Why property changed value is null after changing the property value?

Can anyone tell me why PropertyChanged value comes null in INotifyPropertyChanged. I have a property and I change its value, but when it enters in NotifyPropertyChanged method the value of PropertyChanged is null. Following is my code :

  public class WorkOrder : INotifyPropertyChanged
  {

   public string _orderDays="0 Days";

    public string OrderDays 
    { 
        get { return _orderDays; }
        set
        {
            if (_orderDays == value)
                return;
            _orderDays = value;

            NotifyPropertyChanged("OrderDays");
        }  
    }

    public event PropertyChangedEventHandler PropertyChanged;

    // This method is called by the Set accessor of each property.
    // The CallerMemberName attribute that is applied to the optional propertyName
    // parameter causes the property name of the caller to be substituted as an argument.
    public void NotifyPropertyChanged([CallerMemberName]String propertyName =null )
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

this is the xaml where I bind the value

<Label x:Name="lblTicketDate" Text="{Binding OrderDays}" 
    Grid.Row="1" HorizontalOptions="CenterAndExpand"
    VerticalOptions="EndAndExpand"  />
Jon Skeet
people
quotationmark

but when it enters in NotifyPropertyChangd method the value of PropertyChanged is null

That just means that nothing has subscribed to the event yet. Beyond events, a delegate instances refers to one or more actions to execute when the delegate is invoked - a null reference is used to represent "0 actions".

If you use:

var order = new WorkOrder();
// Or whatever's useful instead of Console.WriteLine
order.PropertyChanged += (sender, args) => Console.WriteLine(e.PropertyName);
order.OrderDays = "Different";

then you'll see the event being raised.

people

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