跟踪属性更改中的更改

Question

我想将我的可观察视图模型对象集合过滤为更新的对象。我已经订阅了每个视图模型的属性更改事件。但我不确定如何跟踪对象，因此最终结果将只是在 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
            }
       }

Answer 1

我只是将它们存储在 HashSet 中。这样，您就不必担心跟踪集合中已有的内容：

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)
    {
        ...
    }
}