Null pointer error when passing Parcelable data

Question

I am trying to pass an Order Object between two activities. This object contains an ArrayList of MenuItems. The class for Order is below: (it implements the parcelable interface).

public class Order extends ArrayList <MenuItem> implements Parcelable {

private int covers;
private int table;
//To hold MenuItems
private ArrayList<MenuItem> items;

public Order(){

}

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

    @Override
    public Order createFromParcel(Parcel source) {
        return new Order(source);
    }

    @Override
    public Order[] newArray(int size) {
        return new Order[size];
    }


};

public Order(int covers, int table, ArrayList<MenuItem> items) {
    super();
    this.covers = covers;
    this.table = table;
    this.items = items;
}

public int getCovers() {
    return covers;
}

public void setCovers(int covers) {
    this.covers = covers;
}

public int getTable() {
    return table;
}

public void setTable(int table) {
    this.table = table;
}

public ArrayList<MenuItem> getItems() {
    return items;
}

public void setItems(ArrayList<MenuItem> items) {
    this.items = items;
}

//add menu item to order
public void addToOrder(MenuItem m){
    items.add(m);
}

//remove menu item from order
public void removeFromOrder(MenuItem m){
    items.remove(m);
}


public Order(Parcel source) {
    readFromParcel(source);

}

private void readFromParcel(Parcel source) {

    this.clear();

    //read the size of the list
    int size = source.readInt();

    //Remember order of items written into the Parcel. Important here.
    for(int i = 0; i < size; i ++){
        MenuItem item = new MenuItem();
        item.setName(source.readString());
        item.setPrice(source.readDouble());
        this.add(item);
}

}

@Override
public void writeToParcel(Parcel dest, int arg1) {
        int size = this.size();

                dest.writeInt(size);

                for(int i = 0; i < size; i ++){
                    MenuItem item = this.get(i);
                    dest.writeString(item.getName());
                    dest.writeDouble(item.getPrice());

                }

            }

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

}

When my activity starts I create a new order item and place it in an Intent to be sent to the next activity. When I click the button to start the new activity I get the following error:

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.waitron5/com.example.waitron5.SectionsActivity}: java.lang.NullPointerException

Below is my code I use in MainActivity.java to place the object into the Intent.

//Order object to hold details about order for duration of session
Order order;
ArrayList<Order> orderList;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    //As soon as app is started up create an order object.
    order = new Order();
    orderList = new ArrayList<Order>();
    orderList.add(order);

    //reference to button and add listeners
    orderBtn = (Button)findViewById(R.id.orderBtn);
    orderBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            //Create a new intent and start up the sections activity...
            i = new Intent(v.getContext(), SectionsActivity.class);
            i.putExtra("data", (ArrayList<Order>)orderList);
            startActivity(i);
        }
    });

}

Below is my code I use in SectionsActivity.java to retrieve my object from the Intent.

//Get order information
public void getOrderData(){
    i = getIntent();
    if(i != null && i.hasExtra("data")){
        Toast.makeText(this.getApplicationContext(), "recieved", Toast.LENGTH_SHORT).show();
        order = i.getParcelableExtra("data");
        int size = order.size();
        Toast.makeText(this.getApplicationContext(), String.valueOf(size), Toast.LENGTH_SHORT).show();
    }
}

Does anyone know why I am getting this error. I know it's because It can't find the parcelable object, I just don't know how I should go about fixing it! Many thanks.

EDIT: I think problem lies somewhere within this chunk of code:

@Override
public void writeToParcel(Parcel dest, int flags) {
        int size = this.size();
                dest.writeInt(size);
                for(int i = 0; i < size; i ++){
                    MenuItem item = this.get(i);
                    dest.writeString(item.getName());
                    dest.writeDouble(item.getPrice());

                }

            }

LOG CAT ERRORS

01-09 23:41:23.706: E/AndroidRuntime(22717): FATAL EXCEPTION: main 01-09 23:41:23.706: E/AndroidRuntime(22717): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.waitron5/com.example.waitron5.SectionsActivity}: java.lang.NullPointerException 01-09 23:41:23.706: E/AndroidRuntime(22717): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180) 01-09 23:41:23.706: E/AndroidRuntime(22717): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 01-09 23:41:23.706: E/AndroidRuntime(22717): at android.app.ActivityThread.access$600(ActivityThread.java:141) 01-09 23:41:23.706: E/AndroidRuntime(22717): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 01-09 23:41:23.706: E/AndroidRuntime(22717): at android.os.Handler.dispatchMessage(Handler.java:99) 01-09 23:41:23.706: E/AndroidRuntime(22717): at android.os.Looper.loop(Looper.java:137) 01-09 23:41:23.706: E/AndroidRuntime(22717): at android.app.ActivityThread.main(ActivityThread.java:5039) 01-09 23:41:23.706: E/AndroidRuntime(22717): at java.lang.reflect.Method.invokeNative(Native Method) 01-09 23:41:23.706: E/AndroidRuntime(22717): at java.lang.reflect.Method.invoke(Method.java:511) 01-09 23:41:23.706: E/AndroidRuntime(22717): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 01-09 23:41:23.706: E/AndroidRuntime(22717): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 01-09 23:41:23.706: E/AndroidRuntime(22717): at dalvik.system.NativeStart.main(Native Method) 01-09 23:41:23.706: E/AndroidRuntime(22717): Caused by: java.lang.NullPointerException 01-09 23:41:23.706: E/AndroidRuntime(22717): at com.example.waitron5.SectionsActivity.getOrderData(SectionsActivity.java:113) 01-09 23:41:23.706: E/AndroidRuntime(22717): at com.example.waitron5.SectionsActivity.onCreate(SectionsActivity.java:44) 01-09 23:41:23.706: E/AndroidRuntime(22717): at android.app.Activity.performCreate(Activity.java:5104) 01-09 23:41:23.706: E/AndroidRuntime(22717): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080) 01-09 23:41:23.706: E/AndroidRuntime(22717): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144) 01-09 23:41:23.706: E/AndroidRuntime(22717): ... 11 more

LOG CAT WARNING

*01-09 23:41:23.676: W/Bundle(22717): Key data expected Parcelable but value was a java.util.ArrayList. The default value was returned. 01-09 23:41:23.686: W/Bundle(22717): Attempt to cast generated internal exception: 01-09 23:41:23.686: W/Bundle(22717): java.lang.ClassCastException: java.util.ArrayList cannot be cast to android.os.Parcelable 01-09 23:41:23.686: W/Bundle(22717): at android.os.Bundle.getParcelable(Bundle.java:1171) 01-09 23:41:23.686: W/Bundle(22717): at android.content.Intent.getParcelableExtra(Intent.java:4330) 01-09 23:41:23.686: W/Bundle(22717): at com.example.waitron5.SectionsActivity.getOrderData(SectionsActivity.java:112) 01-09 23:41:23.686: W/Bundle(22717): at com.example.waitron5.SectionsActivity.onCreate(SectionsActivity.java:44) *

Answer 1

I managed to resolve my problem. The issue was that the Order class was implementing Parcelable as it should. However because it contained a list of MenuItems the MenuItem class was also required to implement the Parcelable interface.

Once I did this the problem was fixed.

Answer 2

Change i = getIntent();

by

i = getIntent().getCharSequenceArrayListExtra("data");

Update to get ArrayList

Answer 3

It would be very helpful to see the full LogCat stack trace to know exactly where the error occurs, but I can see one potential problem right away.

Your default constructor doesn't call the super constructor:

public Order(){

}

So when writeToParcel() is called you try to fetch values from what is probably a null list.

MenuItem item = this.get(i); // You never initialized the super class...