Android(安卓)SharedPreference源码浅析

一、SharedPreference简单使用

**
问题：
1.如果两个activity都使用同一个sharedpreference，但是第一个activity没有提交，第二个activity提交了，那么会出现什么结果。

2.不同的进程是否可以共享同一个sharedpreference

mode:
Context.MODE_PRIVATE:只被本地程序读写
Context.MODE_WORLD_READABLE:能被其他程序读
Context:MODE_WORLD_WRITEABLE:能被其他程序读、写

SPActivity:

Button mButtonStorage = (Button) findViewById(R.id.btn_storage);mButtonStorage.setOnClickListener(v -> {SharedPreferences sp = getPreferences(MODE_PRIVATE); //这是Activity特有的方法，只是当前activity使用，其他的activity使用不了Log.i(TAG,sp.getString("key","123"));SharedPreferences.Editor edit = sp.edit();edit.putString("key","key");Log.i(TAG,sp.getString("key","123"));Intent intent = new Intent(SPActivity.this, SPTargetActivity.class);startActivity(intent);});

SPTargetActivity:

Button mButtonStorage = (Button) findViewById(R.id.btn_storage);mButtonStorage.setOnClickListener(v -> {SharedPreferences sp = getPreferences(MODE_PRIVATE);SharedPreferences.Editor edit = sp.edit();edit.putString("key","value");edit.apply();Log.i(TAG,sp.getString("key","123"));});

结果
显示从SP到SPTarget，然后返回SP过程中的结果

结果说明：两个Activity不是在同一个Sharedpreference文件进行操作

SPActivity:

Button mButtonStorage = (Button) findViewById(R.id.btn_storage);mButtonStorage.setOnClickListener(v -> {// SharedPreferences sp = getPreferences(MODE_PRIVATE);SharedPreferences sp1 = getSharedPreferences("123",MODE_PRIVATE);//获取应用目录下的sp，应用内可以共享Log.i(TAG,sp1.getString("key","123"));SharedPreferences.Editor edit = sp1.edit();edit.putString("key","key");Log.i(TAG,sp1.getString("key","123"));Intent intent = new Intent(SPActivity.this, SPTargetActivity.class);startActivity(intent);});

SPTargetActivity:

Button mButtonStorage = (Button) findViewById(R.id.btn_storage);mButtonStorage.setOnClickListener(v -> {// SharedPreferences sp = getPreferences("",MODE_PRIVATE);SharedPreferences sp1 = getSharedPreferences("123",MODE_PRIVATE);SharedPreferences.Editor edit = sp1.edit();edit.putString("key","value");edit.apply();Log.i(TAG,sp1.getString("key","123"));});

结果
显示从SP到SPTarget，然后返回SP过程中的结果

结果说明：两个activity处理的是同一个文件，而且后一个Editor才是有效果的，SPActivity中的Editor并没有起作用，数据没有提交。

二、源码解析：

/**  #通过 Context.getSharedPreference(),获取对象。在所有客户端中，Sharedpreference是单例的。  #修改Sharedpreference必须通过提供的Editor接口，确保value值持久化存储。  #获取数据通过get()方法获取。* #Note: 不能用于多线程中.** <div class="special reference">* 
Developer Guides
* For more information about using SharedPreferences, read the* "{@docRoot}guide/topics/data/data-storage.html#pref">Data Storage* developer guide.
div>** @see Context#getSharedPreferences*/public interface SharedPreferences {    /**     * Interface definition for a callback to be invoked when a shared     * preference is changed.        回调接口监听器     */    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.         *         * This callback will be run on your main thread.         *         * @param sharedPreferences The {@link SharedPreferences} that received         *            the change.         * @param key The key of the preference that was changed, added, or         *            removed.         */        void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key);    }    /**     #用于修改Sharedpreference中的值。但是所有的修改的值，必须在调用方法commit 或者 apply方法之后才能成功修改     */    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 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.         #标记key对应的记录应该被删除，但是必须在commit执行之后才能删除数据         *         * 
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.         #当执行commit方法，提交的时候，所有之前标记删除的操作都会先执行，无论是在put存数据之前还是之后是否执行了。也就是说，删除操作都会先执行，和删除的代码在哪里没关系。         *         * @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 all values from the         * preferences.  Once commit is called, the only remaining preferences         * will be any that you have defined in this editor.         #在editor标记中，删除所有数据。一旦提交，剩下的首选项将是您在这个编辑器中定义的任何参数         *         * 
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.       #和删除操作一样，清空操作都会先执行         *         * @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.         #从Editor中提交变化到正在修改的Sharedpreference中。这是自动执行的修改，无论是否在当前的Sharedpreference中，都会进行替换         *         * 
Note that when two editors are modifying preferences at the same         * time, the last one to call commit wins.         #当两个Editor同时修改preference的时候，后一个执行的才有效         *         * 
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.         #如果不关心返回值，而且是在主线程中操作的，可以考虑使用apply方法         *         * @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.        # 从Editor中提交变化到正在修改的Sharedpreference中。这是自动执行的修改，无论是否在当前的Sharedpreference中，都会进行替换         *         * 
Note that when two editors are modifying preferences at the same         * time, the last one to call apply wins.         *         * 
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.         #不像commit方法，它同步的写preferences到持久化存储。apply提交变化值到内存中，Sharedpreference立即开启一个异步提交到磁盘中，而且你不会收到任何失败的信息。如果同时另一个editor调用commit方法，这是将会先执行apply方法，commit()将会被阻塞，知道所有的异步提交完成，以及提交自身。         *         * 
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.         #在一个进程中，Sharedpreference是单例的，如果你已经不关注返回值了，使用apply替换commit就是安全的         *         * 
You don't need to worry about Android component         * lifecycles and their interaction with apply()         * writing to disk.  The framework makes sure in-flight disk         * writes from apply() complete before switching         * states.         #你不需要担心android组件风格和他们的相互作用，当使用apply写到磁盘存储的时候。框架确保在转变状态之前，运转的磁盘能够从apply()方法完成写操作。         *         * 
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 apply(), you can simply call         * {@link #commit} from apply().         #SharedPreferences.Editor接口是不希望直接实现的。然而，如果你之前已经实现了，并且现在正在获取有关缺少apply()方法的错误，则你只需要从apply()调用commit即可。         */        void apply();    }    /**     * Retrieve all values from the preferences.      #从preference中取回所有键值对     * 
Note that you must not 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.     #禁止改变返回的集合，或者修改内容。如果你做了，保存数据的一致性也不会被保证。     *     * @return Returns a map containing a list of pairs key/value representing     * the preferences.     *     * @throws NullPointerException     */    Map getAll();    /**     * Retrieve a String value from the preferences.     #根据key获取对应的String类型的value值     * @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.     #从preference中取回String类型值的集合     * 
Note that you must not 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 getStringSet(String key, @Nullable Set 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.     #判断是否包含key     * @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.     *     * 
Note that you must 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.     #注册一个回调函数，当preference被改变的时候，能够被调用     * 
class="caution">Caution: 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.
     *     * @param listener The callback that will run.     * @see #unregisterOnSharedPreferenceChangeListener     */    void registerOnSharedPreferenceChangeListener(OnSharedPreferenceChangeListener listener);    /**     * Unregisters a previous callback.     #取消注册之前的回调函数     * @param listener The callback that should be unregistered.     * @see #registerOnSharedPreferenceChangeListener     */    void unregisterOnSharedPreferenceChangeListener(OnSharedPreferenceChangeListener listener);}

