选定的TreeViewItem为null [英] Selected TreeViewItem is null
问题描述
我想为TreeView创建一个ContextMenu。 TreeView XAML：
I wanted to create a ContextMenu for my TreeView. TreeView XAML:
<helper:ExtendedTreeView Grid.Row="5" ItemsSource="{Binding OCFrage, Mode=TwoWay}" SelectedItem_="{Binding SelectedItem, Mode=TwoWay}" SelectedItemChanged="treeView1_SelectedItemChanged" x:Name="treeView1" Height="205" Width="215">
<helper:ExtendedTreeView.Resources>
<HierarchicalDataTemplate DataType="{x:Type model:T_Frage}" ItemsSource="{Binding Wertung, Mode=TwoWay}">
<TextBlock Text="{Binding Text}"/>
</HierarchicalDataTemplate>
</helper:ExtendedTreeView.Resources>
</helper:ExtendedTreeView>
而helper：ExtendedTreeView是此类：
while helper:ExtendedTreeView is this class:
public class ExtendedTreeView : TreeView
{
public ExtendedTreeView()
: base()
{
this.SelectedItemChanged += new RoutedPropertyChangedEventHandler<object>(self);
}
void self(object sender, RoutedPropertyChangedEventArgs<object> e)
{
if (SelectedItem != null)
{
SetValue(SelectedItem_Property, SelectedItem);
}
}
public object SelectedItem_
{
get { return (object)GetValue(SelectedItem_Property); }
set { SetValue(SelectedItem_Property, value); }
}
public static readonly DependencyProperty SelectedItem_Property = DependencyProperty.Register("SelectedItem_", typeof(object), typeof(ExtendedTreeView), new UIPropertyMetadata(null));
}
我正在使用它来绑定SelectedItem，并在ViewModel中使用它。
I'm using this for binding the SelectedItem and use it in my ViewModel.
我的TreeView具有标头，其类型为T_Frage，其节点的类型为T_Wertung，所以应该是
My TreeView has "Headers" which are of type T_Frage and their nodes are of type T_Wertung, so it would be
- T_Frage
- T_Wertung
- T_Wertung
- T_Wertung
...
我想为Headers创建一个ContextMenu。因此，如果用户单击类型为T_Frage的TreeViewItem，则应弹出ContextMenu。我已按照本指南 http：//canhandre.wordpress进行操作。 com / 2012/01/14 / wpf-treeview-with-contextmenu / ，而我目前正在CodeBehind中进行测试。问题是执行此代码时：
TreeViewItem selectedItem = treeView1.SelectedItem as TreeViewItem;treeView1.SelectedItem类型为T_Frage并具有它的值，但是当我分配给selectedItem，selectedItem仍然为null ...为什么？I wanted to create a ContextMenu for the Headers. So if the user clicks on the TreeViewItem of type T_Frage, a ContextMenu should popup. I've followed this guide http://canhandre.wordpress.com/2012/01/14/wpf-treeview-with-contextmenu/ and I'm doing it currently in the CodeBehind just to test it. The problem is that when this code is being executed:
TreeViewItem selectedItem = treeView1.SelectedItem as TreeViewItem;treeView1.SelectedItem is of type T_Frage and has it's values, but when I assign to selectedItem, selectedItem is still null... Why?编辑：在XAML中删除ItemsSource并创建普通的TreeViewItems
Removing the ItemsSource and creating normal TreeViewItems in XAML
<TreeViewItem Header="Edit" Name="Edit"> <TreeViewItem Header="Text"/> <TreeViewItem Header="Image"/> <TreeViewItem Header="Table"/> </TreeViewItem>将在此处分配值
TreeViewItem selectedItem = treeView1.SelectedItem作为TreeViewItem;。这意味着我无法在TreeView中将T_Frage类型的项目分配给TreeViewItem类型的变量。我应该如何为TreeView中非TreeViewItem类型的项目创建ContextMenu？就像您在上面看到的那样，将T_Frage的类型分配给TreeViewItem的结果将为null。will assign the value here
TreeViewItem selectedItem = treeView1.SelectedItem as TreeViewItem;. This means I can't assign a Item in my TreeView, which is of type T_Frage, to a variable of type TreeViewItem. How am I supposed to create a ContextMenu for a Item in my TreeView which is not of type TreeViewItem? Like you can see above, assigning the type of T_Frage to TreeViewItem will result as null.推荐答案
我知道现在是MVVM，不是CodeBehind，而是我想先在CodeBehind中对其进行测试，然后再在MVVM中进行所有操作，因为我认为立即在MVVM中进行操作会更困难...无论如何，这就是我想要的：
I know that it's MVVM now and not CodeBehind, but I just wanted to test it in CodeBehind first and then do it all in MVVM, because I thought doing it right away in MVVM would be harder... Anyway, this is what I wanted:
<helper:ExtendedTreeView Grid.Row="5" ItemsSource="{Binding OCFrage, Mode=TwoWay}" SelectedItem_="{Binding SelectedItem, Mode=TwoWay}" SelectedItemChanged="treeView1_SelectedItemChanged" x:Name="treeView1" Height="205" Width="215"> <TreeView.ContextMenu> <ContextMenu ItemsSource="{Binding OCContext}"/> </TreeView.ContextMenu) <helper:ExtendedTreeView.Resources> <HierarchicalDataTemplate DataType="{x:Type model:T_Frage}" ItemsSource="{Binding Wertung, Mode=TwoWay}"> <TextBlock Text="{Binding Text}"/> </HierarchicalDataTemplate> </helper:ExtendedTreeView.Resources> </helper:ExtendedTreeView>ViewModel：
ViewModel:
private object _selecteditem; public object SelectedItem { get { return _selecteditem; } set { OCContext = new ObservableCollection<T_Wertung>(); if (value is T_Frage) { T_Frage selected = (T_Frage)value; //do something with selected OCContext.Add(new T_Wertung(1,"Test",100)); } } RaisePropertyChanged(() => SelectedItem); } } private ObservableCollection<T_Wertung> _occontext; public ObservableCollection<T_Wertung> OCContext { get { if (_occontext == null) _occontext = new ObservableCollection<T_Wertung>(); return _occontext; } set { _occontext = value; RaisePropertyChanged(() => OCContext); } }因为我绑定到TreeView的SelectedItem ，请问SelectedItem是否为T_Frage类型。如果是真的，我将创建一个T_Frage类型的新变量，并将其上下文设置为SelectedItem的值。现在，我可以对此项目进行处理，然后将一个项目添加到名为
OCContext的ContextMenu列表中。当我右键单击该项目时，将弹出ContextMenu，它显示OCContext的项目。Since I'm binding to the SelectedItem of the TreeView, I can ask if the SelectedItem is of type T_Frage. If it's true, I'll create a new variable of type T_Frage and set it's context to the value of the SelectedItem. Now I can do something with this item and then add an item to the List of the ContextMenu named
OCContext. When I right click the item, the ContextMenu is being popped up and it shows the items ofOCContext.这篇关于选定的TreeViewItem为null的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
