Read & writing arrays of Parcelable objects

Question

I have following class which reads and writes an array of objects from/to a parcel:

class ClassABC extends Parcelable {
    MyClass[] mObjList;

    private void readFromParcel(Parcel in) {
        mObjList = (MyClass[]) in.readParcelableArray(
                com.myApp.MyClass.class.getClassLoader()));
    }

    public void writeToParcel(Parcel out, int arg1) {
        out.writeParcelableArray(mObjList, 0);
    }

    private ClassABC(Parcel in) {
        readFromParcel(in);
    }

    public int describeContents() {
        return 0;
    }

    public static final Parcelable.Creator<ClassABC> CREATOR =
            new Parcelable.Creator<ClassABC>() {

        public ClassABC createFromParcel(Parcel in) {
            return new ClassABC(in);
        }

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

In above code I get a ClassCastException when reading readParcelableArray:

ERROR/AndroidRuntime(5880): Caused by: java.lang.ClassCastException: [Landroid.os.Parcelable;

What is wrong in above code? While writing the object array, should I first convert the array to an ArrayList?

UPDATE:

Is it OK to convert an Object array to an ArrayList and add it to parcel? For instance, when writing:

    ArrayList<MyClass> tmpArrya = new ArrayList<MyClass>(mObjList.length);
    for (int loopIndex=0;loopIndex != mObjList.length;loopIndex++) {
        tmpArrya.add(mObjList[loopIndex]);
    }
    out.writeArray(tmpArrya.toArray());

When reading:

    final ArrayList<MyClass> tmpList = 
            in.readArrayList(com.myApp.MyClass.class.getClassLoader());
    mObjList= new MyClass[tmpList.size()];
    for (int loopIndex=0;loopIndex != tmpList.size();loopIndex++) {
        mObjList[loopIndex] = tmpList.get(loopIndex);
    }

But now I get a NullPointerException. Is above approach is correct? Why it is throwing an NPE?

Answer 1

You need to write the array using the Parcel.writeTypedArray() method and read it back with the Parcel.createTypedArray() method, like so:

MyClass[] mObjList;

public void writeToParcel(Parcel out) {
    out.writeTypedArray(mObjList, 0);
}

private void readFromParcel(Parcel in) {
    mObjList = in.createTypedArray(MyClass.CREATOR);
}

The reason why you shouldn't use the readParcelableArray()/writeParcelableArray() methods is that readParcelableArray() really creates a Parcelable[] as a result. This means you cannot cast the result of the method to MyClass[]. Instead you have to create a MyClass array of the same length as the result and copy every element from the result array to the MyClass array.

Parcelable[] parcelableArray =
        parcel.readParcelableArray(MyClass.class.getClassLoader());
MyClass[] resultArray = null;
if (parcelableArray != null) {
    resultArray = Arrays.copyOf(parcelableArray, parcelableArray.length, MyClass[].class);
}