SharedPreferences - Android Key-Value键值存储

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写SudaLogin Android app时，使用了SharedPreferences来实现保存配置信息等Key-Value形式的数据。

SharedPreferences - Android Key-Value键值存储

1 SharedPreferences

  • SharedPreferences 适用于存储小型数据，如配置信息，设置项。

1.1 依赖包

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import android.content.Context;
import android.content.SharedPreferences;

1.2 读取示例

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// 获得SharedPreferences对象
SharedPreferences preferences = MainActivity.this.getSharedPreferences("SudaLoginDev", Context.MODE_PRIVATE);

// SharedPreferences支持Java的基本数据类型
// 参数1为key，参数2为默认返回的value（如找不到存储的键值）
preferences.getInt("frequency", 0);
prefenences.getString("username", "");
preferences.getBoolean("enable", true);

1.3 写入示例

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// 获得SharedPreferences对象
SharedPreferences preferences = MainActivity.this.getSharedPreferences("SudaLoginDev", Context.MODE_PRIVATE);
// 获得编辑器对象
SharedPreferences.Editor editor = preferences.edit();

// SharedPreferences支持Java的基本数据类型
// 参数1为key，参数2为对应的value
editor.putInt("frequency", 1);
editor.putString("username", "name1");
editor.putBoolean("enable", true);

// 写入编辑结束后，须提交
// editor.commit();	
editor.apply();		// 优化：apply自动优化写入时机，性能比占用同步资源的commit更好
  • 我编写的时候，发现网上的资料大多老旧，还在使用editor.commit()。Android官方现推荐调用editor.apply()，以求达到更好的 IO 性能。
  • 欣赏下Android的文档 - commit()， apply()方法的Declaration
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/**
 * 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();
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/**
 * 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();
  • 阅读即知，apply()是异步（asynchronous）写入，会根据修改情况，自动优化写入时机，以减少IO访问次数，实现更好的IO性能。而commit()则是同步写入（synchronous），特别是应用主线程中，为减少同步等待，使用apply()方法更好。

1.4 其它

另外还有如editor.remove()， editor.clear()等API，具体使用时查看Declaration即可。Android的Declaration部分代码及注释编写非常详实规范，在此赞叹一番。