我有一个带有Treeview控件的WPF应用程序。
当用户单击树上的节点时，页面上的其他TextBox，ComboBox等控件将填充适当的值。
然后，用户可以更改这些值，并通过单击“保存”按钮保存其更改。
但是，如果用户选择了另一个Treeview节点而未保存其更改，我想显示警告并取消该选择的机会。
... XAML
<TreeView Name="TreeViewThings"
...
TreeViewItem.Unselected="TreeViewThings_Unselected"
TreeViewItem.Selected="TreeViewThings_Selected" >
Visual Basic ...
Sub TreeViewThings_Unselected(ByVal sender As System.Object, _
ByVal e As System.Windows.RoutedEventArgs)
Dim OldThing As Thing = DirectCast(e.OriginalSource.DataContext, Thing)
If CancelDueToUnsavedChanges(OldThing) Then
'put canceling code here
End If
End Sub
Sub TreeViewThings_Selected(ByVal sender As System.Object, _
ByVal e As System.Windows.RoutedEventArgs)
Dim NewThing As Thing = DirectCast(e.OriginalSource.DataContext, Thing)
PopulateControlsFromThing(NewThing)
End Sub
如何取消这些取消选择/选择事件？
更新：我问过一个后续问题......
How do I properly handle a PreviewMouseDown event with a MessageBox confirmation?
答案 0 :(得分：11)
<强>更新
已实现我可以将逻辑放在SelectedItemChanged中。一个小清洁解决方案。
Xaml
<TreeView Name="c_treeView"
SelectedItemChanged="c_treeView_SelectedItemChanged">
<TreeView.ItemContainerStyle>
<Style TargetType="{x:Type TreeViewItem}">
<Setter Property="IsSelected" Value="{Binding Path=IsSelected, Mode=TwoWay}" />
</Style>
</TreeView.ItemContainerStyle>
</TreeView>
代码背后。我有一些类是TreeView的ItemsSource，所以我创建了一个接口（MyInterface），为所有这些类公开了IsSelected属性。
private MyInterface m_selectedTreeViewItem = null;
private void c_treeView_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
{
if (m_selectedTreeViewItem != null)
{
if (e.NewValue == m_selectedTreeViewItem)
{
// Will only end up here when reversing item
// Without this line childs can't be selected
// twice if "No" was pressed in the question..
c_treeView.Focus();
}
else
{
if (MessageBox.Show("Change TreeViewItem?",
"Really change",
MessageBoxButton.YesNo,
MessageBoxImage.Question) != MessageBoxResult.Yes)
{
EventHandler eventHandler = null;
eventHandler = new EventHandler(delegate
{
c_treeView.LayoutUpdated -= eventHandler;
m_selectedTreeViewItem.IsSelected = true;
});
// Will be fired after SelectedItemChanged, to early to change back here
c_treeView.LayoutUpdated += eventHandler;
}
else
{
m_selectedTreeViewItem = e.NewValue as MyInterface;
}
}
}
else
{
m_selectedTreeViewItem = e.NewValue as MyInterface;
}
}
我没有发现在按“否”时没有恢复到上一个项目的任何情况。
答案 1 :(得分：3)
我必须解决同样的问题，但在我的应用程序中的多个树视图中。我派生了TreeView并添加了事件处理程序，部分使用了Meleak的解决方案，部分使用了此论坛的扩展方法：http://forums.silverlight.net/t/65277.aspx/1/10
我以为我会和你分享我的解决方案，所以这是我完整的可重复使用的TreeView来处理“取消节点更改”：
public class MyTreeView : TreeView
{
public static RoutedEvent PreviewSelectedItemChangedEvent;
public static RoutedEvent SelectionCancelledEvent;
static MyTreeView()
{
PreviewSelectedItemChangedEvent = EventManager.RegisterRoutedEvent("PreviewSelectedItemChanged", RoutingStrategy.Bubble,
typeof(RoutedPropertyChangedEventHandler<object>), typeof(MyTreeView));
SelectionCancelledEvent = EventManager.RegisterRoutedEvent("SelectionCancelled", RoutingStrategy.Bubble,
typeof(RoutedEventHandler), typeof(MyTreeView));
}
public event RoutedPropertyChangedEventHandler<object> PreviewSelectedItemChanged
{
add { AddHandler(PreviewSelectedItemChangedEvent, value); }
remove { RemoveHandler(PreviewSelectedItemChangedEvent, value); }
