1 page.title=Saving Key-Value Sets 2 page.tags=data storage 3 helpoutsWidget=true 4 5 trainingnavtop=true 6 7 @jd:body 8 9 10 <div id="tb-wrapper"> 11 <div id="tb"> 12 13 <h2>This lesson teaches you to</h2> 14 <ol> 15 <li><a href="#GetSharedPreferences">Get a Handle to a SharedPreferences</a></li> 16 <li><a href="#WriteSharedPreference">Write to Shared Preferences</a></li> 17 <li><a href="#ReadSharedPreference">Read from Shared Preferences</a></li> 18 </ol> 19 20 <h2>You should also read</h2> 21 <ul> 22 <li><a href="{@docRoot}guide/topics/data/data-storage.html#pref">Using Shared Preferences</a></li> 23 </ul> 24 25 </div> 26 </div> 27 28 29 <p>If you have a relatively small collection of key-values that you'd like to save, 30 you should use the {@link android.content.SharedPreferences} APIs. 31 A {@link android.content.SharedPreferences} object points to a file containing 32 key-value pairs and provides simple methods to read and write them. Each 33 {@link android.content.SharedPreferences} file is 34 managed by the framework and can be private or shared.</p> 35 36 <p>This class shows you how to use the {@link android.content.SharedPreferences} APIs to store and 37 retrieve simple values.</p> 38 39 <p class="note"><strong>Note:</strong> The {@link android.content.SharedPreferences} APIs are 40 only for reading and writing key-value pairs and you should not confuse them with the 41 {@link android.preference.Preference} APIs, which help you build a user interface 42 for your app settings (although they use {@link android.content.SharedPreferences} as their 43 implementation to save the app settings). For information about using the {@link 44 android.preference.Preference} APIs, see the <a href="{@docRoot}guide/topics/ui/settings.html" 45 >Settings</a> guide.</p> 46 47 <h2 id="GetSharedPreferences">Get a Handle to a SharedPreferences</h2> 48 49 <p>You can create a new shared preference file or access an existing 50 one by calling one of two methods:</p> 51 <ul> 52 <li>{@link android.content.Context#getSharedPreferences(String,int) 53 getSharedPreferences()} — Use this if you need multiple shared preference files identified 54 by name, which you specify with the first parameter. You can call this from any 55 {@link android.content.Context} in your app.</li> 56 <li>{@link android.app.Activity#getPreferences(int) getPreferences()} — Use this from an 57 {@link android.app.Activity} if you need 58 to use only one shared preference file for the activity. Because this retrieves a default shared 59 preference file that belongs to the activity, you don't need to supply a name.</li> 60 </ul> 61 62 <p>For example, the following code is executed inside a {@link android.app.Fragment}. 63 It accesses the shared preferences file that's 64 identified by the resource string {@code R.string.preference_file_key} and opens it using 65 the private mode so the file is accessible by only your app.</p> 66 67 <pre> 68 Context context = getActivity(); 69 SharedPreferences sharedPref = context.getSharedPreferences( 70 getString(R.string.preference_file_key), Context.MODE_PRIVATE); 71 </pre> 72 73 <p>When naming your shared preference files, you should use a name that's uniquely identifiable 74 to your app, such as {@code "com.example.myapp.PREFERENCE_FILE_KEY"}</p> 75 76 <p>Alternatively, if you need just one shared preference file for your activity, you can use the 77 {@link android.app.Activity#getPreferences(int) getPreferences()} method:</p> 78 79 <pre> 80 SharedPreferences sharedPref = getActivity().getPreferences(Context.MODE_PRIVATE); 81 </pre> 82 83 <p class="caution"><strong>Caution:</strong> If you create a shared preferences file 84 with {@link android.content.Context#MODE_WORLD_READABLE} or {@link 85 android.content.Context#MODE_WORLD_WRITEABLE}, then any other apps that know the file identifier 86 can access your data.</p> 87 88 89 <h2 id="WriteSharedPreference">Write to Shared Preferences</h2> 90 91 <p>To write to a shared preferences file, create a {@link 92 android.content.SharedPreferences.Editor} by calling {@link 93 android.content.SharedPreferences#edit} on your {@link android.content.SharedPreferences}.</p> 94 95 <p>Pass the keys and values you want to write with methods such as {@link 96 android.content.SharedPreferences.Editor#putInt putInt()} and {@link 97 android.content.SharedPreferences.Editor#putString putString()}. Then call {@link 98 android.content.SharedPreferences.Editor#commit} to save the changes. For example:</p> 99 100 <pre> 101 SharedPreferences sharedPref = getActivity().getPreferences(Context.MODE_PRIVATE); 102 SharedPreferences.Editor editor = sharedPref.edit(); 103 editor.putInt(getString(R.string.saved_high_score), newHighScore); 104 editor.commit(); 105 </pre> 106 107 108 <h2 id="ReadSharedPreference">Read from Shared Preferences</h2> 109 110 <p>To retrieve values from a shared preferences file, call methods such as {@link 111 android.content.SharedPreferences#getInt getInt()} and {@link 112 android.content.SharedPreferences#getString getString()}, providing the key for the value 113 you want, and optionally a default value to return if the key isn't 114 present. For example:</p> 115 116 <pre> 117 SharedPreferences sharedPref = getActivity().getPreferences(Context.MODE_PRIVATE); 118 int defaultValue = getResources().getInteger(R.string.saved_high_score_default); 119 long highScore = sharedPref.getInt(getString(R.string.saved_high_score), defaultValue); 120 </pre> 121 122
