写在前面
今天在写 LifeTips App 时，涉及到存储用户调节的屏幕亮度时，使用了 SharedPreferences，及 SharedPreferences.Editor，结果 Android Studio 出现了”黄色的感叹号“（本人有强迫症，不喜欢任何 warning。。），提示：Consider using apply() instead of commit on SharedPreferences. Whereas commit blocks and writes its data to persistent storage immediately， apply will handle it in the background. 所以就将 editor.commit(); 改为 editor.apply()了。
LifeTips App GitHub源码链接：https://github.com/selfconzrr/LifeTips
知其然就要知其所以然：看官方文档
commit()的文档
官方文档如下:
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()的文档
官方文档如下:
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.
文档说明
需要注意的是 commit() 方法是 Added in API level 1 的，也就是 sdk1 就已经存在了。而 apply() 方法是 Added in API level 9 的。
- commit() 有返回值，成功返回 true，失败返回 false。而 apply() 没有返回值。
- commit() 方法是同步提交到硬件磁盘，因此，在多个并发的提交 commit 的时候，他们会等待正在处理的 commit 保存到磁盘后在操作，从而降低了效率。
- apply() 是将修改的数据提交到内存，而后异步真正的提交到硬件磁盘。
为什么建议使用apply()替代commit() ?
因为 Android 的设计人员发现，开发人员对 commit() 的返回值不感兴趣，而且在数据并发处理时使用 commit() 要比 apply() 效率低，所以推荐使用apply()。
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