}
public event RoutedEventHandler SelectionCancelled
{
add { AddHandler(SelectionCancelledEvent, value); }
remove { RemoveHandler(SelectionCancelledEvent, value); }
}
private object selectedItem = null;
protected override void OnSelectedItemChanged(RoutedPropertyChangedEventArgs<object> e)
{
if (e.NewValue == selectedItem)
{
this.Focus();
var args = new RoutedEventArgs(SelectionCancelledEvent);
RaiseEvent(args);
}
else
{
var args = new RoutedPropertyChangedEventArgs<object>(e.OldValue, e.NewValue, PreviewSelectedItemChangedEvent);
RaiseEvent(args);
if (args.Handled)
{
EventHandler eventHandler = null;
eventHandler = delegate
{
this.LayoutUpdated -= eventHandler;
var treeViewItem = this.ContainerFromItem(selectedItem);
if (treeViewItem != null)
treeViewItem.IsSelected = true;
};
this.LayoutUpdated += eventHandler;
}
else
{
selectedItem = this.SelectedItem;
base.OnSelectedItemChanged(e);
}
}
}
}
public static class TreeViewExtensions
{
public static TreeViewItem ContainerFromItem(this TreeView treeView, object item)
{
if (item == null) return null;
var containerThatMightContainItem = (TreeViewItem)treeView.ItemContainerGenerator.ContainerFromItem(item);
return containerThatMightContainItem ?? ContainerFromItem(treeView.ItemContainerGenerator, treeView.Items, item);
}
private static TreeViewItem ContainerFromItem(ItemContainerGenerator parentItemContainerGenerator, ItemCollection itemCollection, object item)
{
foreach (var child in itemCollection)
{
var parentContainer = (TreeViewItem)parentItemContainerGenerator.ContainerFromItem(child);
var containerThatMightContainItem = (TreeViewItem)parentContainer.ItemContainerGenerator.ContainerFromItem(item);
if (containerThatMightContainItem != null)
return containerThatMightContainItem;
var recursionResult = ContainerFromItem(parentContainer.ItemContainerGenerator, parentContainer.Items, item);
if (recursionResult != null)
return recursionResult;
}
return null;
}
}
以下是一个使用示例（包含MyTreeView的窗口的代码隐藏）：
private void theTreeView_PreviewSelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
{
if (e.OldValue != null)
e.Handled = true;
}
private void theTreeView_SelectionCancelled(object sender, RoutedEventArgs e)
{
MessageBox.Show("Cancelled");
}
在树视图中选择第一个节点后，将取消所有其他节点更改并显示一个消息框。
答案 2 :(得分：2)
不是选择Selected / Unselected，而是更好的路线可以挂钩到PreviewMouseDown。处理Selected和Unselected事件的preblem是在收到通知时已经发生的事件。没有什么可以取消因为它已经发生了。
另一方面，预览事件可以取消。这不是您想要的确切事件，但它确实为您提供了防止用户选择其他节点的机会。
答案 3 :(得分：2)
您无法取消活动，例如Closing事件。但是，如果缓存最后选择的值，则可以撤消它。秘诀是您必须更改选择而不重新触发SelectionChanged事件。这是一个例子：
private object _LastSelection = null;
private void OnSelectionChanged(object sender, SelectionChangedEventArgs e)
{
if (IsUpdated)
{
MessageBoxResult result = MessageBox.Show("The current record has been modified. Are you sure you want to navigate away? Click Cancel to continue editing. If you click OK all changes will be lost.", "Warning", MessageBoxButton.OKCancel, MessageBoxImage.Hand);
switch (result)
{
case MessageBoxResult.Cancel:
e.Handled = true;
// disable event so this doesn't go into an infinite loop when the selection is changed to the cached value
PersonListView.SelectionChanged -= new SelectionChangedEventHandler(OnSelectionChanged);
PersonListView.SelectedItem = _LastSelection;
