Professional Android 4 Application Development

242 x CHAPTER 7 FILES, SAVING STATE,AND PREFERENCES
}
startActivityForResult(i, SHOW_PREFERENCES);
return true;
}
}
return false;
All the code snippets in this example are part of the Chapter 7 Earthquake Part 2
project, available for download at www.wrox.com.
PERSISTING THE APPLICATION INSTANCE STATE
To save Activity instance variables, Android offers two specialized variations of Shared Preferences.
The first uses a Shared Preference named specifically for your Activity, whereas the other relies on a
series of lifecycle event handlers.
Saving Activity State Using Shared Preferences
If you want to save Activity information that doesn’t need to be shared with other components
(e.g., class instance variables), you can call Activity.getPreferences()without specifying a
Shared Preferences name. This returns a Shared Preference using the calling Activity’s class name as
the Shared Preference name.
// Create or retrieve the activity preference object.
SharedPreferences activityPreferences =
getPreferences(Activity.MODE_PRIVATE);
// Retrieve an editor to modify the shared preferences.
SharedPreferences.Editor editor = activityPreferences.edit();
// Retrieve the View
TextView myTextView = (TextView)findViewById(R.id.myTextView);
// Store new primitive types in the shared preferences object.
editor.putString(“currentTextValue”,
myTextView.getText().toString());
// Commit changes.
editor.apply();
Saving and Restoring Activity Instance State Using the
Lifecycle Handlers
Activities offer the onSaveInstanceState handler to persist data associated with UI state across
sessions. It’s designed specifically to persist UI state should an Activity be terminated by the run
time, either in an effort to free resources for foreground applications or to accommodate restarts
caused by hardware configuration changes.