写在前面：在（一）中，介绍了TreeView控件MVVM模式下数据绑定的方法。在这篇文章中，将总结给节点添加事件的方法，这样说有些不对，总之实现的效果就是点击某个节点，将出现对应于该节点的页面或者数据。（我这里用的方法肯定不是最好的，但是是我能想到的最佳方法了，WPF初学者，希望大家多多指教。）
Example#1: 实现下图功能，点击左侧treeview姓名节点，在右侧会出现响应的detailed information. 可以将ID的textbox中的text属性绑定到treeview中SelectedItem
先构造两个类，一个是User，一个是TreeNode。User是TreeNode的一个属性。
public class User
{
public string Key { get; set; }
public string Name { get; set; }
public int? Age { get; set; }
public User()
{
Key = null;
Name = null;
Age = null;
}
}User
public class TreeNode
{
public int NodeID { get; set; }
public int ParentID { get; set; }
public string NodeName { get; set; }
public List<TreeNode> ChildNodes { get; set; }
public User user { get; set; }
public TreeNode()
{
ChildNodes = new List<TreeNode>();
user = new User();
}
}TreeNode
绑定：
<TreeView Grid.Column="0" FontSize="15" ItemsSource="{Binding Path=Nodes}" x:Name="treeview">
<TreeView.ItemTemplate>
<HierarchicalDataTemplate DataType="{x:Type local:TreeNode}" ItemsSource="{Binding Path=ChildNodes}">
<Label Content="{Binding Path=NodeName}"/>
</HierarchicalDataTemplate>
</TreeView.ItemTemplate>
</TreeView>
<TextBox Text="{Binding ElementName=treeview, Path=SelectedItem.user.Key}" Canvas.Left="70" Width="200" Canvas.Top="8"
FontSize="15"/>
<TextBox Text="{Binding ElementName=treeview, Path=SelectedItem.user.Age}" Canvas.Left="70" Width="200" Canvas.Top="8"
FontSize="15"/>上面两句TextBox控件，就是将项目中名为“treeview"的控件的SelectedItem.user.Key和SeletedItem.user.Age的值绑定到Text属性中。这样点”Lily"节点，右侧就会出现相应的信息。
Example#2:
上面的例子比较简单，第二个例子将button控件作为treeviewitem，并给button控件绑定一个Command。
场景描述：左侧是treeview，其中每个treeviewitem的元素都是button控件，点击每个节点，中间的listview中会出现符合条件的学生的姓名，比如，是Grade1的学生有Lucy, Tom和Lily三人。是Grade2Class1的学生有Sam和Jack两人。点击listview中的学生姓名，右侧会显示学生的ID和Age信息。
TreeView部分的XAML代码：
<TreeView Grid.Column="0" FontSize="15" ItemsSource="{Binding Path=Nodes}">
<TreeView.ItemTemplate>
<HierarchicalDataTemplate DataType="{x:Type local:TreeNode}" ItemsSource="{Binding Path=ChildNodes}">
<Button Content="{Binding NodeName}" Command="{Binding DataContext.TreeViewCommand,
RelativeSource={RelativeSource AncestorType=local:MainWindow}}" CommandParameter="{Binding Path=NodeID}"
Background="White" BorderThickness="0"/>
</HierarchicalDataTemplate>
</TreeView.ItemTemplate>
</TreeView>可以看见，TreeViewItem元素从Label变成了Button。其中Button控件绑定了一个TreeViewCommand。这里需要指明绑定的是DataContext下的TreeViewCommand，否则默认的是TreeNode类型中的TreeViewCommand属性。因此下面这句是非常关键的。
Command="{Binding DataContext.TreeViewCommand,
RelativeSource={RelativeSource AncestorType=local:MainWindow}}" CommandParameter="{Binding Path=NodeID}"ListView部分的XAML代码：
<ListView Name="listview" Grid.Column="1" ItemsSource="{Binding Users}" IsSynchronizedWithCurrentItem="True"
BorderBrush="DarkGray" BorderThickness="5">
<ListView.View>
<GridView>
<GridViewColumn Header="Name" DisplayMemberBinding="{Binding Path=Name}" Width="auto"/>
</GridView>
</ListView.View>
</ListView>ViewModel代码：
public class ViewModel :INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private List<User> userlist = new List<User>();
private List<TreeNode> nodes;
public List<TreeNode> Nodes
{
get { return nodes; }
set { nodes = value;
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs("Nodes"));
}
}
private List<User> users = new List<User>();
public List<User> Users
{
get { return users; }
set { users = value;
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs("Users"));
}
}
public DelegateCommand TreeViewCommand { get; }
public ViewModel()
{
// 初始化Nodes和Users，一般Users是要访问数据库得到的，这里进行了简化。
InitiateNodes();
InitiateUsers();
TreeViewCommand = new DelegateCommand(TreeViewCommandHandler);
}
private void TreeViewCommandHandler(object sender, DelegateCommandEventArgs e)
{
int id = Convert.ToInt32(e.Parameter);
switch (id)
{
case 1:
Users = userlist.Where(x => x.GradeNum == 1).ToList();
break;
case 2:
Users = userlist.Where(x => x.GradeNum == 2).ToList();
break;
case 3:
