PropertyChanged ObservableCollection中ViewModel的事件

Question

我有一个可观察的viewmodel对象集合。如何在创建集合时为我的集合中的每个视图模型订阅Property Changed事件，并跟踪哪些已更改，以便我可以将它们更新到我的数据库。

Answer 1

我相信下面的代码可以作为如何解决您的问题的一个例子。在这个例子中，MyCollection是一个属性ViewModel对象。 ViewModel实现INotifyPropertyChanged接口。

private void AddCollectionListener() 
    { 
     if (MyCollection != null) 
     { 
      MyCollection.CollectionChanged += 
       new System.Collections.Specialized.NotifyCollectionChangedEventHandler(MyCollection_CollectionChanged); 
     } 
    } 

    void MyCollection_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e) 
    { 
     // Remove Listeners to each item that has been removed 
     foreach (object oldItem in e.OldItems) 
     { 
      ViewModel viewModel = oldItem as ViewModel; 

      if (viewModel != null) 
      { 
       viewModel.PropertyChanged -= viewModel_PropertyChanged; 
      } 
     } 

     // Add Listeners to each item that has been added 
     foreach (object newItem in e.NewItems) 
     { 
      ViewModel viewModel = newItem as ViewModel; 

      if (viewModel != null) 
      { 
       viewModel.PropertyChanged += new PropertyChangedEventHandler(viewModel_PropertyChanged); 
      } 
     } 
    } 

    void viewModel_PropertyChanged(object sender, PropertyChangedEventArgs e) 
    { 
     // TODO: Property Changed Logic 

     switch (e.PropertyName) 
     { 
      case "MyPropertyName": 
       // TODO: Perform logic necessary when MyPropertyName changes 
       break; 
      default: 
       // TODO: Perform logic for all other property changes. 
       break; 
     } 
    }