使用INotifyPropertyChanged有什么问题？

Question

我正在关注有关WPF和数据绑定的PluralSight教程。我的代码在尝试实现INotifyPropertyChanged时出错。

public class Employee : INotifyPropertyChanged 
{
    public string Name { get; set; }
    public string Title { get; set; }

    public static Employee getEmployee()
    {
        var emp = new Employee() { Name = "Tom", Title = "Developer" };
        return emp;
    }

    public event PropertyChangedEventHandler PropertyChanged;
    private void OnPropertyChanged( [CallerMemberName] string caller = "")
    {
        if ( PropertyChanged != null)
        {

            PropertyChanged (this, 
                 new PropertyChangingEventArgs (caller));

        }
    }
}

错误发生在最后一条语句上（在if语句的末尾），说：

  

＆＃34;无法从System.ComponentModel.PropertyChangingEventArgs转换   到System.ComponentModel.PropertyChangedEventArgs＆＃34;

Answer 1

错误并没有真正说明，它说它无法从PropertyChan ging EventArgs转换为PropertyChan ged EventArgs。所以使用正确的参数类名：

public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged([CallerMemberName] string caller = "")
{
    if (PropertyChanged != null)
     {
        PropertyChanged(this,
                 new PropertyChangedEventArgs(caller));

    }
}

Answer 2

您使用的是错误的事件arg。当您应该使用PropertyChangingEventArgs

时PropertyChangedEventArgs

private void OnPropertyChanged( [CallerMemberName] string caller = "")    
{
    if ( PropertyChanged != null)
    {    
        PropertyChanged (this, new PropertyChangedEventArgs (caller));    
    }    
}