PersonListView.SelectionChanged += new SelectionChangedEventHandler(OnSelectionChanged);
return;
case MessageBoxResult.OK:
// revert the object to the original state
LocalDataContext.Persons.GetOriginalEntityState(_LastSelection).CopyTo(_LastSelection);
IsUpdated = false;
Refresh();
break;
default:
throw new ApplicationException("Invalid response.");
}
}
// cache the selected item for undo
_LastSelection = PersonListView.SelectedItem;
}
答案 4 :(得分：2)
CAMS_ARIES：
XAML：
代码：
private bool ManejarSeleccionNodoArbol(Object origen)
{
return true; // with true, the selected nodo don't change
return false // with false, the selected nodo change
}
private void Arbol_PreviewMouseDown(object sender, MouseButtonEventArgs e)
{
if (e.Source is TreeViewItem)
{
e.Handled = ManejarSeleccionNodoArbol(e.Source);
}
}
private void Arbol_PreviewKeyDown(object sender, KeyEventArgs e)
{
if (e.Source is TreeViewItem)
{
e.Handled=ManejarSeleccionNodoArbol(e.Source);
}
}
答案 5 :(得分：2)
你实际上不能将你的逻辑放入OnSelectedItemChanged方法中，如果逻辑存在，那么选择的项目实际上已经改变了。
正如另一张海报所暗示的那样，PreviewMouseDown处理程序是实现逻辑的更好的地方，但是，仍然需要完成大量的腿部工作。
以下是我的2美分：
首先是我实施的TreeView：
public class MyTreeView : TreeView
{
static MyTreeView( )
{
DefaultStyleKeyProperty.OverrideMetadata(
typeof(MyTreeView),
new FrameworkPropertyMetadata(typeof(TreeView)));
}
// Register a routed event, note this event uses RoutingStrategy.Tunnel. per msdn docs
// all "Preview" events should use tunneling.
// http://msdn.microsoft.com/en-us/library/system.windows.routedevent.routingstrategy.aspx
public static RoutedEvent PreviewSelectedItemChangedEvent = EventManager.RegisterRoutedEvent(
"PreviewSelectedItemChanged",
RoutingStrategy.Tunnel,
typeof(CancelEventHandler),
typeof(MyTreeView));
// give CLR access to routed event
public event CancelEventHandler PreviewSelectedItemChanged
{
add
{
AddHandler(PreviewSelectedItemChangedEvent, value);
}
remove
{
RemoveHandler(PreviewSelectedItemChangedEvent, value);
}
}
// override PreviewMouseDown
protected override void OnPreviewMouseDown(MouseButtonEventArgs e)
{
// determine which item is going to be selected based on the current mouse position
object itemToBeSelected = this.GetObjectAtPoint<TreeViewItem>(e.GetPosition(this));
// selection doesn't change if the target point is null (beyond the end of the list)
// or if the item to be selected is already selected.
if (itemToBeSelected != null && itemToBeSelected != SelectedItem)
{
bool shouldCancel;
// call our new event
OnPreviewSelectedItemChanged(out shouldCancel);
if (shouldCancel)
{
// if we are canceling the selection, mark this event has handled and don't
// propogate the event.
e.Handled = true;
return;
}
}
// otherwise we want to continue normally
base.OnPreviewMouseDown(e);
}
protected virtual void OnPreviewSelectedItemChanged(out bool shouldCancel)
{
CancelEventArgs e = new CancelEventArgs( );
if (PreviewSelectedItemChangedEvent != null)
{
// Raise our event with our custom CancelRoutedEventArgs
RaiseEvent(new CancelRoutedEventArgs(PreviewSelectedItemChangedEvent, e));
}
shouldCancel = e.Cancel;
}
}
一些扩展方法，支持TreeView在鼠标下找到对象。
public static class ItemContainerExtensions
{
// get the object that exists in the container at the specified point.
