延迟加载TreeViewItem自定义加载方法取决于它们的嵌套类型

Question

我正在使用自定义对象TreeView。

目标：在TreeViewItem.Expanded事件我想打电话给A.或B.LoadChilds()取决于嵌套式的实现延迟加载。

型号：

public class A 
{ 
    public A() 
    { 
     Childs = new ObservableCollection<B>(); 
    } 
    public string Name {get; set; } 
    public ObservableCollection<B> Childs { get; set; } 
    public void LoadChilds(DBConnection connection) //Type is unimportant 
    { 
     // adding childs 
    } 
} 

public class B 
{ 
    public B() 
    { 
     Childs = new ObservableCollection<B>(); //Yes, rekursiv 
    } 
    public string Name {get; set; } 
    public ObservableCollection<B> Childs { get; set; } 
    public void LoadChilds(DBConnection connection) 
    { 
     // adding childs 
    } 
} 

MainWindow.xaml

<TreeView x:Name="Tree"> 
    <TreeView.Resources> 
     <HierarchicalDataTemplate DataType="{x:Type model:A}" ItemsSource="{Binding Childs}"> 
      <StackPanel Orientation="Horizontal" > 
       <TextBlock Text="{Binding Name}" /> 
      </StackPanel> 
     </HierarchicalDataTemplate> 
     <HierarchicalDataTemplate DataType="{x:Type model:B}" ItemsSource="{Binding Childs}"> 
      <StackPanel Orientation="Horizontal" > 
       <TextBlock Text="{Binding Name}" /> 
      </StackPanel> 
     </HierarchicalDataTemplate> 
    </TreeView.Resources> 
</TreeView> 

代码隐藏

//Init 
List<A> ListOfAs = getAs(dbConnection); 
Tree.ItemsSource = ListOfAs; 

问题：达成目标的最佳方式是什么？

Answer 1

肯定是有“漂亮”的方式 - 无在代码隐藏的事件处理程序中编写业务逻辑。

介绍的图模型类布尔IsExpanded，结合TreeViewItem.IsExpanded到该属性，并触发在设定器LoadChilds方法：

<TreeView x:Name="Tree"> 
    <TreeView.ItemContainerStyle> 
     <Style TargetType="TreeViewItem"> 
      <Setter Property="IsExpanded" Value="{Binding Path=IsExpanded, Mode=TwoWay}"/> 
     </Style> 
    </TreeView.ItemContainerStyle> 
    <TreeView.Resources> 
     <HierarchicalDataTemplate DataType="{x:Type model:A}" ItemsSource="{Binding Childs}"> 
      <StackPanel Orientation="Horizontal" > 
       <TextBlock Text="{Binding Name}" /> 
      </StackPanel> 
     </HierarchicalDataTemplate> 
     <HierarchicalDataTemplate DataType="{x:Type model:B}" ItemsSource="{Binding Childs}"> 
      <StackPanel Orientation="Horizontal" > 
       <TextBlock Text="{Binding Name}" /> 
      </StackPanel> 
     </HierarchicalDataTemplate> 
    </TreeView.Resources> 
</TreeView> 

public class A 
{ 
    public A() 
    { 
     // null is a placeholder. 
     // without any items TreeViewItem will not even show expander 
     // (Expand event won't work either) 
     Childs = new ObservableCollection<B>() { null }; 
    } 

    public string Name { get; set; } 

    private bool _isExpanded; 
    public bool IsExpanded 
    { 
     get 
     { 
      return _isExpanded; 
     } 
     set 
     { 
      _isExpanded = value; 
      // when node is expanded, RELOAD! 
      if (_isExpanded) 
       LoadChilds(); 
     } 
    } 

    public ObservableCollection<B> Childs { get; set; } 

    public void LoadChilds() 
    { 
     Childs.Clear(); 
     Childs.Add(new B() { Name = Guid.NewGuid().ToString() }); 
    } 
} 

B是在本试验例中几乎相同，但我想LoadChilds逻辑将在不同的真实应用程序

public class B 
{ 
    public B() 
    { 
     Childs = new ObservableCollection<B>() { null }; 
    } 

    public string Name { get; set; } 

    private bool _isExpanded; 
    public bool IsExpanded 
    { 
     get 
     { 
      return _isExpanded; 
     } 
     set 
     { 
      _isExpanded = value; 
      if (_isExpanded) 
       LoadChilds(); 
     } 
    } 

    public ObservableCollection<B> Childs { get; set; } 

    public void LoadChilds() 
    { 
     Childs.Clear(); 
     Childs.Add(new B() { Name = Guid.NewGuid().ToString() }); 
    } 
} 

Answer 2

您可以定义两个A和B实现的接口和流延展开TreeViewItem的DataContext这种类型：

public interface ICommon 
{ 
    string Name { get; set; } 
    void LoadChilds(DBConnection connection); 
} 

public class A : ICommon 
{ 
    public class A() 
    { 
     Childs = new ObservableCollection<B>(); 
    } 
    public string Name { get; set; } 
    public ObservableCollection<B> Childs { get; set; } 
    public void LoadChilds(DBConnection connection) //Type is unimportant 
    { 
     // adding childs 
    } 
} 

public class B : ICommon 
{ 
    public class B() 
    { 
     Childs = new ObservableCollection<B>(); //Yes, rekursiv 
    } 
    public string Name { get; set; } 
    public ObservableCollection<B> Childs { get; set; } 
    public void LoadChilds(DBConnection connection) 
    { 
     // adding childs 
    } 
} 

---

private void TreeView_Expanded(object sender, RoutedEventArgs e) 
{ 
    TreeViewItem tvi = e.OriginalSource as TreeViewItem; 
    ICommon obj = tvi.DataContext as ICommon; 
    if (obj != null) 
     obj.LoadChilds(...); 

}