Read & writing arrays of Parcelable objects

android, parcelable

Solution

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);
}

Problem

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?

Original source