java.lang.RuntimeException: Parcel android.os.Parcel: Unmarshalling unknown type code

Question

I seem to be getting a strange error in my app (see GitHub), which occurs when I pass objects to different activities that implement Parcelable.

I have checked other questions and answers here on Stack Overflow, but I was unable to find a solution. I've tried the answer here, for example - here it is for reference:

-keepclassmembers class * implements android.os.Parcelable {
    static ** CREATOR;
}

I've also made sure that the method calls in writeToParcel are in order. Most other questions on Stack Overflow about this issue don't have answers.

Moreover, the reason I am asking a new question is because I think my problem is caused because of how I have used interfaces in my app (I will expand on this point later on). Other questions on Stack Overflow would not suit my particular scenario.

In the following, I have provided links to the code via GitHub, so that you can explore more of the code if required.

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When I click on a button to launch a new activity (passing an object that implements Parcelable), there is a crash:

Process: com.satsuware.flashcards, PID: 4664
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.satsuware.flashcards/com.satsumasoftware.flashcards.ui.FlashCardActivity}: java.lang.RuntimeException: Parcel android.os.Parcel@d2219e4: Unmarshalling unknown type code 6815860 at offset 200
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
    ...
 Caused by: java.lang.RuntimeException: Parcel android.os.Parcel@d2219e4: Unmarshalling unknown type code 6815860 at offset 200
at android.os.Parcel.readValue(Parcel.java:2319)
at android.os.Parcel.readListInternal(Parcel.java:2633)
at android.os.Parcel.readArrayList(Parcel.java:1914)
at android.os.Parcel.readValue(Parcel.java:2264)
at android.os.Parcel.readArrayMapInternal(Parcel.java:2592)
at android.os.BaseBundle.unparcel(BaseBundle.java:221)
at android.os.Bundle.getParcelable(Bundle.java:786)
at android.content.Intent.getParcelableExtra(Intent.java:5377)
at com.satsumasoftware.flashcards.ui.FlashCardActivity.onCreate(FlashCardActivity.java:71)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
...

I call the aforementioned activity like so (also see GitHub):

Intent intent = new Intent(TopicDetailActivity.this, FlashCardActivity.class);
intent.putExtra(FlashCardActivity.EXTRA_TOPIC, mTopic);
intent.putExtra(FlashCardActivity.EXTRA_NUM_CARDS, mSelectedNumCards);
intent.putExtra(FlashCardActivity.EXTRA_CARD_LIST, mFilteredCards);
startActivity(intent);

The main part to consider is when I pass mTopic. This is a Topic interface that I created.

However, the Topic interface extends Parcelable and so the objects that implement Topic also include the constructor, CREATOR field, and the methods that a class implementing Parcelable would normally have to have.

You can view the relevant classes via the GitHub links, but I will provide the relevant parts of these classes below. Here is the Topic interface:

public interface Topic extends Parcelable {

    int getId();

    String getIdentifier();

    String getName();

    Course getCourse();


    ArrayList<FlashCard> getFlashCards(Context context);


    class FlashCardsRetriever {

        public static ArrayList<FlashCard> filterStandardCards(ArrayList<FlashCard> flashCards, @StandardFlashCard.ContentType int contentType) {
            ArrayList<FlashCard> filteredCards = new ArrayList<>();
            for (FlashCard flashCard : flashCards) {
                boolean isPaper2 = ((StandardFlashCard) flashCard).isPaper2();
                boolean condition;
                switch (contentType) {
                    case StandardFlashCard.PAPER_1:
                        condition = !isPaper2;
                        break;
                    case StandardFlashCard.PAPER_2:
                        condition = isPaper2;
                        break;
                    case StandardFlashCard.ALL:
                        condition = true;
                        break;
                    default:
                        throw new IllegalArgumentException("content type '" + contentType + "' is invalid");
                }
                if (condition) filteredCards.add(flashCard);
            }
            return filteredCards;
        }

        ...
    }

}

A class (object) that implements Topic:

public class CourseTopic implements Topic {

    ...

    public CourseTopic(int id, String identifier, String name, Course course) {
        ...
    }

    @Override
    public int getId() {
        return mId;
    }

    @Override
    public String getIdentifier() {
        return mIdentifier;
    }

    ...


