Question

I’m getting this error in C# while trying to build an importer for a tilemap. It’s supposed to read files formatted like this;

DatMapName!
6|4
SpritePageID:SpriteID:OffsetX:OffsetY|SpritePageID:SpriteID:OffsetX:OffsetY SpritePageID:SpriteID:OffsetX:OffsetY
SpritePageID:SpriteID:OffsetX:OffsetY|SpritePageID:SpriteID:OffsetX:OffsetY SpritePageID:SpriteID:OffsetX:OffsetY

into a data structure built up like this;

map
    MapTile[MapSizeX, MapSizeY]
        Tile[Sprites on tile]
        - string SpritePageID
        - int SpriteID
        - Vector2 Offset

Basically it has the map name on the first line, X/Y size on the second, and then it has SpritePageID, spriteID, offsetx, offsetY separated by :, and multiple sprites per tile separated by |. Spaces delimit the different tiles.

However, during processing I get the following error;

Error   1   Building content threw NullReferenceException: Object reference not set to an instance of an object.
at LibTilePipelineExtension.LevelProcessor.Process(String input, ContentProcessorContext context) in C:\Projects\C#\XNA1\TileWorld\LibTilePipelineExtension\LevelProcessor.cs:line 45
at Microsoft.Xna.Framework.Content.Pipeline.ContentProcessor`2.Microsoft.Xna.Framework.Content.Pipeline.IContentProcessor.Process(Object input, ContentProcessorContext context)
at Microsoft.Xna.Framework.Content.Pipeline.BuildCoordinator.BuildAssetWorker(BuildItem item)
at Microsoft.Xna.Framework.Content.Pipeline.BuildCoordinator.BuildAsset(BuildItem item)
at Microsoft.Xna.Framework.Content.Pipeline.BuildCoordinator.RunTheBuild()
at Microsoft.Xna.Framework.Content.Pipeline.Tasks.BuildContent.RemoteProxy.RunTheBuild(BuildCoordinatorSettings settings, TimestampCache timestampCache, ITaskItem[] sourceAssets, String[]& outputContent, String[]& rebuiltContent, String[]& intermediates, Dictionary`2& dependencyTimestamps, KeyValuePair`2[]& warnings)
C:\Projects\C#\XNA1\TileWorld\TileWorld\TileWorldContent\tileworldtest1.tilemap TileWorld

Here’s the code that’s throwing this error.

string[] lines = input.Split(new char[] { '\n' });
// ------
// Clear out commented lines from the array. Turn it to a list, remove indices, turn back to array.
List<string> derp1 = new List<string>(lines);
for (int derp2 = 0; derp2 < derp1.Count; derp2++) {
    if (derp1[derp2][0] == ' ' || derp1[derp2][0] == ';') {
        derp1.RemoveAt(derp2);
        derp2--;
    }
}
lines = derp1.ToArray();
// ------
int rows = Convert.ToInt32(lines[1].Split('|')[0]);
int columns = Convert.ToInt32(lines[1].Split('|')[1]);

MapTile[,] res = new MapTile[rows, columns];

for (int i0 = 2; i0 < (rows + 2); i0++) {
    string[] tiles = lines[i0].Split(' ');

    for (int i1 = 0; i1 < columns; i1++) {
        string[] tileSprites = tiles[i1].Split('|');
-->     res[i0 - 2, i1].sprites = new Tile[tileSprites.Length];   <-- Exception

        for (int i2 = 0; i2 < tileSprites.Length; i2++) {
            string[] spriteData = tileSprites[i2].Split(':');

            res[i0 - 2, i1].sprites[i2] = new Tile(spriteData[0], Convert.ToInt32(spriteData[1]), new Vector2(Convert.ToInt32(spriteData[2]), Convert.ToInt32(spriteData[3])));
        }
    }
}
return new Map(res, lines[0]);

These are the classes I use to make this tree. I removed the using statements to shorten this question.

//Map.cs
namespace LibTile {
    public class Map {
        public MapTile[,] grid { get; set; }
        public string MapName { get; set; }

        public Map(MapTile[,] value) {
            grid = value;
        }
        public Map(MapTile[,] value, string name) {
            grid = value;
            MapName = name;
        }

        public MapTile GetTile(int row, int col) {
            return grid[row, col];
        }

        public int Rows {
            get {
                return grid.GetLength(0);
            }
        }

        public int Columns {
            get {
                return grid.GetLength(1);
            }
        }
    }
}

.

//MapTile.cs
namespace LibTile {
    public class MapTile {
        public Tile[] sprites { get; set; }

        public MapTile(Tile[] value) {
            sprites = value;
        }
    }
}

.

//Tile.cs
namespace LibTile {
    public class Tile {
        public String SpritePageID;
        public int SpriteID;
        public Vector2 Offset;

        public Tile(String spid, int sid, int ox, int oy) {
            SpritePageID = spid;
            SpriteID = sid;
            Offset = new Vector2(ox,oy);
        }
        public Tile(String spid, int sid, Vector2 o) {
            SpritePageID = spid;
            SpriteID = sid;
            Offset = o;
        }
    }
}

Answer 1

You create a new array of MapTile but you never initialize the individual elements. Try this:

res[i0 - 2, i1] = new MapTile(new Tile[tileSprites.Length]);

This will create a new MapTile object in each poition of the array. Not doing this was causing your null reference exception. I would also consider changing the constructor of MapTile to be parameterless and then just set MapTile.sprites as you were doing before.