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Android Studio – How do I call a method from fragment to class?

I have a fragment and I want to call to a method which is in a AppConfig.class. But when I run the application there was a error came as " Attempt to invoke interface method 'android.content.SharedPreferences$Editor android.content.SharedPreferences.edit()' on a null object reference". How do I solve this error?

Here is my code in AppConfig.class

 public void updateUserLoginStatus(boolean status){

    SharedPreferences.Editor editor= sharedPreferences.edit();
    editor.putBoolean(context.getString(R.string.pref_is_user_login),status);
    editor.apply();

}

Here is my code in Fragment

appConfig.updateUserLoginStatus(false);
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2

Answers


  1. 0

    You need to create a Appconfig object in your calling Activity/fragment.

    Example –

    Appconfig appconfig = new Appconfig ();
    appconfig.updateUserLoginStatus(false);

    Null pointer exception shows that, you have just declared a global variable in your class for appConfig but not initialised it.

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  2. 0

    If you want to access Shared Preference as default file name from all activities/fragment then consider to use

    getDefaultSharedPreferences(Context context)

    Gets a SharedPreferences instance that points to the default file that is used by the preference framework in the given context.

    So in AppConfig class you can implement a void where you can pass Context from different Activities to get getDefaultSharedPreferences .

    private static Context context;
static SharedPreferences sharedPreferences;

public static void init(Context ctx){
    context = ctx;
    sharedPreferences = PreferenceManager.getDefaultSharedPreferences(context);

}

    Before call updateUserLoginStatus , you have to call AppConfig.init() .

    From Activity –

         AppConfig.init(this);

    AppConfig appConfig = new AppConfig();
    appConfig.updateUserLoginStatus(false);

    From Fragment –

         AppConfig.init(getContext());
     AppConfig appConfig = new AppConfig();
     appConfig.updateUserLoginStatus(false);
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