ObservableCollection 中 ViewModel 的 PropertyChanged 事件

Question

我有一个可观察的视图模型对象集合。如何在创建集合中的每个视图模型时订阅它们的 Property Changed 事件并跟踪哪些视图模型已更改，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示例。在此示例中，MyCollection 是 ViewModel 对象的属性。 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;
        }
    }