Question

我得到了客户报告的下面的堆栈跟踪。我不知道如何重现这个。我的WPF应用程序有相当数量的ComboBoxes;鉴于下面的堆栈跟踪，我不确定如何确定哪个ComboBox失败。有没有人见过这个？你能解释一下这个堆栈跟踪的内容吗？有什么想法吗？

System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Windows.Controls.ComboBox.CoerceIsSelectionBoxHighlighted(Object o, Object value)
   at System.Windows.DependencyObject.ProcessCoerceValue(DependencyProperty dp, PropertyMetadata metadata, EntryIndex& entryIndex, Int32& targetIndex, EffectiveValueEntry& newEntry, EffectiveValueEntry& oldEntry, Object& oldValue, Object baseValue, Object controlValue, CoerceValueCallback coerceValueCallback, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, Boolean skipBaseValueChecks)
   at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
   at System.Windows.DependencyObject.CoerceValue(DependencyProperty dp)
   at System.Windows.Controls.ComboBox.OnIsKeyboardFocusWithinChanged(DependencyPropertyChangedEventArgs e)
   at System.Windows.FocusWithinProperty.FireNotifications(UIElement uie, ContentElement ce, UIElement3D uie3D, Boolean oldValue)
   at System.Windows.ReverseInheritProperty.FirePropertyChangeInAncestry(DependencyObject element, Boolean oldValue, DeferredElementTreeState treeState, Action`2 originChangedAction)
   at System.Windows.ReverseInheritProperty.OnOriginValueChanged(DependencyObject oldOrigin, DependencyObject newOrigin, IList`1 otherOrigins, DeferredElementTreeState& oldTreeState, Action`2 originChangedAction)
   at System.Windows.Input.KeyboardDevice.ChangeFocus(DependencyObject focus, Int32 timestamp)
   at System.Windows.Input.KeyboardDevice.PostProcessInput(Object sender, ProcessInputEventArgs e)
   at System.Windows.Input.InputManager.RaiseProcessInputEventHandlers(ProcessInputEventHandler postProcessInput, ProcessInputEventArgs processInputEventArgs)
   at System.Windows.Input.InputManager.ProcessStagingArea()
   at System.Windows.Input.InputManager.ProcessInput(InputEventArgs input)
   at System.Windows.Input.InputProviderSite.ReportInput(InputReport inputReport)
   at System.Windows.Interop.HwndKeyboardInputProvider.ReportInput(IntPtr hwnd, InputMode mode, Int32 timestamp, RawKeyboardActions actions, Int32 scanCode, Boolean isExtendedKey, Boolean isSystemKey, Int32 virtualKey)
   at System.Windows.Interop.HwndKeyboardInputProvider.PossiblyDeactivate(IntPtr hwndFocus)
   at System.Windows.Interop.HwndKeyboardInputProvider.FilterMessage(IntPtr hwnd, WindowMessage message, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at System.Windows.Interop.HwndSource.InputFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)

Answer 1

这是代码（.NET 4.5.2）。 o不是ComboBox或HighlightedElement为空。

就个人而言，我的第一步是分发PDB，以便在堆栈跟踪中获取行号。

private static object CoerceIsSelectionBoxHighlighted(object o, object value)
{
    ComboBox comboBox = (ComboBox)o;
    return (!comboBox.IsDropDownOpen && comboBox.IsKeyboardFocusWithin) ||
           (comboBox.HighlightedInfo != null && comboBox.HighlightedElement.Content == comboBox._clonedElement);
}

private ComboBoxItem HighlightedElement
{
    get { return (_highlightedInfo == null) ? null : _highlightedInfo.Container as ComboBoxItem; }
}

Answer 2

我们有一个定制的过滤组合框，我们作为继承自组合框的用户控制而制作。在Windows 10计算机上，我们开始在数据网格行上的表单中过滤组合框中出现此错误。我们在DataGrid上的DataGrid.RowDetailsTemplate中有一个过滤的组合框。

为了让错误消失，我们在Filtered_Combobox类中覆盖了这个子。

Protected Overrides Sub OnIsKeyboardFocusWithinChanged(e As DependencyPropertyChangedEventArgs)
    Try


    Catch ex As Exception
    End Try
End Sub

注意：我们还没有在覆盖中放置任何代码，因为它似乎没有做任何事情（尽管崩溃了应用程序）。

Answer 3

我们在某些（没有时间到达精确范围）版本的运行时和窗口上遇到了类似的问题。

我们的一个组合框具有以下风格

<ComboBox.Style>
    <Style TargetType="{x:Type ComboBox}" BasedOn="{StaticResource {x:Type ComboBox}}">
        <Setter Property="IsDropDownOpen" Value="False"/>
            <Style.Triggers>
                <Trigger Property="IsKeyboardFocusWithin" Value="True">
                    <Setter Property="IsDropDownOpen" Value="True" />
                </Trigger>
            </Style.Triggers>
    </Style>

不知何故，有时会因选择突出显示而导致异常。也许这很有帮助。

Answer 4

最终为我们解决的问题是覆盖导致问题的事件：

Protected Overrides Sub OnIsKeyboardFocusWithinChanged(e As DependencyPropertyChangedEventArgs)
    Try
        'GW 2015-09-20 Added this override to prevent windows 10 crashes on comboboxes within forms within datagrids

    Catch ex As Exception
    End Try
End Sub

Answer 5

我和maiksaray分享的代码有类似的错误。对我来说，CoerceIsSelectionBoxHighlighted的NullReferenceException只发生在Windows 10上，而不是我的Windows 7开发机器上。它只发生在第一次单击组合框打开时。

就我而言，我在加载视图时以编程方式打开和关闭组合框：

public MyView()
{
    InitializeComponent();
    Loaded += OnLoaded;
}

private void comboBox1_DropDownOpened(object sender, EventArgs e)
{
    comboBox1.ItemsSource = MyClass.GetComboBoxList();
}

private void OnLoaded(object sender, RoutedEventArgs e)
{
   comboBox1.IsDropDownOpen = true;
   comboBox1.IsDropDownOpen = false;
}

我这样做是另一个问题的解决方法，如下所述： http://blog.elgaard.com/2009/09/03/wpf-making-combo-box-items-disabled-also-when-accessed-using-the-keyboard/

DevicesComboBox_DropDownOpened 完成后发生错误。但是，它只出现在 OnLoaded 代码中。如果我注释掉已加载+ = OnLoaded ，那么我没有收到错误。

我的解决方案是简单地避免以编程方式打开和关闭ComboBox。

ComboBox强制崩溃（不是我的代码）

5 个答案: