android/content/SharedPreferences.java

/*
 * Copyright (C) 2006 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.content;

import android.annotation.Nullable;

import java.util.Map;
import java.util.Set;

/**
 * Interface for accessing and modifying preference data returned by {@link
 * Context#getSharedPreferences}.  For any particular set of preferences,
 * there is a single instance of this class that all clients share.
 * Modifications to the preferences must go through an {@link Editor} object
 * to ensure the preference values remain in a consistent state and control
 * when they are committed to storage.  Objects that are returned from the
 * various <code>get</code> methods must be treated as immutable by the application.
 *
 * <p>Note: This class provides strong consistency guarantees. It is using expensive operations
 * which might slow down an app. Frequently changing properties or properties where loss can be
 * tolerated should use other mechanisms. For more details read the comments on
 * {@link Editor#commit()} and {@link Editor#apply()}.
 *
 * <p><em>Note: This class does not support use across multiple processes.</em>
 *
 * <div class="special reference">
 * <h3>Developer Guides</h3>
 * <p>For more information about using SharedPreferences, read the
 * <a href="{@docRoot}guide/topics/data/data-storage.html#pref">Data Storage</a>
 * developer guide.</p></div>
 *
 * @see Context#getSharedPreferences
 */
public interface SharedPreferences {
    /**
     * Interface definition for a callback to be invoked when a shared
     * preference is changed.
     */
    public interface OnSharedPreferenceChangeListener {
        /**
         * Called when a shared preference is changed, added, or removed. This
         * may be called even if a preference is set to its existing value.
         *
         * <p>This callback will be run on your main thread.
         *
         * <p><em>Note: This callback will not be triggered when preferences are cleared
         * via {@link Editor#clear()}, unless targeting {@link android.os.Build.VERSION_CODES#R}
         * on devices running OS versions {@link android.os.Build.VERSION_CODES#R Android R}
         * or later.</em>
         *
         * @param sharedPreferences The {@link SharedPreferences} that received the change.
         * @param key The key of the preference that was changed, added, or removed. Apps targeting
         *            {@link android.os.Build.VERSION_CODES#R} on devices running OS versions
         *            {@link android.os.Build.VERSION_CODES#R Android R} or later, will receive
         *            a {@code null} value when preferences are cleared.
         */
        void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key);
    }

    /**
     * Interface used for modifying values in a {@link SharedPreferences}
     * object.  All changes you make in an editor are batched, and not copied
     * back to the original {@link SharedPreferences} until you call {@link #commit}
     * or {@link #apply}
     */
    public interface Editor {
        /**
         * Set a String value in the preferences editor, to be written back once
         * {@link #commit} or {@link #apply} are called.
         * 
         * @param key The name of the preference to modify.
         * @param value The new value for the preference.  Passing {@code null}
         *    for this argument is equivalent to calling {@link #remove(String)} with
         *    this key.
         * 
         * @return Returns a reference to the same Editor object, so you can
         * chain put calls together.
         */
        Editor putString(String key, @Nullable String value);
        
        /**
         * Set a set of String values in the preferences editor, to be written
         * back once {@link #commit} or {@link #apply} is called.
         * 
         * @param key The name of the preference to modify.
         * @param values The set of new values for the preference.  Passing {@code null}
         *    for this argument is equivalent to calling {@link #remove(String)} with
         *    this key.
         * @return Returns a reference to the same Editor object, so you can
         * chain put calls together.
         */
        Editor putStringSet(String key, @Nullable Set<String> values);
        
        /**
         * Set an int value in the preferences editor, to be written back once
         * {@link #commit} or {@link #apply} are called.
         * 
         * @param key The name of the preference to modify.
         * @param value The new value for the preference.
         * 
         * @return Returns a reference to the same Editor object, so you can
         * chain put calls together.
         */
        Editor putInt(String key, int value);
        
        /**
         * Set a long value in the preferences editor, to be written back once
         * {@link #commit} or {@link #apply} are called.
         * 
         * @param key The name of the preference to modify.
         * @param value The new value for the preference.
         * 
         * @return Returns a reference to the same Editor object, so you can
         * chain put calls together.
         */
        Editor putLong(String key, long value);
        
