Question

I want to pass strings to all pages in my android app. When the user logs in I save userName and others to strings. I want to send the strings over multiple pages. How can I do that?

I have tried to send it through Intent

Intent myIntent = new Intent(view.getContext(), Help.class);  
myIntent.putExtra("userName", userNameString);
startActivityForResult(myIntent, 0); 

But when I go to another page I dont want to keep sending the data through Intent every time.

I have tried to get it from the class where I parse and put them in strings

HomeScreen home = new HomeScreen();
String userName= home.userNameString;

But since i am creating a new instance of the HomeScreen then userNameString is null

Any help will be greatly appreciated

Answer 1

Beware of using a static or instance variable to hold this state as the memory state of an Android application can be in flux. Data only stored in memory can be destroyed without your knowledge if your application process is killed while in the background.

The simplest mechanism would be to persist your data into SharedPreferences that you can access from any place in the application. So, first you save the string that you get from login (this is called inside an Activity, FYI):

//Write the username string to preferences
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
prefs.edit().putString("userName", userNameString).commit();

Then elsewhere in your application (i.e. other Activity instances) can read that string:

//Read the username string
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
String userName = prefs.getString("userName", "");

With SharedPreferences, your values are actually persisted, meaning they will live forever on disk and won’t go away just because your application’s memory is reset (this is usually an advantage, especially for login information). Because of this, you will also need to remove the string when your user “logs out” like so:

//Remove the username string from preferences
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
prefs.edit().remove("userName").commit();

There are also methods like contains() to allow you to check if the value is currently saved (is the user logged in?), etc.