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); } 

Answer 2

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

According to the API, readParcelableArray method returns Parcelable array (Parcelable[]), which can not be simply casted to MyClass array (MyClass[]).

But now i get Null Pointer Exception.

It is hard to tell the exact cause without the detailed exception stack trace.

---

Suppose you have made MyClass implements Parcelable properly, this is how we usually do for serialize/deserialize a array of parcelable objects:

public class ClassABC implements Parcelable {    private List<MyClass> mObjList; // MyClass should implement Parcelable properly    // ==================== Parcelable ====================   public int describeContents() {     return 0;   }    public void writeToParcel(Parcel out, int flags) {     out.writeList(mObjList);   }    private ClassABC(Parcel in) {     mObjList = new ArrayList<MyClass>();     in.readList(mObjList, getClass().getClassLoader());    }    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];     }   };  } 

Hope this helps.

You can also use the following methods:

  public void writeToParcel(Parcel out, int flags) {       out.writeTypedList(mObjList);   }    private ClassABC(Parcel in) {       mObjList = new ArrayList<ClassABC>();       in.readTypedList(mObjList, ClassABC.CREATOR);   }