I am trying to save the date of file parsing, so that when next time user, opens the application, the date can be checked against the last parsing date.
I am using shared preference to save the data and retrieve it, but getting error. Here is the code :
SharedPreferences settings = getPreferences(0); String today = new Date(System.currentTimeMillis()).toString(); SharedPreferences.Editor edit = settings.edit(); System.out.println("******** Today : " + today); edit.putString("lastdate", today); String fetch = settings.getString("lastdate", "0"); System.out.println("******** Fetch : " + fetch); txtTest.setText(fetch);
But I am getting null pointer error, am I missing something?
Many applications may provide a way to capture user preferences on the settings of a specific application or an activity. For supporting this, Android provides a simple set of APIs.
Preferences are typically name value pairs. They can be stored as “Shared Preferences” across various activities in an application (note currently it cannot be shared across processes). Or it can be something that needs to be stored specific to an activity.
Shared Preferences: The shared preferences can be used by all the components (activities, services etc) off the applications.
Activity handled preferences: These preferences can only be used with in the activity and can not be used by other components of the application.
The shared preferences are managed with the help of
getSharedPreferences method of the
Context class. The preferences are stored in a default file(1) or you can specify a file name(2) to be used to refer to the preferences.
(1) Here is how you get the instance when you specify the file name
public static final String PREF_FILE_NAME = "PrefFile"; SharedPreferences preferences = getSharedPreferences(PREF_FILE_NAME, MODE_PRIVATE);
MODE_PRIVATE is the operating mode for the preferences. It is the default mode and means the created file will be accessed by only the calling application. Other two mode supported are
MODE_WORLD_READABLE other application can read the created file but can not modify it. In case of
MODE_WORLD_WRITEABLE other applications also have write permissions for the created file.
(2) The recommended way is to use by the default mode, without specifying the file name
SharedPreferences preferences = PreferencesManager.getDefaultSharedPreferences(context);
Finally, once you have the preferences instance, here is how you can retrieve the stored values from the preferences:
int storedPreference = preferences.getInt("storedInt", 0);
To store values in the preference file
SharedPreference.Editor object has to be used.
Editor is the nested interface of the
SharedPreferences.Editor editor = preferences.edit(); editor.putInt("storedInt", storedPreference); // value to store editor.commit();
Editor also support methods like
clear() to delete the preference value from the file.
The shared preferences can be used by other application components. But if you do not need to share the preferences with other components and want to have activities private preferences. You can do that with the help of
getPreferences() method of the activity. The
getPreference method uses the
getSharedPreferences() method with the name of the activity class for the preference file name.
Following is the code to get preferences
SharedPreferences preferences = getPreferences(MODE_PRIVATE); int storedPreference = preferences.getInt("storedInt", 0);
The code to store values is also same as in case of shared preferences.
SharedPreferences preferences = getPreference(MODE_PRIVATE); SharedPreferences.Editor editor = preferences.edit(); editor.putInt("storedInt", storedPreference); // value to store editor.commit();
You can also use other methods like storing the activity state in database. Note Android also contains a package called
android.preference. The package defines classes to implement application preferences UI.
To see some more examples check Android’s Data Storage post on developers site.