fire event from bool setter

Question

I'm trying to fire an event when a bool has actually changed value. I read that using a custom set and get method is one of the ways to do this. But I keep getting NullReferenceException: Object reference not set to an instance of an object

Public class Ball : MonoBehaviour {
public delegate void ballEvents();
public static event ballEvents OnBallStop;

private bool _previousValue = true;
private bool _ballStopped = true;
public bool BallHasStopped {
    get {return _ballStopped;}
    set {
        _ballStopped = value;
        if (_ballStopped != _previousValue){
            _previousValue = _ballStopped;
            if(value == true) {
                print("stop");
                OnBallStop(); // this causes the error
            } else {
                print("moving");
            }
        }           
    }
}

As a side note, you do not need to keep `_previousValue` - before you do the assignment to `_ballStopped`, you've got the previous value in `_ballStopped`, and new value in `value` - so you can just have `if (_ballStopped != value) { _ballStopped = value; doWhatever(); }` in the setter. — Luaan, Jan 16 '15 at 16:59

Servy · Accepted Answer · 2015-01-16T17:12:06.050

3

When an event has no handlers it is null, and so cannot be invoked. You can check for null and not invoke it unless there are handlers.

edited Jan 16 '15 at 17:12

answered Jan 16 '15 at 16:55

Servy

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Or he can have `Events` and Raise them. Checking is not required in events. – Nikhil Agrawal Jan 16 '15 at 17:11
1

@NikhilAgrawal Yes, there are technically a ton of alternatives; this is just one. – Servy Jan 16 '15 at 17:12

fire event from bool setter

1 Answers1