public static object GetObjectAtPoint<ItemContainer>(this ItemsControl control, Point p)
where ItemContainer : DependencyObject
{
// ItemContainer - can be ListViewItem, or TreeViewItem and so on(depends on control)
ItemContainer obj = GetContainerAtPoint<ItemContainer>(control, p);
if (obj == null)
return null;
// it is worth noting that the passed _control_ may not be the direct parent of the
// container that exists at this point. This can be the case in a TreeView, where the
// parent of a TreeViewItem may be either the TreeView or a intermediate TreeViewItem
ItemsControl parentGenerator = obj.GetParentItemsControl( );
// hopefully this isn't possible?
if (parentGenerator == null)
return null;
return parentGenerator.ItemContainerGenerator.ItemFromContainer(obj);
}
// use the VisualTreeHelper to find the container at the specified point.
public static ItemContainer GetContainerAtPoint<ItemContainer>(this ItemsControl control, Point p)
where ItemContainer : DependencyObject
{
HitTestResult result = VisualTreeHelper.HitTest(control, p);
DependencyObject obj = result.VisualHit;
while (VisualTreeHelper.GetParent(obj) != null && !(obj is ItemContainer))
{
obj = VisualTreeHelper.GetParent(obj);
}
// Will return null if not found
return obj as ItemContainer;
}
// walk up the visual tree looking for the nearest ItemsControl parent of the specified
// depObject, returns null if one isn't found.
public static ItemsControl GetParentItemsControl(this DependencyObject depObject)
{
DependencyObject obj = VisualTreeHelper.GetParent(depObject);
while (VisualTreeHelper.GetParent(obj) != null && !(obj is ItemsControl))
{
obj = VisualTreeHelper.GetParent(obj);
}
// will return null if not found
return obj as ItemsControl;
}
}
和最后，但并非最不重要的是利用RoutedEvent子系统的自定义EventArgs。
public class CancelRoutedEventArgs : RoutedEventArgs
{
private readonly CancelEventArgs _CancelArgs;
public CancelRoutedEventArgs(RoutedEvent @event, CancelEventArgs cancelArgs)
: base(@event)
{
_CancelArgs = cancelArgs;
}
// override the InvokeEventHandler because we are going to pass it CancelEventArgs
// not the normal RoutedEventArgs
protected override void InvokeEventHandler(Delegate genericHandler, object genericTarget)
{
CancelEventHandler handler = (CancelEventHandler)genericHandler;
handler(genericTarget, _CancelArgs);
}
// the result
public bool Cancel
{
get
{
return _CancelArgs.Cancel;
}
}
}
答案 6 :(得分：1)
由于在SelectedItemChanged已经更改后触发SelectedItem事件，此时您无法真正取消该事件。
您可以做的是听取鼠标点击并在SelectedItem更改之前取消它们。
答案 7 :(得分：1)
您可以创建从TreeView派生的自定义控件，然后覆盖OnSelectedItemChanged方法。
在调用base之前，您可以先使用CancelEventArgs参数触发自定义事件。如果parameter.Cancel变为true，则不要调用base，而是选择旧项（请注意再次调用OnSelectedItemChanged）。
不是最好的解决方案，但至少这会将逻辑保留在树控件内，并且选择更改事件不会发生超出需要的事件。此外，您无需关心用户是否单击树，使用键盘或以编程方式更改选择。
答案 8 :(得分：0)
我为1个树状视图解决了这个问题并且一次显示1个文档。此解决方案基于可附加到普通树视图的可附加行为：
<TreeView Grid.Column="0"
ItemsSource="{Binding TreeViewItems}"
behav:TreeViewSelectionChangedBehavior.ChangedCommand="{Binding SelectItemChangedCommand}"
>
<TreeView.ItemTemplate>
<HierarchicalDataTemplate ItemsSource="{Binding Children}">
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Name}"
ToolTipService.ShowOnDisabled="True"
VerticalAlignment="Center" Margin="3" />
</StackPanel>
</HierarchicalDataTemplate>
</TreeView.ItemTemplate>
<TreeView.ItemContainerStyle>
<Style TargetType="{x:Type TreeViewItem}">
<Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />
<Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
</Style>
</TreeView.ItemContainerStyle>
</TreeView>
并且行为的代码是：
/// <summary>
/// Source:
/// http://stackoverflow.com/questions/1034374/drag-and-drop-in-mvvm-with-scatterview
/// http://social.msdn.microsoft.com/Forums/de-DE/wpf/thread/21bed380-c485-44fb-8741-f9245524d0ae
///
/// Attached behaviour to implement the SelectionChanged command/event via delegate command binding or routed commands.
