SharedPreferences你用对了吗

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一般的使用套路

SharedPreferences sharedPreferences = context.getSharedPreferences("test", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.putString("name", "test");
editor.commit();

实际上，SharedPreferences提交更改除了commit还有一个方法apply

SharedPreferences sharedPreferences = context.getSharedPreferences("test", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.putString("name", "test");
//editor.commit();
editor.apply();

那这两者有啥区别呢？

/**
 * 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();

把注释拿出来了，大家可以看下。

我们可以总结出来这么几点区别：

1. commit和apply方法都是用来提交更改的，而且提交多次的话会以最后一次提交的为准，也就是最后一次的更改是最终的结果，这个很好理解。
2. commit方法有返回值，提交成功会返回true，失败返回false；而apply方法没有返回值。
3. commit方法是同步提交的，而apply方法是异步提交，不会阻塞当前线程。

那我们该怎么使用这2种方法呢？总结如下：

如果需要知道提交结果的返回值的话，那就只能用commit方法了，不过实际上我们很少需要知道。所以除非有必要，绝大多数情况下都推荐使用apply方法来提交更改，特别是在主线程当中。这样可以提高应用性能。

以上，希望能帮到大家。

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