您也许可以使用我昨天在Prism 论坛上CommandParameterBehavior
发布的内容。它添加了丢失的行为,其中更改了要重新查询的原因。CommandParameter
Command
PropertyDescriptor.AddValueChanged
这里有一些复杂性,因为我试图避免如果您在没有稍后调用的情况下调用而导致的内存泄漏PropertyDescriptor.RemoveValueChanged
。我尝试通过在卸载 ekement 时取消注册处理程序来解决此问题。
IDelegateCommand
除非您使用 Prism(并且想要对 Prism 库进行与我相同的更改),否则您可能需要删除这些东西。另请注意,我们通常不在RoutedCommand
这里使用 s (我们使用 Prism 的几乎所有东西)所以如果我的调用引发某种破坏已知宇宙或任何东西的量子波函数崩溃级联,DelegateCommand<T>
请不要让我负责。CommandManager.InvalidateRequerySuggested
using System;
using System.ComponentModel;
using System.Windows;
using System.Windows.Input;
namespace Microsoft.Practices.Composite.Wpf.Commands
{
/// <summary>
/// This class provides an attached property that, when set to true, will cause changes to the element's CommandParameter to
/// trigger the CanExecute handler to be called on the Command.
/// </summary>
public static class CommandParameterBehavior
{
/// <summary>
/// Identifies the IsCommandRequeriedOnChange attached property
/// </summary>
/// <remarks>
/// When a control has the <see cref="IsCommandRequeriedOnChangeProperty" />
/// attached property set to true, then any change to it's
/// <see cref="System.Windows.Controls.Primitives.ButtonBase.CommandParameter" /> property will cause the state of
/// the command attached to it's <see cref="System.Windows.Controls.Primitives.ButtonBase.Command" /> property to
/// be reevaluated.
/// </remarks>
public static readonly DependencyProperty IsCommandRequeriedOnChangeProperty =
DependencyProperty.RegisterAttached("IsCommandRequeriedOnChange",
typeof(bool),
typeof(CommandParameterBehavior),
new UIPropertyMetadata(false, new PropertyChangedCallback(OnIsCommandRequeriedOnChangeChanged)));
/// <summary>
/// Gets the value for the <see cref="IsCommandRequeriedOnChangeProperty"/> attached property.
/// </summary>
/// <param name="target">The object to adapt.</param>
/// <returns>Whether the update on change behavior is enabled.</returns>
public static bool GetIsCommandRequeriedOnChange(DependencyObject target)
{
return (bool)target.GetValue(IsCommandRequeriedOnChangeProperty);
}
/// <summary>
/// Sets the <see cref="IsCommandRequeriedOnChangeProperty"/> attached property.
/// </summary>
/// <param name="target">The object to adapt. This is typically a <see cref="System.Windows.Controls.Primitives.ButtonBase" />,
/// <see cref="System.Windows.Controls.MenuItem" /> or <see cref="System.Windows.Documents.Hyperlink" /></param>
/// <param name="value">Whether the update behaviour should be enabled.</param>
public static void SetIsCommandRequeriedOnChange(DependencyObject target, bool value)
{
target.SetValue(IsCommandRequeriedOnChangeProperty, value);
}
private static void OnIsCommandRequeriedOnChangeChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
if (!(d is ICommandSource))
return;
if (!(d is FrameworkElement || d is FrameworkContentElement))
return;
if ((bool)e.NewValue)
{
HookCommandParameterChanged(d);
}
else
{
UnhookCommandParameterChanged(d);
}
UpdateCommandState(d);
}
private static PropertyDescriptor GetCommandParameterPropertyDescriptor(object source)
{
return TypeDescriptor.GetProperties(source.GetType())["CommandParameter"];
}
private static void HookCommandParameterChanged(object source)
{
var propertyDescriptor = GetCommandParameterPropertyDescriptor(source);
propertyDescriptor.AddValueChanged(source, OnCommandParameterChanged);
// N.B. Using PropertyDescriptor.AddValueChanged will cause "source" to never be garbage collected,
// so we need to hook the Unloaded event and call RemoveValueChanged there.
HookUnloaded(source);
}
private static void UnhookCommandParameterChanged(object source)
{
var propertyDescriptor = GetCommandParameterPropertyDescriptor(source);
propertyDescriptor.RemoveValueChanged(source, OnCommandParameterChanged);
UnhookUnloaded(source);
}
private static void HookUnloaded(object source)
{
var fe = source as FrameworkElement;
if (fe != null)
{
fe.Unloaded += OnUnloaded;
}
var fce = source as FrameworkContentElement;
if (fce != null)
{
fce.Unloaded += OnUnloaded;
}
}
private static void UnhookUnloaded(object source)
{
var fe = source as FrameworkElement;
if (fe != null)
{
fe.Unloaded -= OnUnloaded;
}
var fce = source as FrameworkContentElement;
if (fce != null)
{
fce.Unloaded -= OnUnloaded;
}
}
static void OnUnloaded(object sender, RoutedEventArgs e)
{
UnhookCommandParameterChanged(sender);
}
static void OnCommandParameterChanged(object sender, EventArgs ea)
{
UpdateCommandState(sender);
}
private static void UpdateCommandState(object target)
{
var commandSource = target as ICommandSource;
if (commandSource == null)
return;
var rc = commandSource.Command as RoutedCommand;
if (rc != null)
{
CommandManager.InvalidateRequerySuggested();
}
var dc = commandSource.Command as IDelegateCommand;
if (dc != null)
{
dc.RaiseCanExecuteChanged();
}
}
}
}