/// </summary>
public static class TreeViewSelectionChangedBehavior
{
#region fields
/// <summary>
/// Field of attached ICommand property
/// </summary>
private static readonly DependencyProperty ChangedCommandProperty = DependencyProperty.RegisterAttached(
"ChangedCommand",
typeof(ICommand),
typeof(TreeViewSelectionChangedBehavior),
new PropertyMetadata(null, OnSelectionChangedCommandChange));
/// <summary>
/// Implement backing store for UndoSelection dependency proeprty to indicate whether selection should be
/// cancelled via MessageBox query or not.
/// </summary>
public static readonly DependencyProperty UndoSelectionProperty =
DependencyProperty.RegisterAttached("UndoSelection",
typeof(bool),
typeof(TreeViewSelectionChangedBehavior),
new PropertyMetadata(false, OnUndoSelectionChanged));
#endregion fields
#region methods
#region ICommand changed methods
/// <summary>
/// Setter method of the attached ChangedCommand <seealso cref="ICommand"/> property
/// </summary>
/// <param name="source"></param>
/// <param name="value"></param>
public static void SetChangedCommand(DependencyObject source, ICommand value)
{
source.SetValue(ChangedCommandProperty, value);
}
/// <summary>
/// Getter method of the attached ChangedCommand <seealso cref="ICommand"/> property
/// </summary>
/// <param name="source"></param>
/// <returns></returns>
public static ICommand GetChangedCommand(DependencyObject source)
{
return (ICommand)source.GetValue(ChangedCommandProperty);
}
#endregion ICommand changed methods
#region UndoSelection methods
public static bool GetUndoSelection(DependencyObject obj)
{
return (bool)obj.GetValue(UndoSelectionProperty);
}
public static void SetUndoSelection(DependencyObject obj, bool value)
{
obj.SetValue(UndoSelectionProperty, value);
}
#endregion UndoSelection methods
/// <summary>
/// This method is hooked in the definition of the <seealso cref="ChangedCommandProperty"/>.
/// It is called whenever the attached property changes - in our case the event of binding
/// and unbinding the property to a sink is what we are looking for.
/// </summary>
/// <param name="d"></param>
/// <param name="e"></param>
private static void OnSelectionChangedCommandChange(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
TreeView uiElement = d as TreeView; // Remove the handler if it exist to avoid memory leaks
if (uiElement != null)
{
uiElement.SelectedItemChanged -= Selection_Changed;
var command = e.NewValue as ICommand;
if (command != null)
{
// the property is attached so we attach the Drop event handler
uiElement.SelectedItemChanged += Selection_Changed;
}
}
}
/// <summary>
/// This method is called when the selection changed event occurs. The sender should be the control
/// on which this behaviour is attached - so we convert the sender into a <seealso cref="UIElement"/>
/// and receive the Command through the <seealso cref="GetChangedCommand"/> getter listed above.
///
/// The <paramref name="e"/> parameter contains the standard EventArgs data,
/// which is unpacked and reales upon the bound command.
///
/// This implementation supports binding of delegate commands and routed commands.
