C# 跟踪更改的属性中的更改

我想将viewmodel对象的可观察集合过滤到更新的对象。我已为每个viewmodel订阅了属性更改事件。但我不确定如何跟踪对象，以便最终结果仅是UI中更新的对象

    ProgramViewModel Cur=new ProgramViewModel(prg);
                        Cur.PropertyChanged += new PropertyChangedEventHandler(Cur_PropertyChanged);
                        program.Add(Cur);
//here program is my observable collection of viewmodels

 void Cur_PropertyChanged(object sender, PropertyChangedEventArgs e)
        {  
          //What will be the code that will filter out only updated objects
            throw new NotImplementedException();
        }

//Now in my Save Event handler

private void Save_Click(object sender, RoutedEventArgs e)
        {
          foreach (ProgramViewModel model in program)
            {
                //I need only updated objects here to be added to database
            }
       }

---

我只想将它们存储在一个

散列集中。这样，您就不必担心跟踪哪些已在收藏中：

private readonly HashSet<ProgramViewModel> changedPrograms = new HashSet<ProgramViewModel>();

void Cur_PropertyChanged(object sender, PropertyChangedEventArgs e)
{  
    changedPrograms.Add((ProgramViewModel)sender);
}

private void Save_Click(object sender, RoutedEventArgs e)
{
    foreach (ProgramViewModel model in changedPrograms)
    {
        ...
    }
}

private readonly HashSet changedPrograms=new HashSet（）；
void Cur_PropertyChanged（对象发送方，propertychangedventargs e）
{  
更改程序。添加（（ProgramViewModel）发送方）；
}
私有无效保存\单击（对象发送者，路由目标）
{
foreach（changedPrograms中的ProgramViewModel模型）
{
...
}
}