C# NullReferenceException while EventHandler

Question

I get a NullRefernceException even though I subscribed to the event in an Start Methode.

Where I create my Event:

public EventHandler<CustomArgs> ClickEvent; private void OnMouseDown() { Debug.Log("Clicked"); CustomArgs args = new CustomArgs(); args.Name = gebäude.ToString(); args.Level = Level; args.MenuePosition = Menue; ClickEvent?.Invoke(this, args); }

Where I subscribe to my Event:

private void Start() { miene.ClickEvent += ClickEvent; Debug.Log("Event Addedet"); } private void ClickEvent(object sender, CustomArgs e) { //some useless stuff }

Does this answer your question? What is a NullReferenceException, and how do I fix it? — Pavel Anikhouski
– Pavel Anikhouski, Commented May 3, 2020 at 20:34

Marc Gravell · Accepted Answer · 2020-05-03 20:13:30Z

1

Events are null when no-one has subscribed. Fortunately, modern C# makes this easy:

ClickEvent?.Invoke(this, args);

With older language versions, you need to be more verbose:

var handler = ClickEvent; if (handler != null) handler(this, args);

They mean exactly the same thing.

As a small optimisation, you may wish to defer creating the CustomArgs object until you know someone cares, though:

ClickEvent?.Invoke(this, new CustomArgs { Name = gebäude.ToString(), Level = Level, MenuePosition = Menue });

answered May 3, 2020 at 20:13

Marc Gravell

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5 Comments

Manubown Over a year ago

Yes, this is fixing the error, but not the problem. I need this Invoke because I want to do something when I get the mouse down

Marc Gravell Over a year ago

@Manubown if it is throwing an exception, then you haven't subscribed to the event. So: subscribe to the event!

Manubown Over a year ago

miene.ClickEvent += (s, args) => { //some useless stuff }; Isn't that a subscribe

Marc Gravell Over a year ago

@Manubown yes, but if the event is still null: you haven't done that - or maybe not on the right target object

Manubown Over a year ago

i have writen the subscribe command in the Update method and the OnMouseDown is a button click so I thing the Update method will be done bevor the button click.

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