Sharedpreferences – 蓝天白云

　　SharedPreferences貌似很简单的一个类，却也存在着陷阱，如下面，我们写了几行简单的保存配置的代码，但却隐含着bug

SharedPreferences prefs = getSharedPreferences("config", Context.MODE_PRIVATE);
prefs.edit().putInt("runcount", 100);
prefs.edit().apply();

SharedPreferences prefs = getSharedPreferences("config", Context.MODE_PRIVATE);

prefs.edit().putInt("runcount", 100);

prefs.edit().apply();

　　那么为什么这段代码不能保存runcount的数据呢，因为prefs.edit()每次返回一个新的Editor对象，所以执行两次prefs.edit()其实调用的是两个Editor对象，如下adnroid源码中的解释

   /**
     * 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();

/**

* 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();

　　因此，我们应该先将prefs.edit()赋值给一个Editor对象，然后由该对象进行存值和提交操作，如下：

SharedPreferences prefs = getSharedPreferences("config", Context.MODE_PRIVATE);
Editor editor = prefs.edit();
editor.putInt("runcount", 100);
editor.apply();

SharedPreferences prefs = getSharedPreferences("config", Context.MODE_PRIVATE);

Editor editor = prefs.edit();

editor.putInt("runcount", 100);

editor.apply();