        /**
         * Set a float value in the preferences editor, to be written back once
         * {@link #commit} or {@link #apply} are called.
         * 
         * @param key The name of the preference to modify.
         * @param value The new value for the preference.
         * 
         * @return Returns a reference to the same Editor object, so you can
         * chain put calls together.
         */
        Editor putFloat(String key, float value);
        
        /**
         * Set a boolean value in the preferences editor, to be written back
         * once {@link #commit} or {@link #apply} are called.
         * 
         * @param key The name of the preference to modify.
         * @param value The new value for the preference.
         * 
         * @return Returns a reference to the same Editor object, so you can
         * chain put calls together.
         */
        Editor putBoolean(String key, boolean value);

        /**
         * Mark in the editor that a preference value should be removed, which
         * will be done in the actual preferences once {@link #commit} is
         * called.
         * 
         * <p>Note that when committing back to the preferences, all removals
         * are done first, regardless of whether you called remove before
         * or after put methods on this editor.
         * 
         * @param key The name of the preference to remove.
         * 
         * @return Returns a reference to the same Editor object, so you can
         * chain put calls together.
         */
        Editor remove(String key);

        /**
         * Mark in the editor to remove <em>all</em> values from the
         * preferences.  Once commit is called, the only remaining preferences
         * will be any that you have defined in this editor.
         * 
         * <p>Note that when committing back to the preferences, the clear
         * is done first, regardless of whether you called clear before
         * or after put methods on this editor.
         * 
         * @return Returns a reference to the same Editor object, so you can
         * chain put calls together.
         */
        Editor clear();

        /**
         * Commit your preferences changes back from this Editor to the
         * {@link SharedPreferences} object it is editing.  This atomically
         * performs the requested modifications, replacing whatever is currently
         * in the SharedPreferences.
         *
         * <p>Note that when two editors are modifying preferences at the same
         * time, the last one to call commit wins.
         *
         * <p>If you don't care about the return value and you're
         * using this from your application's main thread, consider
         * using {@link #apply} instead.
         *
         * @return Returns true if the new values were successfully written
         * to persistent storage.
         */
        boolean commit();

        /**
         * Commit your preferences changes back from this Editor to the
         * {@link SharedPreferences} object it is editing.  This atomically
         * performs the requested modifications, replacing whatever is currently
         * in the SharedPreferences.
         *
         * <p>Note that when two editors are modifying preferences at the same
         * time, the last one to call apply wins.
         *
         * <p>Unlike {@link #commit}, which writes its preferences out
         * to persistent storage synchronously, {@link #apply}
         * commits its changes to the in-memory
         * {@link SharedPreferences} immediately but starts an
         * asynchronous commit to disk and you won't be notified of
         * any failures.  If another editor on this
         * {@link SharedPreferences} does a regular {@link #commit}
         * while a {@link #apply} is still outstanding, the
         * {@link #commit} will block until all async commits are
         * completed as well as the commit itself.
         *
         * <p>As {@link SharedPreferences} instances are singletons within
         * a process, it's safe to replace any instance of {@link #commit} with
         * {@link #apply} if you were already ignoring the return value.
         *
         * <p>You don't need to worry about Android component
         * lifecycles and their interaction with <code>apply()</code>
         * writing to disk.  The framework makes sure in-flight disk
         * writes from <code>apply()</code> complete before switching
         * states.
         *
         * <p class='note'>The SharedPreferences.Editor interface
         * isn't expected to be implemented directly.  However, if you
         * previously did implement it and are now getting errors
         * about missing <code>apply()</code>, you can simply call
         * {@link #commit} from <code>apply()</code>.
         */
        void apply();
    }

    /**
     * Retrieve all values from the preferences.
     *
     * <p>Note that you <em>must not</em> modify the collection returned
     * by this method, or alter any of its contents.  The consistency of your
     * stored data is not guaranteed if you do.
     *
     * @return Returns a map containing a list of pairs key/value representing
     * the preferences.
     *
     * @throws NullPointerException
     */
    Map<String, ?> getAll();

