Android: Parcelable returns nothing

Question

I have the following problem: I want to parcel one object from one activity to the other.

It is this object:

public class Item implements Parcelable {

private int minimumAmountOfItems;
private String nameOfItem;
private int maximumAmountOfItems;
private int actualAmountOfItems;

public Item(int minimumAmountOfItems, String nameOfItem, int     maximumAmountOfItems, int actualAmountOfItems){
    this.minimumAmountOfItems = minimumAmountOfItems;
    this.nameOfItem = nameOfItem;
    this.maximumAmountOfItems = maximumAmountOfItems;
    this.actualAmountOfItems = actualAmountOfItems;
}

With the following parcelable coding stuff:

 @Override
public int describeContents() {
    /*Necessary for the parcelable stuff; but not needed in about 99.9% of the cases (source: Stack Overflow)*/
    return 0;
}

@Override
public void writeToParcel(Parcel dest, int flags) {
    /*Store the data in a parcelable object to communicate between Activities */
    dest.writeInt(this.minimumAmountOfItems);
    dest.writeString(this.nameOfItem);
    dest.writeInt(this.maximumAmountOfItems);
    dest.writeInt(this.actualAmountOfItems);

}

private Item(Parcel in){

    /*Retrieve the data that was packaged before*/

    this.minimumAmountOfItems = in.readInt();
    this.nameOfItem = in.readString();
    this.maximumAmountOfItems = in.readInt();
    this.actualAmountOfItems = in.readInt();
}

public static final Parcelable.Creator<Item> CREATOR = new Parcelable.Creator<Item>(){
    /*This small part of code passes along the unmarshalled parcel and returns the next object.*/
    @Override
    public Item createFromParcel(Parcel in){
        return new Item(in);
    }

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

Therefore, I use in my to activities the following code to parcel my object:

resultIntent = new Intent(ItemCreatorActivity.this, ItemListEditorActivity.class);
resultIntent.putExtra("Item", item);
startActivity(resultIntent);

And to get everything I want to implement this:

Intent inputIntent = getIntent();
   Item passedItem = inputIntent.getExtras().getParcelable("Item");
System.out.println(passedItem.getNameOfItem());

Now I have several problems:

1.) How can I check, whether I get valid parcelable information from my sender to my receiver? I think that I have got everything important about parcelable objects from this tutorial: https://coderwall.com/p/vfbing/passing-objects-between-activities-in-android several others (due to readability purposes I won't post them here, because they all describe the same procedure and structure...); but still my System.out.println(passedItem.getNameOfItem()) throws nothing. And there are no further messages in my AndroidMonitor.

2.)I am calling this activity one time, when I do not have created an Item object. Is there a more "smooth" way to prevent a nullpointerexception in this code for the very first call of the activity?

3.) When I am pressing on a button, switching to a new Activity, creating an Item object and imagine, my code would have worked before and I could pass my object back to the calling Activity. Will all objects, that I have saved before in an ArrayList from the calling Activity, still be available or do I have to pass my ArrayList to the new Activity and then back to the calling Activity?

Thank you for your help in advance.

Best regards

Answer 1

You are adding parcelable object in intent and retrieving it from Bundle (inputIntent.getExtras() returns object of type Bundle).

So you need to change it to inputIntent.getParcelableExtra("Item");

3.) When I am pressing on a button, switching to a new Activity, creating an Item object and imagine, my code would have worked before and I could pass my object back to the calling Activity. Will all objects, that I have saved before in an ArrayList from the calling Activity, still be available or do I have to pass my ArrayList to the new Activity and then back to the calling Activity?

Yes. You can add ArrayList to intent object:

ArrayList<Item> itemList = new ArrayList<Item>();
// Add elements to the list
intent.putParcelableArrayListExtra("Item_List", itemList);

And retrieve it:

ArrayList<Item> itemList = inputIntent.getParcelableArrayListExtra("Item_List");

Answer 2

1.) How can I check, whether I get valid parcelable information from my sender to my receiver? I think that I have got everything important about parcelable objects from this tutorial: https://coderwall.com/p/vfbing/passing-objects-between-activities-in-android several others (due to readability purposes I won't post them here, because they all describe the same procedure and structure...); but still my System.out.println(passedItem.getNameOfItem()) throws nothing. And there are no further messages in my AndroidMonitor.

You can log to your logcat by doing

Log.d("tag", passedItem.getNameOfItem()); 

and view your logcat. It should print out your data

2.)I am calling this activity one time, when I do not have created an Item object. Is there a more "smooth" way to prevent a nullpointerexception in this code for the very first call of the activity?

You can do this in your receiving activity:

Bundle extras = getIntent().getExtras();
if (extras != null) {
   Item passedItem = (Item) extras.getParcelable("Item"); 
}

3.) When I am pressing on a button, switching to a new Activity, creating an Item object and imagine, my code would have worked before and I could pass my object back to the calling Activity. Will all objects, that I have saved before in an ArrayList from the calling Activity, still be available or do I have to pass my ArrayList to the new Activity and then back to the calling Activity?

As for this, I would look into http://developer.android.com/training/basics/activity-lifecycle/recreating.html that will teach you about recreating activities and saving data through states.