xamarin - I'm using Inotify property change.... How does INotifyPropertyChanged work? how to use it?

Question

I don't think this was covered in any tutorial that I've read or done. does any know how is this line works? This is a sample code on how to use sfnumerictextbox, but its default property is object. I need it in double or integer so Inotify came but this line is i don't get. viewModel.Numeric = numericBox.Value == null ? null : (double?)(numericBox.Value); so numeric is equal to null, so what the question mark for? then after question mark is that like if null double perhaps?

And please touch base with Inotifypropertychange.

using System;
using System.ComponentModel;
using Xamarin.Forms;

namespace NumericTextBoxSample
{
// Learn more about making custom code visible in the Xamarin.Forms previewer
// by visiting https://aka.ms/xamarinforms-previewer
[DesignTimeVisible(false)]
public partial class MainPage : ContentPage
{
    public MainPage()
    {
        InitializeComponent();
    }

    private void Button_Clicked(object sender, EventArgs e)
    {
        **viewModel.Numeric = numericBox.Value == null ? null : (double?)(numericBox.Value);**

    }
}

public class ViewModel: INotifyPropertyChanged
{
    private double? numeric;  //checkrain

    public double? Numeric //rain
    {
        get { return numeric; }
        set
        {
            numeric = value;
            RaisePropertyChanged("Numeric");
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    void RaisePropertyChanged(string property)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(property));
        }
    }

}
}

Answer 1

?:是 C#三元运算符

viewModel.Numeric = numericBox.Value == null ? null : (double?)(numericBox.Value);

相当于

if (numericBox.Value == null) 
{
  viewModel.Numeric = null;
}
else 
{
  viewModel.Numeric = (double?)(numericBox.Value);
}