    /**
     * Retrieve a String value from the preferences.
     * 
     * @param key The name of the preference to retrieve.
     * @param defValue Value to return if this preference does not exist.
     * 
     * @return Returns the preference value if it exists, or defValue.  Throws
     * ClassCastException if there is a preference with this name that is not
     * a String.
     * 
     * @throws ClassCastException
     */
    @Nullable
    String getString(String key, @Nullable String defValue);
    
    /**
     * Retrieve a set of String values from the preferences.
     * 
     * <p>Note that you <em>must not</em> modify the set instance returned
     * by this call.  The consistency of the stored data is not guaranteed
     * if you do, nor is your ability to modify the instance at all.
     *
     * @param key The name of the preference to retrieve.
     * @param defValues Values to return if this preference does not exist.
     * 
     * @return Returns the preference values if they exist, or defValues.
     * Throws ClassCastException if there is a preference with this name
     * that is not a Set.
     * 
     * @throws ClassCastException
     */
    @Nullable
    Set<String> getStringSet(String key, @Nullable Set<String> defValues);
    
    /**
     * Retrieve an int value from the preferences.
     * 
     * @param key The name of the preference to retrieve.
     * @param defValue Value to return if this preference does not exist.
     * 
     * @return Returns the preference value if it exists, or defValue.  Throws
     * ClassCastException if there is a preference with this name that is not
     * an int.
     * 
     * @throws ClassCastException
     */
    int getInt(String key, int defValue);
    
    /**
     * Retrieve a long value from the preferences.
     * 
     * @param key The name of the preference to retrieve.
     * @param defValue Value to return if this preference does not exist.
     * 
     * @return Returns the preference value if it exists, or defValue.  Throws
     * ClassCastException if there is a preference with this name that is not
     * a long.
     * 
     * @throws ClassCastException
     */
    long getLong(String key, long defValue);
    
    /**
     * Retrieve a float value from the preferences.
     * 
     * @param key The name of the preference to retrieve.
     * @param defValue Value to return if this preference does not exist.
     * 
     * @return Returns the preference value if it exists, or defValue.  Throws
     * ClassCastException if there is a preference with this name that is not
     * a float.
     * 
     * @throws ClassCastException
     */
    float getFloat(String key, float defValue);
    
    /**
     * Retrieve a boolean value from the preferences.
     * 
     * @param key The name of the preference to retrieve.
     * @param defValue Value to return if this preference does not exist.
     * 
     * @return Returns the preference value if it exists, or defValue.  Throws
     * ClassCastException if there is a preference with this name that is not
     * a boolean.
     * 
     * @throws ClassCastException
     */
    boolean getBoolean(String key, boolean defValue);

    /**
     * Checks whether the preferences contains a preference.
     * 
     * @param key The name of the preference to check.
     * @return Returns true if the preference exists in the preferences,
     *         otherwise false.
     */
    boolean contains(String key);
    
    /**
     * Create a new Editor for these preferences, through which you can make
     * modifications to the data in the preferences and atomically commit those
     * changes back to the SharedPreferences object.
     * 
     * <p>Note that you <em>must</em> call {@link Editor#commit} to have any
     * changes you perform in the Editor actually show up in the
     * SharedPreferences.
     * 
     * @return Returns a new instance of the {@link Editor} interface, allowing
     * you to modify the values in this SharedPreferences object.
     */
    Editor edit();
    
    /**
     * Registers a callback to be invoked when a change happens to a preference.
     *
     * <p class="caution"><strong>Caution:</strong> The preference manager does
     * not currently store a strong reference to the listener. You must store a
     * strong reference to the listener, or it will be susceptible to garbage
     * collection. We recommend you keep a reference to the listener in the
     * instance data of an object that will exist as long as you need the
     * listener.</p>
     *
     * @param listener The callback that will run.
     * @see #unregisterOnSharedPreferenceChangeListener
     */
    void registerOnSharedPreferenceChangeListener(OnSharedPreferenceChangeListener listener);

    /**
     * Unregisters a previous callback.
     *
     * @param listener The callback that should be unregistered.
     * @see #registerOnSharedPreferenceChangeListener
     */
    void unregisterOnSharedPreferenceChangeListener(OnSharedPreferenceChangeListener listener);
}