Users = userlist.Where(x => x.GradeNum == 3).ToList();
break;
case 4:
Users = userlist.Where(x => x.GradeNum == 1 && x.ClassNum == 1).ToList();
break;
case 5:
Users = userlist.Where(x => x.GradeNum == 1 && x.ClassNum == 2).ToList();
break;
case 6:
Users = userlist.Where(x => x.GradeNum == 2 && x.ClassNum == 1).ToList();
break;
case 7:
Users = userlist.Where(x => x.GradeNum == 2 && x.ClassNum == 2).ToList();
break;
case 8:
Users = userlist.Where(x => x.GradeNum == 3 && x.ClassNum == 1).ToList();
break;
case 9:
Users = userlist.Where(x => x.GradeNum == 3 && x.ClassNum == 2).ToList();
break;
}
}
#region Initial methods
private void InitiateNodes()
{
List<TreeNode> _nodes = new List<TreeNode>()
{
new TreeNode()
{
ParentID=0,NodeID=1,NodeName="Grade1"
},
new TreeNode()
{
ParentID=0,NodeID=2,NodeName="Grade2"
},
new TreeNode()
{
ParentID=0, NodeID=3, NodeName="Grade3"
},
new TreeNode(){ParentID=1,NodeID=4,NodeName="Class1"},
new TreeNode(){ParentID=1,NodeID=5,NodeName="Class2"},
new TreeNode(){ParentID=2,NodeID=6,NodeName="Class1"},
new TreeNode(){ParentID=2, NodeID=7, NodeName="Class2"},
new TreeNode(){ParentID=3, NodeID=8, NodeName="Class1"},
new TreeNode(){ParentID=3, NodeID=9, NodeName="Class2"}
};
Nodes = getChildNodes(0, _nodes);
}
private List<TreeNode> getChildNodes(int parentID, List<TreeNode> nodes)
{
List<TreeNode> mainNodes = nodes.Where(x => x.ParentID == parentID).ToList();
List<TreeNode> otherNodes = nodes.Where(x => x.ParentID != parentID).ToList();
foreach (TreeNode node in mainNodes)
node.ChildNodes = getChildNodes(node.NodeID, otherNodes);
return mainNodes;
}
private void InitiateUsers()
{
User Lily = new User()
{
Name = "Lily",
Age = 12,
GradeNum = 1,
ClassNum = 1
};
User Tom = new User()
{
Name = "Tom",
Age = 11,
GradeNum = 1,
ClassNum = 1
};
User Lucy = new User()
{
Name = "Lucy",
Age = 12,
GradeNum = 1,
ClassNum = 2
};
User Sam = new User()
{
Name = "Sam",
Age = 13,
GradeNum = 2,
ClassNum = 1
};
User Jack = new User() { Name = "Jack", Age = 13, GradeNum = 2, ClassNum = 1 };
User Ray = new User() { Name = "Ray", Age = 13, GradeNum = 2, ClassNum = 2 };
User Lisa = new User() { Name = "Lisa", Age = 14, GradeNum = 3, ClassNum = 1 };
User Liz = new User() { Name = "Liz", Age = 14, GradeNum = 3, ClassNum = 2 };
userlist.Add(Liz);
userlist.Add(Lisa);
userlist.Add(Sam);
userlist.Add(Lucy);
userlist.Add(Tom);
userlist.Add(Lily);
userlist.Add(Jack);
userlist.Add(Ray);
}
#endregion
}ViewModel
其中有两个类，DelegateCommand和DelegateCommandEventArgs，是继承自ICommand，然后委托方法的。
public class DelegateCommand : ICommand
{
// 定义一个名为SimpleEventHandler的委托，两个参数，一个object类，一个是自定义的DelegateCommandEventArgs类
public delegate void SimpleEventHandler(object sender, DelegateCommandEventArgs e);
// handler是方法，别忘了，委托是用于定义方法的类
private SimpleEventHandler handler;
private bool isEnabled = true;
public DelegateCommand(SimpleEventHandler handler)
{
this.handler = handler;
}
public void Execute(object parameter)
{
this.handler(this, new DelegateCommandEventArgs(parameter));
}
public bool CanExecute(object parameter)
{
return this.isEnabled;
}
public event EventHandler CanExecuteChanged;
public bool IsEnabled
{
get { return this.isEnabled; }
set
{
this.isEnabled = value;
this.OnCanExecuteChanged();
}
}
private void OnCanExecuteChanged()
{
if (this.CanExecuteChanged != null)
this.CanExecuteChanged(this, EventArgs.Empty);
}
}DelegateCommand
public class DelegateCommandEventArgs : EventArgs
{
private object parameter;
public DelegateCommandEventArgs(object parameter)
{
this.parameter = parameter;
}
public object Parameter
{
get { return this.parameter; }
}
}DelegateCommandEventArgs
2020.06.25更新内容
之前使用Button控件作为TreeViewItem，然后为Button的Command属性绑定事件。更新为直接将事件绑定为TreeView的SelectedItemChanged属性，同样可以实现一样的效果。详情可见：
2021.12.14 关于TreeView控件的demo：
WPF中常用控件（TreeView, ComboBox, DataGrid, ListView)使用MVVM模式绑定的demo - 南风小斯
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