[Silverlight入门系列]使用MVVM模式(2)：集合Model /ObservableCollection/ICollectionView

INotifyCollectionChanged在上一篇讲了《[Silverlight入门系列]使用MVVM模式(1)：MVVM核心概念 》，今天讲一下集合Model。所谓集合Model就是给ItemsControl，如DataGrid，Combobox等绑定的集合数据模型。另外，通过定制ItemsControl的数据模板（DataTemplate），还可以控制集合对象中每一项的显示。实现很简单，但数据源集合对象必须继承IEnumerable接口，为了让目标属性与数据源集合的更新（不但包括元素的修改，还包括元素的增加和删除）保持同步，数据源集合还必须实现INotifyPropertyChanged接口和INotifyCollectionChanged接口。

ObservableCollection

在Silverlight中创建数据源集合可以使用内建的ObservableCollection类，因为ObservableCollection类既实现了INotifyPropertyChanged接口，又实现了INotifyCollectionChanged接口。使用ObservableCollection类不但可以实现Add、Remove、Clear和Insert操作，还可以触发PropertyChanged事件。

    using System.Collections.ObjectModel;
 2     using System.Collections;
 3 
 4     public class MyModelCollection : ObservableCollection<MyModel>
 5     {
 6         public MyModelCollection()
 7         {
 8         }
 9 
10         public MyModelCollection(IEnumerable MyModels)
11         {
12             foreach (MyModel h in MyModels)
13                 this.Add(h);
14         }
15 
16         public void AddRange(IEnumerable MyModels)
17         {
18             foreach (MyModel h in MyModels)
19                 this.Add(h);
20         }
21     }
22 
23     public class MyModel
24     {
25         public int ModelID { get; set; }
26         public string ModelName { get; set; }
27     }
28 
29     public class MyViewModel
30     {
31         public MyModelCollection MyModelDataCollection { get; set; }
32         public MyViewModel(MyModelCollection modelCollection)
33         {
34             MyModelDataCollection = modelCollection;
35         }
36     }

集合Model绑定到ItemControl也很简单：

        private MyViewModel viewModel;
 2 
 3         public MainPage()
 4         {
 5             InitializeComponent();
 6 
 7             MyModel m1 = new MyModel() { ModelID = 1, ModelName = "abc" };
 8             MyModel m2 = new MyModel() { ModelID = 2, ModelName = "def" };
 9 
10             viewModel = new MyViewModel(new MyModelCollection(new List<MyModel>() { m1, m2 }));
11 
12             this.DataContext = viewModel;
13 
14             this.dataGrid1.ItemsSource = viewModel.MyModelDataCollection;
15             this.dataGrid1.AutoGenerateColumns = true;
16 
17             this.comboBox1.ItemsSource = viewModel.MyModelDataCollection;
18             this.comboBox1.DisplayMemberPath = "ModelName";
19             this.comboBox1.SelectedValuePath = "ModelID";
20 
21             this.comboBox1.SelectionChanged += new SelectionChangedEventHandler(comboBox1_SelectionChanged);
22         }
23 
24         void comboBox1_SelectionChanged(object sender, SelectionChangedEventArgs e)
25         {
26             this.textBlock1.Text = "Selected value: " + this.comboBox1.SelectedValue;
27         }

ICollectionView / PagedCollectionView

虽然上述的ObservableCollection很好用而且继承了INotifyPropertyChanged接口，有些时候我们需要对集合进行排序、过滤、分页等操作，这个时候就需要用ICollectionView接口，同样继承了

INotifyCollectionChanged接口。ICollectionView接口在Silverlight下有个子类：PagedCollectionView，在WPF下有个子类：ListCollectionView.

PagedCollectionView例子:

C#:

public class MyViewModel : INotifyPropertyChanged
 2 {
 3     public ICollectionView Customers { get; private set; }
 4 
 5     public MyViewModel( ObservableCollection<Customer> customers )
 6     {
 7         // Initialize the CollectionView for the underlying model
 8         // and track the current selection.
 9          Customers = new PagedCollectionView( customers );
10         Customers.CurrentChanged +=
11                            new EventHandler( SelectedItemChanged );
12     }
13 
14     private void SelectedItemChanged( object sender, EventArgs e )
15     {
16         Customer current = Customers.CurrentItem as Customer;
17         ...
18     }
19 }

XAML:

<ListBox ItemsSource="{Binding Path=Customers}">
2     <ListBox.ItemTemplate>
3         <DataTemplate>
4             <StackPanel>
5                 <TextBlock Text="{Binding Path=Name}"/>
6             </StackPanel>
7         </DataTemplate>
8     </ListBox.ItemTemplate>
9  </ListBox>