如何将包含可包裹类“ B”的实例的可包裹类“ A”的实例写入类“ B”的包裹

Question

I have some problems with using parcelables for my Android app.
I have a custom class named Transport , which contains a bunch of RoutePoint -instances which has been loaded from a file and saved in an array.

Both the classes implements Parcelable , because I want to pass the Transport object, which contains RoutePoint objects, between multiple activities.

This brings a problem, because inside of each RoutePoint object, I have a Transport object used to tell which transport is the parent for the RoutePoint .

Pretend that I have these classes:

Transport :

public class Transport implements Parcelable
{
    private RoutePoint[] points;

    public Transport()
    {
        // Here the array is initialized
    }

    // Methods needed because of the Parcelable interface
}

RoutePoint :

public class RoutePoint implements Parcelable
{
    private Transport parent;

    public RoutePoint(Transport parent)
    {
        this.parent = parent;
    }

    // Methods needed because of the Parcelable interface
}

When the Transport class is written to a Parcel , I write all the RoutePoint s from the array to the parcel too.

When the RoutePoint class is written to a Parcel , I write the parent Transport to the parcel too.

This causes a "recursive call", and a StackOverflowException :

1. The Transport writes a RoutePoint to the Parcel .
2. The RoutePoint writes the parent Transport to the Parcel .
3. The parent Transport writes a RoutePoint to the Parcel .
4. Back to step 2.

---

I wonder how I can get around this problem, and pass the Transport class between activities, and passing the parent object in the RoutePoint class in some way.

Answer 1

If all RoutePoint instances are always contained inside a Transport instance, you can fix it by not serializing RoutePoint.parent, but rather setting it when you deserialize Transport.

So, when you deserialize a Transport instance, deserialize the RoutePoints, then call a setTransport method on those RoutePoint instances and set the parent.

Answer 2

Having Circular reference like that is not really a good idea from GC perspective too. I would suggest you have one way reference and use other data structure like BiMap etc to have those relationship defined. One way is to create an Empty constructor in RoutePoint and only parcel other item except for the parent. In Transport, while reading from parcel, set its reference later. Hope this makes sense.