[SOLVED]Custom ContentTypeReader: existingInstance

[gotji]

Can someone explain usage of parameter ‘exisitng instance’ of this method:

public abstract class ContentTypeReader<T> : ContentTypeReader {
    protected internal abstract T Read(ContentReader input, T existingInstance);
}

I’ve several custom content readers in my project but I never use this parameter and it’s always null. I can’t find any info online(MSDN page for this method returns 404).

[nkast]

It's used to reload resources after a Device lost.
If existingInstance is not null, you must reload the asset into existingInstance instead if creating a new one.

[gotji]

So for example I have simple class:

public class TileMap {
    private Dictionary<int, TileBrush> _tileBrushes;
    public Texture2D SpriteSheet { get; }
    public ReadOnlyDictionary<int, TileBrush> TileBrushes { get;  } // TileBrush is custom content
    public TileMap(Texture2D spriteSheet, IEnumerable<TileBrush> tileBrushes) {
        this._tileBrushes = tileBrushes.ToDictionary(x => x.Id);
        this.TileBrushes = new ReadOnlyDictionary<int, TileBrush>(this._tileBrushes);
    }
}

So in case you described(Device lost) I have to load SpriteSheet and TileBrushes again? This will force public setters for all properties and collection type change.

[nkast]

AFAIK, device lost is not implemented in most platforms and existingInstance is ignored by monogame core resources (Texture/VertexBuffer/Model).

Therefore you can throw an exception for now and figure it out whenever it becomes relevant.

[gotji]

Thank you. This solves the problem