问题描述
我使用 TreeView 来显示对象层次结构，使用 Philipp Sumi's method 来组织使用转换器的异构数据。这有效。
但是，我现在想在 XAML 中添加 ContextMenus，这通常特定于用户单击的对象类型。由于使用 FolderItem 来表示多个类，因此多个对象类型可以共享相同的 <ContextMenu> 定义。
下面的示例显示了一个基本的 TreeView。猫和狗具有相同的 <ContextMenu> 定义。我能否更具体地定位 ContextMenu，以便仅在用户点击“Dogs”而不是“Cats”时显示“Walk all dogs”菜单？
我正在寻找类似于针对 Name 的 FolderItem 属性的内容（即逻辑为 [display context menu] if Name == "Dogs"。）
我当然可以使用带有右键单击事件的代码隐藏来实现此功能，并且到目前为止已经完成。只是以良好实践的名义尝试在 XAML 中做更多事情。
<Window x:Class="TestTreeView.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:TestTreeView"
mc:Ignorable="d"
Title="MainWindow" Height="450" Width="800">
<Window.Resources>
<local:SimpleFolderConverter x:Key="folderConverter" />
<HierarchicalDataTemplate DataType="{x:Type local:Pets}">
<HierarchicalDataTemplate.ItemsSource>
<MultiBinding Converter="{StaticResource folderConverter}"
ConverterParameter="Cats,Dogs">
<Binding Path="cats" />
<Binding Path="dogs" />
</MultiBinding>
</HierarchicalDataTemplate.ItemsSource>
<TextBlock Text="{Binding Path=description}" />
</HierarchicalDataTemplate>
<DataTemplate DataType="{x:Type local:Cat}">
<TextBlock Text="{Binding Path=Name}" />
</DataTemplate>
<DataTemplate DataType="{x:Type local:Dog}">
<TextBlock Text="{Binding Path=Name}" />
</DataTemplate>
<!-- data template for FolderItem instances -->
<HierarchicalDataTemplate DataType="{x:Type local:FolderItem}" ItemsSource="{Binding Path=Items}">
<StackPanel Orientation="Horizontal">
<StackPanel.ContextMenu>
<ContextMenu> <!-- This applies to more than one type of underlying object -->
<MenuItem Header="Walk all dogs"/>
</ContextMenu>
</StackPanel.ContextMenu>
<TextBlock Text="{Binding Path=Name}" />
</StackPanel>
</HierarchicalDataTemplate>
</Window.Resources>
<Grid>
<TreeView x:Name="treeView"/>
</Grid>
</Window>
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
Pets pets = new Pets();
pets.cats.Add(new Cat());
pets.dogs.Add(new Dog());
treeView.ItemsSource = new ObservableCollection<Pets>() { pets };
}
}
public class Pets {
public string description { get; set; } = "Pets";
public ObservableCollection<Cat> cats { get; set; } = new ObservableCollection<Cat>();
public ObservableCollection<Dog> dogs { get; set; } = new ObservableCollection<Dog>();
public IEnumerable<Pets> CollectionOfSelf
{
get { yield return this; }
}
}
public class Cat {
public string Name { get; set; } = "Socks";
}
public class Dog {
public string Name { get; set; } = "Fido";
}
public class FolderItem
{
#region Name
/// <summary>
/// The name that can be displayed or used as an ID to perform more complex styling.
/// </summary>
private string name;
/// <summary>
/// The name that can be displayed or used as an ID to perform more complex styling.
/// </summary>
public string Name
{
get { return name; }
set
{
//ignore if values are equal
if (value == name) return;
name = value;
OnPropertyChanged("Name");
}
}
private void OnPropertyChanged(string v)
{
//
}
#endregion
#region Items
/// <summary>
/// The child items of the folder.
/// </summary>
private IEnumerable items;
/// <summary>
/// The child items of the folder.
/// </summary>
public IEnumerable Items
{
get { return items; }
set
{
//ignore if values are equal
if (value == items) return;
items = value;
OnPropertyChanged("Items");
}
}
#endregion
public FolderItem()
{
}
/// <summary>
/// This method is invoked by WPF to render the object if
/// no data template is available.
/// </summary>
/// <returns>Returns the value of the <see cref="Name"/>
/// property.</returns>
public override string ToString()
{
return string.Format("{0}: {1}",GetType().Name,Name);
}
}
public class SimpleFolderConverter : IMultiValueConverter
{
/// <summary>
///
/// </summary>
/// <param name="values"></param>
/// <param name="targettype"></param>
/// <param name="parameter"></param>
/// <param name="culture"></param>
/// <returns></returns>
public object Convert(object[] values,Type targettype,object parameter,CultureInfo culture)
{
//get folder name listing...
string folder = parameter as string ?? "";
var folders = folder.Split(',').Select(f => f.Trim()).ToList();
//...and make sure there are no missing entries
while (values.Length > folders.Count) folders.Add(String.Empty);
//this is the collection that gets all top level items
List<object> items = new List<object>();
for (int i = 0; i < values.Length; i++)
{
//make sure were working with collections from here...
IEnumerable childs = values[i] as IEnumerable ?? new List<object> { values[i] };
string folderName = folders[i];
if (folderName != String.Empty)
{
//create folder item and assign children
FolderItem folderItem = new FolderItem { Name = folderName,Items = childs };
items.Add(folderItem);
}
else
{
//if no folder name was specified,move the item directly to the root item
foreach (var child in childs) { items.Add(child); }
}
}
return items;
}
public object[] ConvertBack(object value,Type[] targettypes,CultureInfo culture)
{
throw new NotSupportedException("Cannot perform reverse-conversion");
}
}
解决方法
我做过这样的事情。当用户选择一个项目时，我有一个名为 SelectedItem 的所选项目的属性。然后我可以使用基于 SelectedItem 属性的触发器来个性化 ContextMenu 的 MenuItems。特别是，我使用 SelectedItem 的属性来确定禁用哪个菜单项，但您也可以控制每个菜单项的可见性。
或者，虽然我还没有尝试过，但应该可以使用设置 ContextMenu 属性的触发器。
如果我正确理解了您的问题，您可以根据 ContextMenu 的 Name 使用带有 FolderItem 的 Style 应用不同的 DataTrigger：
<HierarchicalDataTemplate DataType="{x:Type local:FolderItem}" ItemsSource="{Binding Path=Items}">
<StackPanel Orientation="Horizontal">
<StackPanel.Style>
<Style TargetType="StackPanel">
<Style.Triggers>
<DataTrigger Binding="{Binding Name}" Value="Dogs">
<Setter Property="ContextMenu">
<Setter.Value>
<ContextMenu>
<MenuItem Header="Walk all dogs"/>
</ContextMenu>
</Setter.Value>
</Setter>
</DataTrigger>
<DataTrigger Binding="{Binding Name}" Value="Cats">
<Setter Property="ContextMenu">
<Setter.Value>
<ContextMenu>
<MenuItem Header="Walk all cats"/>
</ContextMenu>
</Setter.Value>
</Setter>
</DataTrigger>
</Style.Triggers>
</Style>
</StackPanel.Style>
<TextBlock Text="{Binding Path=Name}" />
</StackPanel>
</HierarchicalDataTemplate>