SharedPreferences.Editor 的apply()與commit()方法的區別

commit()的文檔

官方文檔如下:

Commit your preferences changes back from this Editor to the SharedPreferences object it is editing. This atomically performs the requested modifications, replacing whatever is currently in the SharedPreferences.

Note that when two editors are modifying preferences at the same time, the last one to call commit wins.

If you don't care about the return value and you're using this from your application's main thread, consider using apply() instead.

apply()的文檔

官方文檔如下:

Commit your preferences changes back from this Editor to the SharedPreferences object it is editing. This atomically performs the requested modifications, replacing whatever is currently in the SharedPreferences.

Note that when two editors are modifying preferences at the same time, the last one to call apply wins.

Unlike commit(), which writes its preferences out to persistent storage synchronously, apply() commits its changes to the in-memory SharedPreferences immediately but starts an asynchronous commit to disk and you won't be notified of any failures. If another editor on this SharedPreferences does a regular commit() while a apply() is still outstanding, the commit() will block until all async commits are completed as well as the commit itself.

As SharedPreferences instances are singletons within a process, it's safe to replace any instance of commit() with apply() if you were already ignoring the return value.

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.

解釋說明

1. 需要注意的是commit()方法是Added in API level 1的,也就是sdk1就已經存在了.

2. apply()方法是Added in API level 9的.

3. commit()有返回值,成功返回true,失敗返回false.commit()方法是同步提交到硬件磁盤，因此，在多個并發的提交commit的時候，他們會等待正在處理的commit保存到磁盤后在操作，從而降低了效率。

4. apply()沒有返回值.apply()是將修改的數據提交到內存, 而后異步真正的提交到硬件磁盤.

為什么建議使用apply()替代commit() ?

答:因為Android的設計人員發現,開發人員對commit的返回值不感興趣,而且在數據并發處理時使用commit要比apply效率低,所以推薦使用apply.