Android SharedPreferences String Set - some items are removed after app restart

Question

I save a string set in the shared preferences, if I read it out it\'s ok. I start other activities, go back and read it again, it\'s ok. If I close the application, and start it

Answer 1

This "problem" is documented on SharedPreferences.getStringSet().

getStringSet() returns a reference of the stored HashSet object inside SharedPreferences. When you add elements to this object, they are added in fact inside SharedPreferences.

The workaround is making a copy of the returned Set and putting the new Set into SharedPreferences. I tested it and it works.

In Kotlin, that would be

    val setFromSharedPreferences = sharedPreferences.getStringSet("key", mutableSetOf())
    val copyOfSet = setFromSharedPreferences.toMutableSet()
    copyOfSet.add(addedString)

    val editor = sharedPreferences.edit()
    editor.putStringSet("key", copyOfSet)
    editor.apply() // or commit() if really needed