What's the point of having a default value in sharedPref.getString?

Question

I\'m accessing my Android apps SharedPreferences via

private val sharedPref = PreferenceManager.getDefaultSharedPreferences(context)`
         


        

Answer 1

It's because kotlin Null-Safety is kick in when reading the following code:

val lat: String = sharedPref.getString("MyKey", "Default")

if you visit the SharedPreferences code, you can see the following code:

@Nullable
String getString(String key, @Nullable String defValue);

which is give us a probability to use null as defValue parameter. So, Kotlin try to guard it and give you the matching error:

"Type mismatch. Required String, found String?"

You can fix the problem by enabling nullable for your String variable with:

val lat: String? = sharedPref.getString("MyKey", "Default")

though this against Kotlin type system purpose:

Kotlin's type system is aimed at eliminating the danger of null references from code, also known as the The Billion Dollar Mistake.