Why does this return KeyNotFoundException?

Code (CSharp):

1. Dictionary<KeyCode, Action> localDict = new Dictionary<KeyCode, Action>();
2. localDict[KeyCode.A] += () => Debug.Log("yep");

Second line fails, why?

 

You can make a delegate and just add listeners to it.

But this is a dictionary retrieval problem: you can't make a delegate by asking for something that isn't IN the dictionary.

So first add a System.Action to the dictionary if the key doesn't exist.

 

Your code is short for this:

Code (CSharp):

1. Action existingAction = localDict[KeyCode.A];
2. existingAction += () => Debug.Log("yep");

You get the exception because There is no entry for KeyCode.A in the dictionary yet.

 

How do I create/add Action within Dictionary?

Code (CSharp):

1. Dictionary<KeyCode, Action> localDict = new Dictionary<KeyCode, Action>();
2. if (localDict.TryGetValue(KeyCode.A, out var p)) p += () => Debug.Log("yep");
3. else
4. {
5.    p = new Action(); // what?
6.    p += () => Debug.Log("yep");
7. }

 

Code (CSharp):

1. Dictionary<KeyCode, Action> localDict = new Dictionary<KeyCode, Action>();
2. Action toAdd = () => Debug.Log("yep");
3. if (localDict.TryGetValue(KeyCode.A, out var p)) {
4.    p += toAdd;
5. }
6. else {
7.    localDict[KeyCode.A] = toAdd;
8. }

Edit: This code is actually incorrect. See below in the thread for more information

 

Thank you.

 

Given https://forum.unity.com/threads/method-assigned-to-delegate-doesnt-run.1035496/#post-6704575 you might actually need to do this... not 100% sure.

Code (CSharp):

1. Dictionary<KeyCode, Action> localDict = new Dictionary<KeyCode, Action>();
2. Action toAdd = () => Debug.Log("yep");
3. if (localDict.TryGetValue(KeyCode.A, out var p)) {
4.    p += toAdd;
5.    toAdd = p;
6. }
7.  
8. localDict[KeyCode.A] = toAdd;
9.  

 

Small edit to this code. p+=toAdd will not modify action in dictionary because delegates are immutable and this code modify only local p variable. to modify record in dictionary you should use code like this

Code (CSharp):

1. Dictionary<KeyCode, Action> localDict = new Dictionary<KeyCode, Action>();
2. Action toAdd = () => Debug.Log("yep");
3. if (localDict.TryGetValue(KeyCode.A, out var p)) {
4.    p += toAdd;
5. }
6. else
7. {
8.     p = toAdd;
9. }
10. localDict[KeyCode.A] = p;
11. }

 

Hey Volod, thanks a lot for this clarification (here and in the other thread)... I didn't understand this fundamental nature and now that you explain it, it makes complete sense with all past observations.