[Silverlight入门系列]使用MVVM模式(7)：ViewModel的INotifyPropertyChanged接口实现

本文说说ViewModel的这个INotifyPropertyChanged接口可以用来做啥？

 

举例1：我有个TabControl，里面放了很多View，每个由ViewModel控制，我想是想TabSelectionChanged就打开相应的ViewModel，怎么做？

解答：用ViewModel的INotifyPropertyChanged接口实现，因为TabItem作为一个选择器就有 IsSelected属性，把这个属性绑定到ViewModel的IsSelected字段，然后这个字段改变的时候用INotifyPropertyChanged接口实现通知即可。整个流程用MVVM实现非常整洁。

<TabControl ...>
2 <TabControl.ItemContainerStyle>
3 <Style TargetType="{x:Type TabItem}">
4 <Setter Property="IsSelected"
5                     Value="{Binding Path=IsSelected,Mode=TwoWay}"/>
6 </Style>
7 </TabControl.ItemContainerStyle>
8 </TabControl>

publicclass MyViewModel : INotifyPropertyChanged
 2 {
 3 privatebool _isLoaded;
 4 
 5 privatevoid Load()
 6     {
 7 // code
 8     }
 9 
10 privatebool _isSelected;
11 
12 publicbool IsSelected
13     {
14 get
15         {
16 returnthis._isSelected;
17         }
18 set
19         {
20 if (this._isSelected != value)
21             {
22 this._isSelected = value;
23 
24 if (this._isSelected &&!this._isLoaded)
25                 {
26 this.Load();
27 this._isLoaded =true;
28                 }
29 
30                 var propertyChanged =this.PropertyChanged;
31 if (propertyChanged !=null)
32                 {
33                     propertyChanged(this, new PropertyChangedEventArgs("IsSelected"));
34                 }
35             }
36         }
37     }
38 
39 publicevent PropertyChangedEventHandler PropertyChanged;
40 }

 

举例2：我有个TreeView，里面的项非常复杂，还需要惰性加载（点击了才取数据并展开），怎么用MVVM实现？彻底晕了

解答：还是用ViewModel的INotifyPropertyChanged接口实现，要使得你的视图没有代码，就要你不再把TreeView当成一个存储数据的地方，而是看做一个展现数据的地方，那么一切都将水到渠成。这就是ViewModel这个想法的由来。而用INotifyPropertyChanged接口可以神奇的实现它们之间的解耦。

<TreeView ItemsSource="{Binding FirstGeneration}">
 2 <TreeView.ItemContainerStyle>
 3 <!-- 
 4     This Style binds a TreeViewItem to a PersonViewModel. 
 5 -->
 6 <Style TargetType="{x:Type TreeViewItem}">
 7 <Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}"/>
 8 <Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay}"/>
 9 <Setter Property="FontWeight" Value="Normal"/>
10 <Style.Triggers>
11 <Trigger Property="IsSelected" Value="True">
12 <Setter Property="FontWeight" Value="Bold"/>
13 </Trigger>
14 </Style.Triggers>
15 </Style>
16 </TreeView.ItemContainerStyle>
17 
18 <TreeView.ItemTemplate>
19 <HierarchicalDataTemplate ItemsSource="{Binding Children}">
20 <TextBlock Text="{Binding Name}"/>
21 </HierarchicalDataTemplate>
22 </TreeView.ItemTemplate>
23 </TreeView>

 

publicclass PersonViewModel
 2 {
 3 public PersonViewModel(Person person)
 4     : this(person, null)
 5    {
 6    }
 7 
 8 private PersonViewModel(Person person, PersonViewModel parent)
 9   {
10     _person = person;
11     _parent = parent;
12 
13     _children =<span styl%