How to create a global variable in android?

Question

In my android application I need a place for putting the variable member id . The problem is , it is getting from the online API and I need to find a way to store / retrieve it

I have tried to put it in a custom class , but the problem is , it will lose if I kill the activity, I have also know that there is a way to extends the application.

So I would like to know what is the best way to store global variable?

I have to implment:

Save the variable on onSaveState
Save it on sharepref
Save it manually
Retrieve it manually

Thanks

Update: Thanks for reply. If I have just 3 variable (simple data e.g. a boolean , a phrase ), and I need it after app restart , should I simply use share pref to store it? What is the drawback of it? e.g. Will it harmful to the performance? thanks

Please, don't look at singleton [anti-pattern](http://en.wikipedia.org/wiki/Anti-pattern). — amit, Feb 16 '14 at 11:01

Ajay S · Accepted Answer · 2014-02-16T12:43:51.707

29

You can create the global variable in android by declaring them in the class which extend the Application class.

Something like this.

class MyAppApplication extends Application {

    private String mGlobalVarValue;

    public String getGlobalVarValue() {
        return mGlobalVarValue;
    }

    public void setGlobalVarValue(String str) {
        mGlobalVarValue = str;
    }
}

MainActivity.java

class MainActivity extends Activity {
    @Override
    public void onCreate(Bundle b){
        ...
        MyAppApplication mApp = ((MyAppApplication)getApplicationContext());
        String globalVarValue = mApp.getGlobalVarValue();
        ...
    }
}

Update

This hold the value until your application is not destroyed. If you want to keep your values save even after your application instance destroy then you can use the SharedPreferences best way to do this.

Learn about the SharedPrefernces from here : http://developer.android.com/reference/android/content/SharedPreferences.html

edited Feb 16 '14 at 12:43

answered Feb 16 '14 at 11:08

Ajay S

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1

what if i want to access these values outside the activity, say in some other layer ? i can't do getApplicationContext() there. AND i should not pass Context object around in different layers. – Punith Raj Jun 23 '15 at 12:08
1

What about STATIC variable??? – Gurgen Hakobyan Mar 31 '16 at 16:33
@GurgenHakobyan I think that we get the same instance of ```MyAppApplication``` when call ```getApplicationContext()``` and use static variables has the same effect. – JCarlosR Aug 13 '16 at 19:38
How about performance when using this global variable ? – questionasker Feb 08 '17 at 13:13

score 6 · Answer 2 · edited May 23 '17 at 12:02

If you need a global variable, which is shared between multiple activities and survives their lifecycle changes, but is otherwise not persisted and would not survive an application restart, the method suggested in the first answer (extending Application and putting it there) is ok.
If you need a persisted global setting, which should also survive an application restart, then you should use one of the other methods suggested. SharedPreferences is probably the easiest to use.

See also this Stack Overflow question: What's the best way to share data between activities?

score 2 · Answer 3 · answered Feb 16 '14 at 11:01

2

You can store it in a SharedPreferences, and create a sharedpreferenceHelper class to retrieve/store it.

answered Feb 16 '14 at 11:01

StarsSky

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score 1 · Answer 4 · answered Feb 16 '14 at 11:12

1

Its always better to store values which you want to use multiple times in one of the following ways:-

Shared Preferences
Singleton classes
Write it to a file
SQLite Database
Store on the web-server

answered Feb 16 '14 at 11:12

Atish Agrawal

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I disagree. It is only better, if the data is also required on restart of the app. If not, and the data for instance needs to be fresh on a fresh startup, the answer made by TGMCians fits the need. – Bart Burg Jun 02 '17 at 09:12

How to create a global variable in android?

4 Answers4

Update

Linked