Implementing Parcelable for a custom 2D array

Question

In order to pass my 2D array in a new activity, I came up with the approach to wrap it and implement the Parcelable interface. Unfortunately, when I use Intent.getParcelableExtra i get java.lang.NullPointerException, which means that I am most certainly not implementing the interface right. Below is my Updated code

public class MazeMapParcelable implements Parcelable
{
private Cell[][] mazeMap;

public MazeMapParcelable(Cell[][] mazeMap)
{
    this.mazeMap = mazeMap;
}

public Cell[][] getMazeMap()
{
    return this.mazeMap;
}


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

    public MazeMapParcelable[] newArray(int size)
    {
        return new MazeMapParcelable[size];
    }
};

public void writeToParcel(Parcel dest, int flags)
{
    int width = mazeMap.length;
    dest.writeInt(width);
    int height = mazeMap[1].length;
    dest.writeInt(height);

    for(int i=0;i<width;i++)
    {
        for(int j=0;j<height;j++)
        {
            dest.writeInt(mazeMap[i][j].getCordX());
            dest.writeInt(mazeMap[i][j].getCordY());
            dest.writeByte((byte) (mazeMap[i][j].getNorthWall() ? 1 : 0));
            dest.writeByte((byte) (mazeMap[i][j].getSouthWall() ? 1 : 0));
            dest.writeByte((byte) (mazeMap[i][j].getEastWall() ? 1 : 0));
            dest.writeByte((byte) (mazeMap[i][j].getWestWall() ? 1 : 0));
        }
    }
}

public int describeContents()
{
    return 0;
}

public MazeMapParcelable[] newArray(int size)
{
    return new MazeMapParcelable[size];
}

private MazeMapParcelable(Parcel in)
{
    int width = in.readInt();
    int height = in.readInt();
    Cell[][] recreatedMazeMap = new Cell[width][height];

    for(int i=0;i<width;i++)
    {
        for(int j=0;j<height;j++)
        {
            int cordX = in.readInt();
            int cordY = in.readInt();
            boolean northWall = in.readByte() != 0;
            boolean southWall = in.readByte() != 0;
            boolean westWall = in.readByte() != 0;
            boolean eastWall = in.readByte() != 0;
            Cell currCell = new Cell(cordX,cordY,northWall,southWall,westWall,eastWall);
            recreatedMazeMap[i][j] = currCell;
        }
    }
    mazeMap = recreatedMazeMap;
}

Note that my Cell class members are:

protected int x;
protected int y;

private boolean northWall;
private boolean southWall;
private boolean westWall;
private boolean eastWall;
private boolean bomb;
private boolean deadEnd;

Update I no longer get Null pointer exception, but my data are not written properly as they should. (parceableMazeMap[0][0] != originalMazeMap[0][0])

Answer 1

Perhaps you want to look into using writeTypedArray(). If you implement Parcelable in your Cell object, you can use writeTypedArray() to save them to the Parcel.

---

When the parcelable is attempting to recreate your instance, it calls this constructor:

private MazeMapParcelable(Parcel in){
    ...
}

But you've never actually initialized your array at this point. So it will still be in this state (which is null):

private Cell[][] mazeMap;

Since mazeMap at this state is not initialized, it will have no length. So this code will not give you the values you expect:

int width = this.mazeMap.length;
int height = this.mazeMap[1].length;

Try writing the width & height values as the first items in the parcelable, and then reading them when you're recreating the parcelable.