Modify Struct variable in a Dictionary

Question

I have a struct like this:

public struct MapTile
{
    public int bgAnimation;
    public int bgFrame;
}

But when I loop over it with forea

Answer 1

tilesData[tile.Key] is not a storage location (i.e., it's not a variable). It's a copy of the instance of MapTile associated with the key tile.Key in the dictionary tilesData. This is what happens with struct. Copies of their instances get passed around and returned everywhere (and is a large part of why mutable struct are considered evil).

What you need to do is:

    MapTile tile = tilesData[tile.Key];
    if (tile.bgFrame >= tile.bgAnimation)
    {
        tile.bgFrame = 0;
    }
    else
    {
        tile.bgFrame++;
    }
    tilesData[tile.Key] = tile;