Can Delegates.observable() be serializable?

Question

Given a class

class Pizza(name: String?) : Serializable {
    var name: String? by Delegates.observable(name, {_,_,_ -> })
}

Why is this not serializable? It crashes with

Caused by: java.io.NotSerializableException: com.xxx.xxx.Pizza$$special$$inlined$observable$1

Answer 1

The reason behind your issue is the delegates are stored as an array in a synthetic backing field which is neither marked as transient nor serialziable, so it prevents the serialization. However just marking the property with @Transient will probably ruin your serialized form. _{And may not work at all}

Before JetBrains decide to make a final resolution to this issue, you should use writeReplace and readResolve to override the default serializing mechanism. I've provided a sample solution below:

class Pizza(name: String?) : Serializable {
    @Transient var name: String? by Delegates.observable(name)
    private fun writeReplace(stream: ObjectOutputStream): Object = SerialProxy(name)
    private class SerialProxy(var name: String): Serializable {
        private fun readResolve(): Object = Pizza(name)
    }
}

_{readObject()/writeObject() doesn't work because you have no way to set the delegate after constructor is invoked without using reflection.}