当使用 RequestNavigate（即以编程方式）在视图/视图模型之间导航时，会按预期调用相应视图模型上的 IConfirmNavigationRequest 方法。但是，如果您通过单击选项卡来切换 TabControl 区域中的视图，则它不会调用这些方法。
这是预期和接受的行为吗？我能否实现棱镜行为来完成这项工作？
任何建议将不胜感激。
更新
我决定根据 Viktor 的反馈更彻底地解释这个问题。如果用户在屏幕上有未保存的编辑，我想阻止导航。切换标签恕我直言只是另一种导航方式。我希望 Prism 实现是一致的：以编程方式或其他方式导航应该具有相同的行为。
如果我要创建一个带有按钮的 ItemsControl，当单击时使用 RequestNavigate 进行导航（以有效地切换选项卡）它会起作用，但这不是问题的重点。
【问题讨论】：
我想我明白你的意思，我理解你为什么希望它调用 RequestNavigate 方法。
要回答您的问题，是的，这是设计使然，在切换选项卡时不应调用 RequestNavigate。 但是，您可以修改此行为以做您想做的事情。棱镜是开源的。您应该有源代码，您可以将项目添加到您的项目中，并轻松地逐步完成以下代码：
TabControlRegionAdapter - 使区域适应选项卡控件
public class TabControlRegionAdapter : RegionAdapterBase<TabControl>
{
/// <summary>
/// <see cref="Style"/> to set to the created <see cref="TabItem"/>.
/// </summary>
public static readonly DependencyProperty ItemContainerStyleProperty =
DependencyProperty.RegisterAttached("ItemContainerStyle", typeof(Style), typeof(TabControlRegionAdapter), null);
/// <summary>
/// Initializes a new instance of the <see cref="TabControlRegionAdapter"/> class.
/// </summary>
/// <param name="regionBehaviorFactory">The factory used to create the region behaviors to attach to the created regions.</param>
public TabControlRegionAdapter(IRegionBehaviorFactory regionBehaviorFactory)
: base(regionBehaviorFactory)
{
}
/// <summary>
/// Gets the <see cref="ItemContainerStyleProperty"/> property value.
/// </summary>
/// <param name="target">Target object of the attached property.</param>
/// <returns>Value of the <see cref="ItemContainerStyleProperty"/> property.</returns>
public static Style GetItemContainerStyle(DependencyObject target)
{
if (target == null) throw new ArgumentNullException("target");
return (Style)target.GetValue(ItemContainerStyleProperty);
}
/// <summary>
/// Sets the <see cref="ItemContainerStyleProperty"/> property value.
/// </summary>
/// <param name="target">Target object of the attached property.</param>
/// <param name="value">Value to be set on the <see cref="ItemContainerStyleProperty"/> property.</param>
public static void SetItemContainerStyle(DependencyObject target, Style value)
{
if (target == null) throw new ArgumentNullException("target");
target.SetValue(ItemContainerStyleProperty, value);
}
/// <summary>
/// Adapts a <see cref="TabControl"/> to an <see cref="IRegion"/>.
/// </summary>
/// <param name="region">The new region being used.</param>
/// <param name="regionTarget">The object to adapt.</param>
protected override void Adapt(IRegion region, TabControl regionTarget)
{
if (regionTarget == null) throw new ArgumentNullException("regionTarget");
bool itemsSourceIsSet = regionTarget.ItemsSource != null;
if (itemsSourceIsSet)
{
throw new InvalidOperationException(Resources.ItemsControlHasItemsSourceException);
}
}
/// <summary>
/// Attach new behaviors.
/// </summary>
/// <param name="region">The region being used.</param>
/// <param name="regionTarget">The object to adapt.</param>
/// <remarks>
/// This class attaches the base behaviors and also keeps the <see cref="TabControl.SelectedItem"/>
/// and the <see cref="IRegion.ActiveViews"/> in sync.
/// </remarks>
protected override void AttachBehaviors(IRegion region, TabControl regionTarget)
{
if (region == null) throw new ArgumentNullException("region");
base.AttachBehaviors(region, regionTarget);
if (!region.Behaviors.ContainsKey(TabControlRegionSyncBehavior.BehaviorKey))
{
region.Behaviors.Add(TabControlRegionSyncBehavior.BehaviorKey, new TabControlRegionSyncBehavior { HostControl = regionTarget });
}
}
/// <summary>
/// Creates a new instance of <see cref="Region"/>.