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private static void Selection_Changed(object sender, RoutedPropertyChangedEventArgs<object> e)
{
var uiElement = sender as TreeView;
// Sanity check just in case this was somehow send by something else
if (uiElement == null)
return;
ICommand changedCommand = TreeViewSelectionChangedBehavior.GetChangedCommand(uiElement);
// There may not be a command bound to this after all
if (changedCommand == null)
return;
// Check whether this attached behaviour is bound to a RoutedCommand
if (changedCommand is RoutedCommand)
{
// Execute the routed command
(changedCommand as RoutedCommand).Execute(e.NewValue, uiElement);
}
else
{
// Execute the Command as bound delegate
changedCommand.Execute(e.NewValue);
}
}
/// <summary>
/// Executes when the bound boolean property indicates that a user should be asked
/// about changing a treeviewitem selection instead of just performing it.
/// </summary>
/// <param name="d"></param>
/// <param name="e"></param>
private static void OnUndoSelectionChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
TreeView uiElement = d as TreeView; // Remove the handler if it exist to avoid memory leaks
if (uiElement != null)
{
uiElement.PreviewMouseDown -= uiElement_PreviewMouseDown;
var command = (bool)e.NewValue;
if (command == true)
{
// the property is attached so we attach the Drop event handler
uiElement.PreviewMouseDown += uiElement_PreviewMouseDown;
}
}
}
/// <summary>
/// Based on the solution proposed here:
/// Source: http://stackoverflow.com/questions/20244916/wpf-treeview-selection-change
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private static void uiElement_PreviewMouseDown(object sender, MouseButtonEventArgs e)
{
// first did the user click on a tree node?
var source = e.OriginalSource as DependencyObject;
while (source != null && !(source is TreeViewItem))
source = VisualTreeHelper.GetParent(source);
var itemSource = source as TreeViewItem;
if (itemSource == null)
return;
var treeView = sender as TreeView;
if (treeView == null)
return;
bool undoSelection = TreeViewSelectionChangedBehavior.GetUndoSelection(treeView);
if (undoSelection == false)
return;
// Cancel the attempt to select an item.
var result = MessageBox.Show("The current document has unsaved data. Do you want to continue without saving data?", "Are you really sure?",
MessageBoxButton.YesNo, MessageBoxImage.Question, MessageBoxResult.No);
if (result == MessageBoxResult.No)
{
// Cancel the attempt to select a differnet item.
e.Handled = true;
}
else
{
// Lets disable this for a moment, otherwise, we'll get into an event "recursion"
treeView.PreviewMouseDown -= uiElement_PreviewMouseDown;
// Select the new item - make sure a SelectedItemChanged event is fired in any case
// Even if this means that we have to deselect/select the one and the same item
if (itemSource.IsSelected == true )
itemSource.IsSelected = false;
itemSource.IsSelected = true;
// Lets enable this to get back to business for next selection
treeView.PreviewMouseDown += uiElement_PreviewMouseDown;
}
}
#endregion methods
}
在此示例中，我显示了一个阻止消息框，以便在发生时阻止PreviewMouseDown事件。然后处理该事件以指示选择被取消或者不处理以使树视图本身通过选择即将被选择的项来处理事件。
如果用户决定继续执行，则行为会在viewmodel中调用绑定命令（PreviewMouseDown事件不会被附加行为处理，并且会调用绑定命令。
我想显示的消息框可以通过其他方式完成，但我认为它必须在发生时阻止事件，因为否则无法取消它（？）。所以，我能想到的唯一改进就是绑定一些字符串以使显示的消息可配置。
我写了一篇包含可下载样本的文章，因为这是一个难以解释的问题（人们必须对缺少的部分做出许多假设，并且可能并不总是被所有读者共享）
这是一篇包含我的结果的文章： http://www.codeproject.com/Articles/995629/Cancelable-TreeView-Navigation-for-Documents-in-WP
请评论此解决方案，如果您有改进的余地，请告诉我。