如何将抽象对象保存到共享首选项 Android

Question

I want to save abstract object to shared preferences.I get data with String from Shared preferences and when bind it to an Abstract class, I get some errors like that "Caused by: java.lang.InstantiationException: Can't instantiate abstract class"

How to get abstract object from shared preferences?

Thanks

Answer 1

First of all, you cannot create an intance from an abstract class in java. You need to make something like this

public MyRealClass extends MyAbstractClass{

}

Your IDE should now tell you that you need to implement the needed methods from the abstract class.

You can now save the instance of MyRealClass to the SharedPreferences but only if you make it serializable or make the object to a JSON String. This can be done using libraries like GSON . It is not possible to save an object to the SharedPrefs directly.

GSON will take your instance and transforms it into a string. This string can be saved and later if you need the object again you can give the string to GSON and it will transform it back into the object. The used representation is called JSON, which is a standard format ( https://en.wikipedia.org/wiki/JSON )

To save

Gson gson = new Gson();
String json = gson.toJson(myRealClassInstance);
prefsEditor.putString("myobj", json);
prefsEditor.commit();

for later loading

Gson gson = new Gson();
String json = mPrefs.getString("myobj", "");
MyRealClass obj = gson.fromJson(json, MyRealClass.class);

Answer 2

For your Error: You can't create object of abstract class, you have to inherit abstract class to some class then only you can make an object to it.

Another one is, You can't store the object in shared preference. You can only store String, Integer, Boolean, Float, Long, and StringSet.

More info here. https://developer.android.com/reference/android/content/SharedPreferences.html