DatabaseHelper createDatabase(Context context)
{
mydb = new DatabaseHelper(context);
return mydb;
}
public static DatabaseHelper returnDatabase()
{
return mydb;
}
}