C＃Dictionary - 字典中没有给定的键

Question

I'm currently trying to load game objects from a Tiled (Tiled map editor) map file into a game engine I'm making in C#. I'm using TiledSharp (Link to github here ). It uses a dictionary to hold properties about each individual tile (or 'game object') I'm trying to load. But for some reason I get an error when I loop through the properties, and I also get an error if I check if it's null

Here's a snippet of the code I'm using:

for (int l = 0; l < tmxMap.Tilesets[k].Tiles.Count; l++)
    // This line throws an error
    if (tmxMap.Tilesets[k].Tiles[l].Properties != null)
        // and if I remove the above line, this line throws an error
        for (int m = 0; m < tmxMap.Tilesets[k].Tiles[l].Properties.Count; m++)

The error I get says The given key was not present in the dictionary. But... I'm not even checking for a key.

Am I missing something?

Any help would be appreciated.

Answer 1

The error I get says The given key was not present in the dictionary. But... I'm not even checking for a key.

Yes you are checking for a key. This is your code:

if (tmxMap.Tilesets[k].Tiles[l].Properties != null)

You are checking for Tilesets with key k and then checking Tiles with key l . If the Tilesets does not contain an item with key k , you will get that error. The same is true for Tiles with key l .

You can do the following when working with dictionaries:

Option 1

The lookup is performed twice: once to see if the item exists, and then a second time to get the value:

var items = new Dictionary<string, string>();
items.Add("OneKey", "OneValue");
if(items.ContainsKey("OneKey"))
{
    var val = items["OneKey"];
}

Option 2

And here is another approach where the lookup is performed once:

string tryVal;
if (items.TryGetValue("OneKey", out tryVal))
{
    // item with key exists so you can use the tryVal
}

Answer 2

As far as I can see in your code I think that Tiles is a Dictionary and when you try to iterate by tmxMap.Tilesets[k].Tiles[l] it throws error because it searches for key l, not for the l-element.

You can try tmxMap.Tilesets[k].Tiles[tmxMap.Tilesets[k].Tiles.Keys.ElementAt(l)]

Answer 3

You are trying to get a value based on keys k , l .

if (tmxMap.Tilesets[k].Tiles[l].Properties != null) statement is basically getting the value corresponding to the k key in Tilesets dictionary. If Tilesets dictionary doesn't contain a value for the key k , an exception will be thrown. Also if there is no value corresponding to the l key, in Tiles dictionary, exception will be thrown.

You can use TryGetValue extension method, which will give you the value if the item was found.

    TileSet ts = null;

    if(tmxMap.Tilesets.TryGetValue(k, out ts)
    {
       for (int l = 0; l < ts.Tiles.Count; l++)
       { 
          Tiles tl = null;

          if(ts.TryGetValue(l,out tl)
          {
            if (tl.Properties != null)
            {
              for (int m = 0; m < tl.Properties.Count; m++)
              {
               //Do something
              }
            }
          }
        }
     }