Can Nulls be passed to parcel?

Question

Is it possible to write null to Parcel when parcelling an object, and get null back again when unparcelling it again?

Let's assume we have the following code:

public class Test implements Parcelable {
    private String string = null;
    public Test(Parcel dest, int flags) {
        source.writeString(string);
    }
}

Will I get a NullPointerException when reading this value back from the parcel using Parcel.readString()?

Or will I get a null value out?

score 17 · Accepted Answer · edited May 23 '17 at 12:34

17

Yes, you can pass a null to the Parcel.writeString(String) method.

When you read it out again with Parcel.readString(), you will get a null value out.

For example, assume you have a class with the following fields in it:

public class Test implements Parcelable {
    public final int id;
    private final String name;
    public final String description;
    ...

You create the Parcelable implementation like this (using Android Studio autoparcelable tool):

@Override
public void writeToParcel(Parcel dest, int flags) {
    dest.writeInt(id);
    dest.writeString(null); // NOTE the null value here
    dest.writeString(description);
}

protected Test(Parcel in) {
    id = in.readInt();
    name = in.readString();
    description = in.readString();
}

When running this code, and passing a Test object as a Parcelable extra in an Intent, 2 points become apparent:

the code runs perfectly without any NullPointerException
the deserialised Test object has a value name == null

You can see similar info in the comments to this related question:

Parcel, ClassLoader and Reading Null values

edited May 23 '17 at 12:34

Community

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1

answered Dec 19 '15 at 12:15

Richard Le Mesurier

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1

This is exactly the behaviour I expected! Thank you for the corrections. – Fattum Dec 19 '15 at 15:10
I'm having apparent problems serializing Double values (that can be null) - when reading from the Parcel with readDouble() i get a double (primitive) back, and that fails, with "Attempt to invoke virtual method 'double java.lang.Double.doubleValue()' on a null object reference" – tplive Jul 06 '18 at 07:35
Yes, `getDouble()` returns a primitive double that would have to have been added with `setDouble()` which also takes a primitive double. I imagine if you try that with a null `Double` object you would run into problems. – Richard Le Mesurier Jul 06 '18 at 09:17
I have a List of custom class right after a string that can be null. If I call writeString() as normal as you show above, I get the nasty unmarshalling unknown type error for the next List during deserialization of Parcelable. If I use empty string if it is null, then it works perfectly. – Mehmed Oct 22 '18 at 10:03
@Mehmed you should probably post that as a new question with full details. I recommend linking to this question and answer, explaining the differences in detail so it does not get closed as a duplicate (which would be likely otherwise). – Richard Le Mesurier Oct 22 '18 at 12:05

score 1 · Answer 2 · answered Aug 27 '19 at 02:41

If you want to write other data types such as Integer, Double, Boolean with possible null values to a parcel, you can use Parcel.writeSerializable().

When reading these values back from parcel, you have to cast the value returned by Parcel.readSerializable() to the correct data type.

Double myDouble = null;
dest.writeSerializable(myDouble);  // Write

Double readValue = (Double) dest.readSerializable();   // Read

score 0 · Answer 3 · answered Sep 22 '17 at 17:08

0

In my case (Kotlin)

 override fun writeToParcel(parcel: Parcel, flags: Int) {
        parcel.writeInt(if (PapperId == null) -1 else PapperId)
        parcel.writeString( if (Nome == null) "" else Nome)
}

answered Sep 22 '17 at 17:08

FlipNovid

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Imo using default values must be used only after a case analysis. If we'd use your method to store a Integer price, then without value it would default to 0, i can buy it, a lot of it !! Really, no value is different than default value. – Mostrapotski Jul 05 '19 at 07:08

Can Nulls be passed to parcel?

3 Answers3

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