ArrayList null when building Parcel

Question

One of my classes has 3 properties ArrayList like this:

public class Product implements Parcelable{

// other properties

private ArrayList<String> categoryIds;
private ArrayList<String> categorySlugs;
private ArrayList<String> categoryNames;

public Product(){}

// getters and setters

@Override
public int describeContents() {
    return 0;
}

@Override
public void writeToParcel(Parcel dest, int flags) {
    // writing other properties
    dest.writeStringList(categoryIds); // here aren't null
    dest.writeStringList(categorySlugs);
    dest.writeStringList(categoryNames);
}

public static final Parcelable.Creator<Product> CREATOR = new Parcelable.Creator<Product>() {
    public Product createFromParcel(Parcel pc) {
        return new Product(pc);
    }
    public Product[] newArray(int size) {
        return new Product[size];
    }
};

public Product(Parcel in){

    // reading other properties, all correct

    in.readStringList(categoryIds); // from here are all null
    in.readStringList(categorySlugs);
    in.readStringList(categoryNames);
}

}

Read the comments in the Parcel constructor. Those three are null but in the function "writeToParcel" they are not null. All other properties are correct. What I'm missing here?

Thanks :)

You never instantiate the List to create an instance. You need `private ArrayList categoryIds = new ArrayList()`; The `new ArrayList()` is the crucial part, as this is where you construct the object instance. — TEK, Aug 28 '15 at 15:24
It's the first time I use an ArrayList in a parcel. So far I have also my custom class' array: ArrayList and no need to instantiate. But you're completely right, it worked, thanks!! if you post it as an answer I will accept it. — Alberto Garrido, Aug 28 '15 at 15:31

score 0 · Accepted Answer · edited May 23 '17 at 12:26

0

You never instantiate the List to create an instance.

For example, you need:

private ArrayList<String> categoryIds = new ArrayList<String>();

The new ArrayList<String>() is the crucial part, as this is where you construct the object instance.

Better yet, construct these Lists in the constructor of Product. Also consider coding to interface, too.

edited May 23 '17 at 12:26

Community

1
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answered Aug 28 '15 at 15:32

TEK

1,265
1
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score 0 · Answer 2 · answered Aug 28 '15 at 15:34

0

Use below code to read lists:

categoryIds = in.createStringArrayList()

answered Aug 28 '15 at 15:34

Abdullah

7,143
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ArrayList null when building Parcel

2 Answers2