    protected CourseTopic(Parcel in) {
        mId = in.readInt();
        mIdentifier = in.readString();
        mName = in.readString();
        mCourse = in.readParcelable(Course.class.getClassLoader());
    }

    public static final Parcelable.Creator<CourseTopic> CREATOR = new Parcelable.Creator<CourseTopic>() {
        @Override
        public CourseTopic createFromParcel(Parcel in) {
            return new CourseTopic(in);
        }

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

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

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeInt(mId);
        dest.writeString(mIdentifier);
        dest.writeString(mName);
        dest.writeParcelable(mCourse, flags);
    }

}

In one of the last lines of the code above, you can see I pass mCourse, which is a Course object I created. Here it is:

public class Course implements Parcelable {

    ...

    public Course(String subject, String examBoard, @FlashCard.CourseType String courseType,
              String revisionGuide) {
        ...
    }


    public String getSubjectIdentifier() {
        return mSubjectIdentifier;
    }

    public String getExamBoardIdentifier() {
        return mBoardIdentifier;
    }

    public ArrayList<Topic> getTopics(Context context) {
        ArrayList<Topic> topics = new ArrayList<>();
        String filename = mSubjectIdentifier + "_" + mBoardIdentifier + "_topics.csv";
        CsvParser parser = CsvUtils.getMyParser();
        try {
            List<String[]> allRows = parser.parseAll(context.getAssets().open(filename));
            for (String[] line : allRows) {
                int id = Integer.parseInt(line[0]);
                topics.add(new CourseTopic(id, line[1], line[2], this));
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return topics;
    }

    ...


    protected Course(Parcel in) {
        mSubjectIdentifier = in.readString();
        mBoardIdentifier = in.readString();
        mCourseType = in.readString();
        mRevisionGuide = in.readString();
    }

    public static final Creator<Course> CREATOR = new Creator<Course>() {
        @Override
        public Course createFromParcel(Parcel in) {
            return new Course(in);
        }

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

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

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(mSubjectIdentifier);
        dest.writeString(mBoardIdentifier);
        dest.writeString(mCourseType);
        dest.writeString(mRevisionGuide);
    }

}

I suspect something here may be causing the problem, and is the reason my scenario is different from those in other questions.

---

To be honest, I'm not exactly sure what may be causing the error, so explanations and guidance in answers would be much appreciated.

---

Edit:

After David Wasser's suggestions, I have updated parts of my code like so:

FlashCardActivity.java - onCreate(...):

Bundle extras = getIntent().getExtras();
extras.setClassLoader(Topic.class.getClassLoader());
mTopic = extras.getParcelable(EXTRA_TOPIC);

Course.java - writeToParcel(...):

dest.writeString(mSubjectIdentifier);
dest.writeString(mBoardIdentifier);
dest.writeString(mCourseType);
dest.writeInt(mRevisionGuide == null ? 0 : 1);
if (mRevisionGuide != null) dest.writeString(mRevisionGuide);

Course.java - Course(Parcel in):

mSubjectIdentifier = in.readString();
mBoardIdentifier = in.readString();
mCourseType = in.readString();
if (in.readInt() != 0) mRevisionGuide = in.readString();

I've added log messages using Log.d(...) to see if any variables are null when being passed in writeToParcel(...) and used David Wasser's method to properly handle this.

I still get the same error message, however.

Answer 1

Your problem is in LanguagesFlashCard. Here are your parcel/unparcel methods:

protected LanguagesFlashCard(Parcel in) {
    mId = in.readInt();
    mEnglish = in.readString();
    mAnswerPrefix = in.readString();
    mAnswer = in.readString();
    mTier = in.readInt();
    mTopic = in.readParcelable(Topic.class.getClassLoader());
}

As you can see, they don't match. The second item you write to the Parcel is an int, the second item you read from the Parcel is a String.

@Override
public void writeToParcel(Parcel dest, int flags) {
    dest.writeInt(mId);
    dest.writeInt(mTier);
    dest.writeString(mEnglish);
    dest.writeString(mAnswerPrefix);
    dest.writeString(mAnswer);
    dest.writeParcelable(mTopic, flags);
}