1. apply方法在 官方SDK說明 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.
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 apply(), you can simply call commit() from apply().
這兩個方法的區別在於：
apply沒有返回值而commit返回boolean表明修改是否提交成功apply是將修改數據原子提交到內存, 而後異步真正提交到硬件磁盤，後面有調用apply的函數的將會直接覆蓋前面的內存數據，這樣從一定程度上提高了很多效率commit是同步的提交到硬件磁盤，因此，在多個併發的提交commit的時候，他們會等待正在處理的commit保存到磁盤後在操作，從而降低了效率
SO 高票答案
- apply() was added in 2.3, it commits without returning a boolean indicating success or failure.
- commit() returns true if the save works, false otherwise.
- apply() was added as the Android dev team noticed that almost no one took notice of the return value, so apply is faster as it is asynchronous.