SharedPreferences中的commit和apply方法

1. SharedPreferences对象获取
context类中的getSharedPreferences方法可以获取一个SharedPreferences对象
private File makeFilename(File base, String name) {        if (name.indexOf(File.separatorChar) < 0) {            return new File(base, name);        }        throw new IllegalArgumentException(                "File " + name + " contains a path separator");    }
其本质也是在文件不存在的情况下new一个File
2. commit方法
源码注释：
 /** * 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方法是有一个boolean的返回值
当数据变化进行存储时是一个原子性的操作
当两个editor对象同时对一个共享的preferences参数进行操作时，永远都是最后一个调用commit方法的editor变更了最后的数据值
3. apply方法
源码注释：
/*** 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();
apply方法是没有返回值的
当两个editor同时对preferences对象编辑时，也是最后一个调用apply方法的对象编辑数据
apply的提交操作也是原子性的
4. commit和apply方法的区别：
commit和apply虽然都是原子性操作，但是原子的操作不同，commit是原子提交到数据库，所以从提交数据到存在Disk中都是同步过程，中间不可打断。
而apply方法的原子操作是原子提交的内存中，而非数据库，所以在提交到内存中时不可打断，之后再异步提交数据到数据库中，因此也不会有相应的返回值。
所有commit提交是同步过程，效率会比apply异步提交的速度慢，但是apply没有返回值，永远无法知道存储是否失败。
在不关心提交结果是否成功的情况下，优先考虑apply方法。


作者：doMyselfzy
链接：http://www.jianshu.com/p/c8d10357c939
來源：简书
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