应用升级期间是否清除了Android活动instanceState？

Question

In the instanceState of an activity we store a Serializable (bundle.putSerializable). In a crash report from the Play Store we saw the following stack trace:

Caused by: java.lang.ClassNotFoundException: o.ণ
at java.lang.Class.classForName(Class.java)
at java.lang.Class.forName(Class.java:308)
at android.os.Parcel$2.resolveClass(Parcel.java:2373)
at java.io.ObjectInputStream.readNewClassDesc(ObjectInputStream.java:1641)
at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:657)
at java.io.ObjectInputStream.readNewObject(ObjectInputStream.java:1782)
at java.io.ObjectInputStream.readNonPrimitiveContent(ObjectInputStream.java:761)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:1983)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:1940)
at android.os.Parcel.readSerializable(Parcel.java:2381)

Our code is obfuscated by DexGuard. It looks like Android is able to serialize the class but not able to deserialize the class.

The only reason we currently can think of is an upgrade of the app (via de Play Store). Between the version the class is changed (because of Dexguard) making a deserialization impossible.

So, my question is: does Android clean all instanceState of an app during the upgrade of an App or not?

Answer 1

As far as I know, the only condition under which the system restores the state of an Activity when it's completely destroyed is when the system had to destroy that Activity to recover system memory. In all other cases (force process to stop, reinstallation of the app, restart of the device) the state is lost.

About the reinstallation, you have to consider that when you install a new version of the app, you have probably changed or removed one or more activities, and the state of the old activities cannot probably match the state of the new ones. Suppose for example that in a single Activity app, you have a TextView with id "@+id/my_text". After few days, you decide to remove the TextView and assign the id "my_text" to another View - for example a Spinner: how could the system restore the text of the TextView in a Spinner?

Answer 2

You shouldn't include custom classes in the saved instanceState if there is any chance that those classes will change (even if it's only DexGuard shuffling names around). The system persists some information about recent activities and may try to reuse it across upgrades.