getSharedPreferences error in non-activity class

Question

I realize this issue has been touched on numerous times but nothing I try is working for me. I still get errors when trying to access SharedPreferences .

From the main Activity (McsHome) I am launch a variety of Dialogs to help the user add a location.

The first Dialog is below, this simply pops up a message stating a location needs to be added (PopupMessage.java):

public class PopupMessage extends DialogFragment {

    String message = "";
    AddLocation addLocation;


    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {

        addLocation = new AddLocation();

        // Use the Builder class for convenient dialog construction
        AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
        builder.setMessage(message)
               .setPositiveButton("Add Location", new DialogInterface.OnClickListener() {
                   public void onClick(DialogInterface dialog, int id) {
                       addLocation.show(getFragmentManager(), "PopupMsgFragment");
                   }
               })
               .setNegativeButton("Ok", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int id) {
              //
            };
        });
        // Create the AlertDialog object and return it
        return builder.create();
    }
}

This gives the user an option to add a location, when that button is clicked another dialog pops up (AddLocation.java):

public class AddLocation extends DialogFragment {

    EditText mcsDomain;
    EditText friendlyName;
    EditText password;
    ProcessLocation addLoc;
    String message = "";

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {

        AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
        LayoutInflater inflater = getActivity().getLayoutInflater();
        View layout = inflater.inflate(R.layout.add_location_dialog, null); // Pass null as the parent view because its going in the dialog layout
        mcsDomain = (EditText) layout.findViewById(R.id.mcsDomain);
        friendlyName = (EditText) layout.findViewById(R.id.friendlyName);
        password = (EditText) layout.findViewById(R.id.password);

        builder.setView(layout)
                .setTitle("Add/Update Location")
        // Add action buttons
               .setPositiveButton("Add/Update", new DialogInterface.OnClickListener() {
                   @Override

                   public void onClick(DialogInterface dialog, int id) {

                       // Passes the chosen location parameters to the ProcessLocation class
                       addLoc.processLocation(mcsDomain.getText().toString(),friendlyName.getText().toString(),password.getText().toString());

                   }
               })
               .setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
                   public void onClick(DialogInterface dialog, int id) {

                   }
               });      
        return builder.create();
    }

The AddLocation.java uses an XML layout which includes 3 EditText fields. The values of these are passed on to a third Class, ProcessLocation.java which includes the method processLocation() .

public class ProcessLocation {


    SharedPreferences domainToName;
    SharedPreferences nameToDomain;


     public void processLocation(String domain, String name, String password) {

            domainToName = getSharedPreferences("domainToName",  MODE_PRIVATE);
            nameToDomain = getSharedPreferences("nameToDomain",  MODE_PRIVATE);
        //  final Editor domainEdit = domainToName.edit();
        //  final Editor nameEdit = nameToDomain.edit();

            if (nameToDomain.contains(name)) {
                   System.out.println("Name Doesn't Exist");
                }

        }

}

I'm getting an error on the MODE_PRIVATE , I believe related to Context. I've been playing around with context for hours with no luck (or understanding). I know I'm popping up a couple of dialogs in a row. If I add "extends Activity" the error goes away but then the app crashes when trying to getSharedPreferences .

From going through the other posts I'm sure it's to do with passing the context from my McsHome.java activity but everything I've tried has failed.

Answer 1

First of all, in AddLocation you declare the member variable addLoc , but you never assign it to anything. If you did get this to compile, it would throw a NullPointerException here:

addLoc.processLocation(mcsDomain.getText().toString(), friendlyName.getText().toString(),
        password.getText().toString());

getSharedPreferences() is a method of the Context class. In ProcessLocation.processLocation() you are trying to call it. This method doesn't exist in the ProcessLocation class.

You need to do the following:

1) ProcessLocation needs to have a Context reference, so that it can call getSharedPreferences() . The easiest way to do this is to declare a member variable in ProcessLocation of type Context and have it initialized in the constructor of ProcessLocation . Like this:

public class ProcessLocation {
    Context context;
    SharedPreferences domainToName;
    SharedPreferences nameToDomain;
    // Constructor
    ProcessLocation(Context context) {
        this.context = context;
    }

2) You need to create an instance of ProcessLocation . In AddLocation , before using the variable addLoc you will need to initialize it. Like this:

    // Create instance of ProcessLocation and pass it the activity (Activity is a Context)
    addLoc = new ProcessLocation(getActivity);

3) Use the Context in ProcessLocation.processLocation() , like this:

    public void processLocation(String domain, String name, String password) {
        domainToName = context.getSharedPreferences("domainToName",  Context.MODE_PRIVATE);
        nameToDomain = context.getSharedPreferences("nameToDomain",  Context.MODE_PRIVATE);
        ...
    }

It is late and I'm tired and I didn't put this through a compiler, so please forgive me if I left out a comma or a semicolon or spelled something wrong. Hopefully you get the drift. Good luck!