how to properly implement Parcelable with an ArrayList<Parcelable>?

Question

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?

Solution 1

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.

Solution 2

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

_devices = in.createTypedArrayList(ZigBeeDev.CREATOR);

Solution 3

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

Solution 4

In constructor you should use

_lqis = in.createTypedArrayList(ZigBeeDev.CREATOR);

And in "writeToParcel" use

out.writeTypedList(_lqis);

View more solutions

Comments

[gatlingxyz]

For future reference, and I'm not sure if it's a typo that no one has noticed, but ZigBeeDev.Creator should be ZigBeeDev.CREATOR. I got an error every time until I realized there were two different creators I could use in my own project.

[AlexAndro]

@NitroG42 The second approach for read list results into cannot convert from void to ArrayList<Integer>

[sgarman]

I also needed to instantiate the array before as well, example my code would look like: _devices = new ArrayList<ZigBeeDev>(); in.readTypedList(_devices, ZigBeeDev.Creator);

[rf43]

fwiw - the reason you were receiving a NPE is because if you use in.readTypedList() you need to create a new ArrayList() first and then pass that to the in.readTypedList(yourNewArrayList, YourObj.CREATOR) otherwise it will only be trying to put the data into a null list.

[osrl]

Yes, that's correct. I've read the source code before I used it. Thank you for the extra information which I forgot to write.

[Ajit Kumar Dubey]

@osrl when we follow your solution got exception java.lang.OutOfMemoryError: Failed to allocate a 13893804 byte allocation with 11004100 free bytes and 10MB until OOM

[osrl]

Does your array hold files or something big? @Ajit

[crubio]

@sgarman There's no need to instantiate the array cause then you get the warning: Explicit type argument ZigBeeDev can be replaced with <> This inspection reports all new expressions with type arguments which can be replaced with diamond type <>

[Eido95]

Confirm to be working with generic Hashtable that uses primitives types (including String) for either of his keys or values.