如何将Stack保存到SharedPreferences？

Question

In my Android app I have a custom stack for Strings which extends Stack . I would like to save the stack to Sharedpreferences and also retrieve it from SharedPreferences.

I know how to convert a stack to an ArrayList but I've read that SharedPreferences only supports sets not lists. So how can I save a stack to SP while preserving its order? And how can I retrieve it from SharedPreferences and rebuild the stack?

I'm really lost as to how to approach this. Any pointers in the right direction are highly appreciated - I'm not asking for code dump answers.

Answer 1

Here is one possible solution,

You can convert stack to string via serialization and save the string to shared preference

ByteArrayOutputStream bos = new ByteArrayOutputStream()
ObjectOutputStream oos = new ObjectOutputStream(bos);
oos.writeObject(stack);
oos.flush();
String base64str = Base64.encode(bos.toByteArray(), Base64.DEFAULT);
...

When load string from preference, decode the base64 string to bytes and using ObjectInputStream to deserialize the stack.

Answer 2

As per earlier comment:

You will probably have to serialize/deserialize your Stack to a string representation, which can then be stored in the SharedPreferences .

It might be possible to (ab)use the json format for this, but it does not give any guarantees about the ordering of the individual elements in the result. It should be easy enough to include the 'position' for every element too though, which you can then use to sort the elements after deserializing.

Alternatively, you can come up with your own structure.