how to properly implement Parcelable with an ArrayList?

I am having trouble making my class Parcelable. The trouble is, I am trying to write to the parcel a member in the class which is an ArrayList<Parcelable> object. The ArrayList is Serializable, and the objects (ZigBeeDev) in the list are Parcelable.

Here is the relevant code:

package com.gnychis.coexisyst;

import java.util.ArrayList;
import java.util.Iterator;

import android.os.Parcel;
import android.os.Parcelable;

public class ZigBeeNetwork implements Parcelable {

    public String _mac;             // the source address (of the coordinator?)
    public String _pan;             // the network address
    public int _band;               // the channel
    ArrayList<Integer> _lqis;       // link quality indicators (to all devices?)
    ArrayList<ZigBeeDev> _devices;  // the devices in the network

    public void writeToParcel(Parcel out, int flags) {
        out.writeString(_mac);
        out.writeString(_pan);
        out.writeInt(_band);
        out.writeSerializable(_lqis);
        out.writeParcelable(_devices, 0);  // help here
    }

    private ZigBeeNetwork(Parcel in) {
        _mac = in.readString();
        _pan = in.readString();
        _band = in.readInt();
        _lqis = (ArrayList<Integer>) in.readSerializable();
        _devices = in.readParcelable(ZigBeeDev.class.getClassLoader());  // help here
    }

    public int describeContents() {
        return this.hashCode();
    }

    public static final Parcelable.Creator<ZigBeeNetwork> CREATOR = 
            new Parcelable.Creator<ZigBeeNetwork>() {
        public ZigBeeNetwork createFromParcel(Parcel in) {
            return new ZigBeeNetwork(in);
        }

        public ZigBeeNetwork[] newArray(int size) {
            return new ZigBeeNetwork[size];
        }
    };

    //...
}

I have marked two spots "// help here" to understand how to properly write to the parcel and how to reconstruct it. If ZigBeeDev is Parcelable (properly tested), how do I do this properly?

NitroG42

You almost got it !

You just need to do :

public void writeToParcel(Parcel out, int flags) {
    out.writeString(_mac);
    out.writeString(_pan);
    out.writeInt(_band);
    out.writeSerializable(_lqis);
    out.writeTypedList(_devices);
}

private ZigBeeNetwork(Parcel in) {
    _mac = in.readString();
    _pan = in.readString();
    _band = in.readInt();
    _lqis = (ArrayList<Integer>) in.readSerializable();
    in.readTypedList(_devices, ZigBeeDev.CREATOR);
}

That's all!

For your list of Integer, you can also do :

out.writeList(_lqis);
_lqis = new ArrayList<>();
in.readList(_lqis Integer.class.getClassLoader());

It should work.

In my case in.readTypedList(_devices, ZigBeeDev.CREATOR); gave me a NullPointerException on _devices. So I used this:

_devices = in.createTypedArrayList(ZigBeeDev.CREATOR);

You should use writeList(List l) for your list of integers and writeTypedList(List val) for the list of ZigBeeDevices

In constructor you should use

_lqis = in.createTypedArrayList(ZigBeeDev.CREATOR);

And in "writeToParcel" use

out.writeTypedList(_lqis);

A little late but I also had this issue. After a long waste of time I stumbled upon the parcelabler.com website which automatically creates parcels for you.

It allowed me to create a nested parcel with an array list inside very easily, and saved me a lot of time.

Basically the way the website works is you enter your object with the ArrayList in it and it automatically adds the necessary methods to make it parcelable (read from parcel, write to parcel, describe contents, and parcel Creator are all generated automatically). This is particularily useful when creating complex parcels, such as the question here asks, which contain nested parcels, arrays, and lists.

EDIT: Also IntelliJ IDEA and Android Studio have plugins for this which do a similar thing to the website listed: