C＃中的KeyNotFoundException

Question

I got an Exception here that doesn't find the rootPartNo key in unbreakableLinkMap dictionary.

MyTree<IDbRecord> currentTree = PartHelper.GetTreeForRootId(succesorId, graph);
#region TreeSheet
string rootPartNo = currentTree.Root.Payload.GetField(Part.c_partNo).GetString();

//get spirit links
var spiritLinks = graph.unbreakableLinkMap[rootPartNo];
Worksheet treeWS = excel.Worksheets[2];
treeWS.Name = "Tree";
long displayedPartId = long.Parse(GetIdFromSession(Part.t_name));
int rowNo = 0;
bool bold = false;
Color color = Color.Black;
foreach (MyTreeNode<IDbRecord> node in currentTree.Root.DepthFirstNodeEnumerator)
{
    string partNo = node.Payload.GetField(Part.c_partNo).GetString();
    treeWS.Cells[rowNo, node.Depth].PutValue(partNo);
    bold = false;
    color = Color.Black;
    if (spiritLinks.Find(suc => suc.PartNo == partNo || suc.SucPartNo == partNo) != null)
    {
        color = Color.Red;
    }
    if (node.Payload.GetField(Part.c_id).GetInt64() == displayedPartId)
    {
        bold = true;
    }

    headerFStyle.Font.IsBold = bold;
    headerFStyle.Font.Color = color;
    treeWS.Cells[rowNo, node.Depth].SetStyle(headerFStyle);
    rowNo++;
}

How can I check/validate this?

Answer 1

Usually you get this exception when the key specified for accessing an element in a collection does not match any key in the collection.

I would suggest use the debugger and see you have that Key available in the Dictionary

If you are unsure of key existence, I would suggest writing defensive code, using ContainsKey or TryGetValue .

if (graph.unbreakableLinkMap.ContainsKey(key)) 
{
     ... 
}

or

if (graph.unbreakableLinkMap.TryGetValue(key, out spiritLinks)) {}

Answer 2

Well, you have to debug. Put a breakpoint on the

  var spiritLinks = graph.unbreakableLinkMap[rootPartNo];

line, run the routine and inspect the values of question:

  rootPartNo

as well as dictionary keys

  graph.unbreakableLinkMap.Keys

If you can't use debugger for whatever reason, add debug output

  ...
  string rootPartNo = currentTree.Root.Payload.GetField(Part.c_partNo).GetString();

  // Debug output: when key is not found, show additional info
  if (!graph.unbreakableLinkMap.ContainsKey[rootPartNo])
    MessageBox.Show(String.Format(
      "Key to find is \"{0}\" and keys in the dictionary are\r\n{1}", 
      rootPartNo, 
      String.Join(", ", graph.unbreakableLinkMap.Keys)));

  ...