/// </summary>
/// <returns>A new instance of <see cref="Region"/>.</returns>
protected override IRegion CreateRegion()
{
return new SingleActiveRegion();
}
}
还有，TabControlRegionSyncBehavior。 这是您可以调用 RequestNavigate。
public class TabControlRegionSyncBehavior : RegionBehavior, IHostAwareRegionBehavior
{
///<summary>
/// The behavior key for this region sync behavior.
///</summary>
public const string BehaviorKey = "TabControlRegionSyncBehavior";
private static readonly DependencyProperty IsGeneratedProperty =
DependencyProperty.RegisterAttached("IsGenerated", typeof(bool), typeof(TabControlRegionSyncBehavior), null);
private TabControl hostControl;
/// <summary>
/// Gets or sets the <see cref="DependencyObject"/> that the <see cref="IRegion"/> is attached to.
/// </summary>
/// <value>A <see cref="DependencyObject"/> that the <see cref="IRegion"/> is attached to.
/// This is usually a <see cref="FrameworkElement"/> that is part of the tree.</value>
public DependencyObject HostControl
{
get
{
return this.hostControl;
}
set
{
TabControl newValue = value as TabControl;
if (newValue == null)
{
throw new InvalidOperationException(Resources.HostControlMustBeATabControl);
}
if (IsAttached)
{
throw new InvalidOperationException(Resources.HostControlCannotBeSetAfterAttach);
}
this.hostControl = newValue;
}
}
/// <summary>
/// Override this method to perform the logic after the behavior has been attached.
/// </summary>
protected override void OnAttach()
{
if (this.hostControl == null)
{
throw new InvalidOperationException(Resources.HostControlCannotBeNull);
}
this.SynchronizeItems();
this.hostControl.SelectionChanged += this.OnSelectionChanged;
this.Region.ActiveViews.CollectionChanged += this.OnActiveViewsChanged;
this.Region.Views.CollectionChanged += this.OnViewsChanged;
}
/// <summary>
/// Gets the item contained in the <see cref="TabItem"/>.
/// </summary>
/// <param name="tabItem">The container item.</param>
/// <returns>The item contained in the <paramref name="tabItem"/> if it was generated automatically by the behavior; otherwise <paramref name="tabItem"/>.</returns>
protected virtual object GetContainedItem(TabItem tabItem)
{
if (tabItem == null) throw new ArgumentNullException("tabItem");
if ((bool)tabItem.GetValue(IsGeneratedProperty))
{
return tabItem.Content;
}
return tabItem;
}
/// <summary>
/// Override to change how TabItem's are prepared for items.
/// </summary>
/// <param name="item">The item to wrap in a TabItem</param>
/// <param name="parent">The parent <see cref="DependencyObject"/></param>
/// <returns>A tab item that wraps the supplied <paramref name="item"/></returns>
protected virtual TabItem PrepareContainerForItem(object item, DependencyObject parent)
{
TabItem container = item as TabItem;
if (container == null)
{
object dataContext = GetDataContext(item);
container = new TabItem();
container.Content = item;
container.Style = TabControlRegionAdapter.GetItemContainerStyle(parent);
container.DataContext = dataContext; // To run with SL 2
container.Header = dataContext; // To run with SL 3
container.SetValue(IsGeneratedProperty, true);
}
return container;
}
/// <summary>
/// Undoes the effects of the <see cref="PrepareContainerForItem"/> method.
/// </summary>
/// <param name="tabItem">The container element for the item.</param>
protected virtual void ClearContainerForItem(TabItem tabItem)
{
if (tabItem == null) throw new ArgumentNullException("tabItem");
if ((bool)tabItem.GetValue(IsGeneratedProperty))
{
tabItem.Content = null;
}
}
/// <summary>
/// Creates or identifies the element that is used to display the given item.
/// </summary>
/// <param name="item">The item to get the container for.</param>
/// <param name="itemCollection">The parent's <see cref="ItemCollection"/>.</param>
/// <returns>The element that is used to display the given item.</returns>
protected virtual TabItem GetContainerForItem(object item, ItemCollection itemCollection)
{
if (itemCollection == null) throw new ArgumentNullException("itemCollection");
TabItem container = item as TabItem;
if (container != null && ((bool)container.GetValue(IsGeneratedProperty)) == false)
{
return container;
}
foreach (TabItem tabItem in itemCollection)
{
if ((bool)tabItem.GetValue(IsGeneratedProperty))
{
if (tabItem.Content == item)
{
return tabItem;
}
}
}
return null;
}
/// <summary>
/// Return the appropriate data context. If the item is a FrameworkElement it cannot be a data context in Silverlight, so we use its data context.
