android - How to make a class with nested objects Parcelable

Question

I'd like to make class A Parcelable.

public class A {
    public String str;
    public ArrayList<B> list;
}

This is what I've come up with so far. However it crashes with a NullPointerException. The problem are these two statements: dest.writeList(list); & in.readList(list, this.getClass().getClassLoader());. I can't figure out what to do from here :(

Class A

public class A implements Parcelable {
    public String str;
    public ArrayList<B> list;

    @Override
    public int describeContents() {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(str);
        dest.writeList(list);
    }

    private A(Parcel in) {
        str = in.readString();
        in.readList(list, this.getClass().getClassLoader());
    }

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

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

Class B

public class B implements Parcelable {
    public String str;

    @Override
    public int describeContents() {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(str);
    }

    private B(Parcel in) {
        str = in.readString();
    }

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

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

Thank you for your time.

Answer 1

I finally figured out what to type into Google :), and found this Android, How to use readTypedList method correctly in a Parcelable class?

The solution was to use read-/writeTypedList instead. I also initialize the arraylist to avoid any further NullPointerException.

Class A

public class A implements Parcelable {
    public String str;
    public ArrayList<B> list = new ArrayList<B>();

    @Override
    public int describeContents() {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(str);
        dest.writeTypedList(list);
    }

    private A(Parcel in) {
        str = in.readString();
        in.readTypedList(list, B.CREATOR);
    }

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

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

Class B

public class B implements Parcelable {
    public String str;

    @Override
    public int describeContents() {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(str);
    }

    private B(Parcel in) {
        str = in.readString();
    }

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

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