關於SharePreference提交數據

在android 中存儲數據時常常用SharedPreference, 而且在提交數據時一直用的是Editor的commit方法, 今天無心了看到了系統用了apply,看了方法的介紹, 原來這個方法也是能夠提交數據的.

apply方法在官方SDK說明以下：

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： 
1. apply沒有返回值而commit返回boolean代表修改是否提交成功 
2. apply是將修改數據原子提交到內存, 然後異步真正提交到硬件磁盤, 而commit是同步的提交到硬件磁盤，所以，在多個併發的提交commit的時候，他們會等待正在處理的commit保存到磁盤後在操做，從而下降了效率。而apply只是原子的提交到內容，後面有調用apply的函數的將會直接覆蓋前面的內存數據，這樣從必定程度上提升了不少效率。 
3. apply方法不會提示任何失敗的提示。 
因爲在一個進程中，sharedPreference是單實例，通常不會出現併發衝突，若是對提交的結果不關心的話，建議使用apply，固然須要確保提交成功且有後續操做的話，仍是須要用commit的。