Context.java中调用Sharedpreference方法的方法：

/*** Retrieve and hold the contents of the preferences file 'name', returning* a SharedPreferences through which you can retrieve and modify its* values.  Only one instance of the SharedPreferences object is returned* to any callers for the same name, meaning they will see each other's* edits as soon as they are made.#取回并且持有文件名为name的preferences内容，返回Sharedpreference，然后你可以取回和修改内容。Sharedpreference仅有一个实例能够被返回给任何调用者。意味着，一旦某个使用者作出改变，其他人都能看见他的编辑。* @param name Desired preferences file. If a preferences file by this name* does not exist, it will be created when you retrieve an* editor (SharedPreferences.edit()) and then commit changes (Editor.commit()).* @param mode Operating mode.** @return The single {@link SharedPreferences} instance that can be used*         to retrieve and modify the preference values.** @see #MODE_PRIVATE*/public abstract SharedPreferences getSharedPreferences(String name, @PreferencesMode int mode);/*** Retrieve and hold the contents of the preferences file, returning* a SharedPreferences through which you can retrieve and modify its* values.  Only one instance of the SharedPreferences object is returned* to any callers for the same name, meaning they will see each other's* edits as soon as they are made.** @param file Desired preferences file. If a preferences file by this name* does not exist, it will be created when you retrieve an* editor (SharedPreferences.edit()) and then commit changes (Editor.commit()).* @param mode Operating mode.** @return The single {@link SharedPreferences} instance that can be used*         to retrieve and modify the preference values.** @see #getSharedPreferencesPath(String)* @see #MODE_PRIVATE* @removed*/public abstract SharedPreferences getSharedPreferences(File file, @PreferencesMode int mode);/*** Move an existing shared preferences file from the given source storage* context to this context. This is typically used to migrate data between* storage locations after an upgrade, such as moving to device protected* storage.** @param sourceContext The source context which contains the existing*            shared preferences to move.* @param name The name of the shared preferences file.* @return {@code true} if the move was successful or if the shared*         preferences didn't exist in the source context, otherwise*         {@code false}.* @see #createDeviceProtectedStorageContext()*/public abstract boolean moveSharedPreferencesFrom(Context sourceContext, String name);/*** Delete an existing shared preferences file.** @param name The name (unique in the application package) of the shared*            preferences file.* @return {@code true} if the shared preferences file was successfully*         deleted; else {@code false}.* @see #getSharedPreferences(String, int)*/public abstract boolean deleteSharedPreferences(String name);/*** Returns the absolute path on the filesystem where a file created with* {@link #getSharedPreferences(String, int)} is stored.* * The returned path may change over time if the calling app is moved to an* adopted storage device, so only relative paths should be persisted.** @param name The name of the shared preferences for which you would like*            to get a path.* @return An absolute path to the given file.* @see #getSharedPreferences(String, int)* @removed*/public abstract File getSharedPreferencesPath(String name);

一、SharedPreference简单使用

二、源码解析：

Developer Guides

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