private int _MyVal;
    [Export("MyVal")]
    public int MyVal
    {
        get { return _MyVal; }
        set
        {
            WillChangeValue("MyVal");
            this._MyVal = value;
            DidChangeValue("MyVal");
        }
    }

SettingsModel.AddObserver(this, (NSString)key, NSKeyValueObservingOptions.New, this.Handle);

public override void ObserveValue(NSString keyPath, NSObject ofObject, NSDictionary change, IntPtr context)
    {
        switch (keyPath)
        {
            case "MyValue":

            // CODE HERE THAT UPDATES AN API WITH THE VALUE
            // But this handler fires twice.


            break;
        }
    }

[Export("MyVal")]
public int MyVal { get; set }

this.SettingsModel.MyVal = 1;

MainViewController.ObserveValue
ObjCRuntime.Messaging.void_objc_msgSendSuper_IntPtr()
Foundation.NSObject.DidChangeValue(string forKey)
CameraSettingsModel.set_MyValue(int value)
AppKit.NSApplication.NSApplicationMain()
AppKit.NSApplication.Main(string[] args)
MainClass.Main(string[] args)

MainViewController.ObserveValue
AppKit.NSApplication.NSApplicationMain()
AppKit.NSApplication.Main(string[] args)
MainClass.Main(string[] args)

[Export ("automaticallyNotifiesObserversForKey:")]
    public static new bool AutomaticallyNotifiesObserversForKey (string key) => false;

    bool _checkValue;

    [Export("CheckValue")]
    public bool CheckValue
    {
        get { return _checkValue; }
        set
        {
            WillChangeValue("CheckValue");
            _checkValue = value;
            DidChangeValue("CheckValue");
        }
    }

    public override void ViewDidLoad ()
    {
        base.ViewDidLoad();

        this.AddObserver("CheckValue", NSKeyValueObservingOptions.New, o =>
        {
            Console.WriteLine($"Observer triggered for {o}");
        });

        CheckValue = false;