Saving Key-Value Sets

标签：android数据存储   sharedpreference   

If you have a relatively small collection of key-values that you‘d like to save, you should use the SharedPreferences APIs. ASharedPreferences object points to a file containing key-value pairs and provides simple methods to read and write them. Each SharedPreferences file is managed by the framework and can be private or shared.

This class shows you how to use the SharedPreferences APIs to store and retrieve simple values.

Note: The SharedPreferences APIs are only for reading and writing key-value pairs and you should not confuse them with the Preference APIs, which help you build a user interface for your app settings (although they use SharedPreferences as their implementation to save the app settings). For information about using the Preference APIs, see the Settings guide.

Get a Handle to a SharedPreferences

You can create a new shared preference file or access an existing one by calling one of two methods:

• getSharedPreferences() — Use this if you need multiple shared preference files identified by name, which you specify with the first parameter. You can call this from any Context in your app.
• getPreferences() — Use this from an Activity if you need to use only one shared preference file for the activity. Because this retrieves a default shared preference file that belongs to the activity, you don‘t need to supply a name.

For example, the following code is executed inside a Fragment. It accesses the shared preferences file that‘s identified by the resource string R.string.preference_file_key and opens it using the private mode so the file is accessible by only your app.

Context context = getActivity();
SharedPreferences sharedPref = context.getSharedPreferences(
        getString(R.string.preference_file_key), Context.MODE_PRIVATE);

When naming your shared preference files, you should use a name that‘s uniquely identifiable to your app, such as "com.example.myapp.PREFERENCE_FILE_KEY"

Alternatively, if you need just one shared preference file for your activity, you can use the getPreferences()method:

SharedPreferences sharedPref = getActivity().getPreferences(Context.MODE_PRIVATE);

Caution: If you create a shared preferences file with MODE_WORLD_READABLE or MODE_WORLD_WRITEABLE, then any other apps that know the file identifier can access your data.

Write to Shared Preferences

To write to a shared preferences file, create a SharedPreferences.Editor by calling edit() on yourSharedPreferences.

Pass the keys and values you want to write with methods such as putInt() and putString(). Then call commit()to save the changes. For example:

SharedPreferences sharedPref = getActivity().getPreferences(Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPref.edit();
editor.putInt(getString(R.string.saved_high_score), newHighScore);
editor.commit();

Read from Shared Preferences

To retrieve values from a shared preferences file, call methods such as getInt() and getString(), providing the key for the value you want, and optionally a default value to return if the key isn‘t present. For example:

SharedPreferences sharedPref = getActivity().getPreferences(Context.MODE_PRIVATE);
int defaultValue = getResources().getInteger(R.string.saved_high_score_default);
long highScore = sharedPref.getInt(getString(R.string.saved_high_score), defaultValue);

Saving Key-Value Sets

标签：android数据存储   sharedpreference   

原文地址：http://blog.csdn.net/sweetvvck/article/details/38645065