/// Otherwise, we just us the item as the data context.
/// </summary>
private static object GetDataContext(object item)
{
FrameworkElement frameworkElement = item as FrameworkElement;
return frameworkElement == null ? item : frameworkElement.DataContext;
}
private void SynchronizeItems()
{
List<object> existingItems = new List<object>();
if (this.hostControl.Items.Count > 0)
{
// Control must be empty before "Binding" to a region
foreach (object childItem in this.hostControl.Items)
{
existingItems.Add(childItem);
}
}
foreach (object view in this.Region.Views)
{
TabItem tabItem = this.PrepareContainerForItem(view, this.hostControl);
this.hostControl.Items.Add(tabItem);
}
foreach (object existingItem in existingItems)
{
this.Region.Add(existingItem);
}
}
private void OnSelectionChanged(object sender, SelectionChangedEventArgs e)
{
// e.OriginalSource == null, that's why we use sender.
if (this.hostControl == sender)
{
foreach (TabItem tabItem in e.RemovedItems)
{
object item = this.GetContainedItem(tabItem);
// check if the view is in both Views and ActiveViews collections (there may be out of sync)
if (this.Region.Views.Contains(item) && this.Region.ActiveViews.Contains(item))
{
this.Region.Deactivate(item);
}
}
foreach (TabItem tabItem in e.AddedItems)
{
object item = this.GetContainedItem(tabItem);
if (!this.Region.ActiveViews.Contains(item))
{
this.Region.Activate(item);
}
}
}
}
private void OnActiveViewsChanged(object sender, NotifyCollectionChangedEventArgs e)
{
if (e.Action == NotifyCollectionChangedAction.Add)
{
this.hostControl.SelectedItem = this.GetContainerForItem(e.NewItems[0], this.hostControl.Items);
}
else if (e.Action == NotifyCollectionChangedAction.Remove
&& this.hostControl.SelectedItem != null
&& e.OldItems.Contains(this.GetContainedItem((TabItem)this.hostControl.SelectedItem)))
{
this.hostControl.SelectedItem = null;
}
}
private void OnViewsChanged(object sender, NotifyCollectionChangedEventArgs e)
{
if (e.Action == NotifyCollectionChangedAction.Add)
{
int startingIndex = e.NewStartingIndex;
foreach (object newItem in e.NewItems)
{
TabItem tabItem = this.PrepareContainerForItem(newItem, this.hostControl);
this.hostControl.Items.Insert(startingIndex, tabItem);
}
}
else if (e.Action == NotifyCollectionChangedAction.Remove)
{
foreach (object oldItem in e.OldItems)
{
TabItem tabItem = this.GetContainerForItem(oldItem, this.hostControl.Items);
this.hostControl.Items.Remove(tabItem);
this.ClearContainerForItem(tabItem);
}
}
}
}
当然，您必须弄清楚在哪里调用 RequestNavigate，这样您才能真正取消 TabSelectionChanging。不幸的是，WPF 中不存在此事件。我会求助于Josh Smith How to Prevent a TabItem from changing推荐的技巧
【讨论】：
我从您的问题中了解到，您希望切换选项卡调用 IConfirmNavigationRequest。当您从实现此接口的视图/viewModel 导航时，将调用此接口中的方法。
但是，您在 TabControl 中切换选项卡时遇到的不是导航请求。 TabControl 中的所有视图都已经处理了导航操作，并且所有视图都已经在 TabControl(Your Region) 中。那么当你切换标签时你会做什么呢？您只在您的区域内激活视图。以前活动的视图被停用。
我真的不知道你想完成什么。我无法想象我为什么要阻止某人切换标签。但是你可以通过使用 IActiveAware 接口来尝试。你可以从这个blog得到想法
编辑
实现 OnDeactivate 以询问用户是否要在停用视图之前保存更改
实现 OnActivate 以调用 RequestNavigate 到现有的视图。你可以阅读关于在 Prism 中导航到现有视图documentation。
禁用所有其他 tabItems 并在保存更改后再次启用它们（不好的方法）
我真的不是专家，但我认为你没有更多选择了
【讨论】：