[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。

1 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：

1 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#:

1 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:

1 < 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 >