Question

In Windows Phone 7 -> IsolatedStorageSettings class we have two functions Add() and Save(). According to me both are doing the same thing meanings saving a key value pair in Isolated Storage. My question what is the difference between these two functions.

To test this what is did was in App.xaml.cs in Application_Deactivated event and Application_Closing event I added one key value pair in IsolatedStorageSettings without calling the save function.

On Application_Launched and Application_Activated event I am retrieving same key value pair and I am getting same value for the key which I had added above.

So, without actually calling Save function of IsolatedStorageSettings I am able to retrieve the values.

Answer 1

.Save() actually persists the isolated storage settings instance (such as ApplicationSettings) to the media (e.g. phone storage).

This is automatically done when your application is tombestoned (_Deactivated) or closed (_Closed). That is why you get same value without even calling save.

.Add() method just adds a new entry to your dictionary of settings. This change may be missed if your settings is not saved (usually when app is exited unexpectedly).

From MSDN:

“Data written to the IsolatedStorageSettings object is saved when the
application that uses the class is closed. This can occur when the
user closes the Web browser, refreshes a page, or browses away from
the page. If you want your application to write to isolated storage
immediately, you can call the Save method in application code.”

Hope this answers your question