WPF：渲染时绑定和实际值之间的差异

我正在从事一个相当大的项目，这就是为什么我不能真正粘贴工作代码的原因，但也许你可以从阅读症状中给我一个提示，说明什么是错误的。否则，我必须看看如何在一个较小的项目中重新创建问题，并将其粘贴到这里

我有一个自定义控件，它继承自

TreeView

，我们称之为

MyTreeView

。此控件正在使用它自己的容器，我们将其称为

mytreevieItem

s

整件事都经过了设计和调整，看起来像一个家谱或组织结构图（水平而不是垂直，父母在上面，孩子在下面）。连接线在

MyTreeView

的

OnRender

过程中绘制

Protected Overrides Sub OnRender(drawingContext As DrawingContext)
    Dim bounds As ItemBounds = Nothing

    If (Me.ConnectorPen IsNot Nothing) Then
        Me.GetItemBounds(Me, bounds)
        Me.DrawConnections(Me.ConnectorPen, drawingContext, bounds)
    End If

    MyBase.OnRender(drawingContext)
End Sub

ConnectorPen

是一个类型为

Pen

的依赖属性，

ItemBounds

是一个小的层次化辅助类，包含所有

mytreeItem

内容的边界矩形

GetItemBounds

收集每个

MyTreeViewItem

内容的边界矩形

Private Sub GetItemBounds(parent As ItemsControl, ByRef bounds As ItemBounds)
    Dim tvi As MyTreeViewItem
    Dim topLeft As Point
    Dim bottomRight As Point
    Dim current As ItemBounds = Nothing

    For Each item As Object In parent.Items
        tvi = TryCast(parent.ItemContainerGenerator.ContainerFromItem(item), MyTreeViewItem)

        If (tvi IsNot Nothing) Then
            topLeft = tvi.Content.TranslatePoint(New Point(0, 0), Me)
            bottomRight = tvi.Content.TranslatePoint(New Point(tvi.Content.ActualWidth, tvi.Content.ActualHeight), Me)

            If (bounds Is Nothing) Then
                bounds = New ItemBounds
                bounds.Bounds = New Rect(topLeft, bottomRight)
                current = bounds
            Else
                current = New ItemBounds
                current.Bounds = New Rect(topLeft, bottomRight)
                bounds.Children.Add(current)
            End If
        End If

        Me.GetItemBounds(tvi, current)
    Next item
End Sub

<Style TargetType="{x:Type local:MyTreeViewItem}" BasedOn="{StaticResource {x:Type TreeViewItem}}">
    <Setter Property="ItemsPanel">
        <Setter.Value>
            <ItemsPanelTemplate>
                <StackPanel Orientation="Horizontal"
                            HorizontalAlignment="Center"
                            IsItemsHost="True"
                            Margin="0,20,0,0" />
            </ItemsPanelTemplate>
        </Setter.Value>
    </Setter>
    ...
</Style>

tvi.Content

是保存当前项目内容的

ContentPresenter

DrawConnections

根据收集的项目边界绘制连接线：

Private Sub DrawConnections(p As Pen, drawingContext As DrawingContext, bounds As ItemBounds)
    Dim minChildTop As Double
    Dim middle As Double

    If (bounds Is Nothing) OrElse (bounds.Children Is Nothing) OrElse (bounds.Children.Count = 0) Then
        Exit Sub
    End If

    If (bounds.Children.Count > 1) Then
        minChildTop = bounds.Children.Min(Of Double)(Function(x As ItemBounds) x.Bounds.Top)
        middle = bounds.Bounds.Bottom + ((minChildTop - bounds.Bounds.Bottom) / 2)

        drawingContext.DrawLine(p, bounds.Bounds.BottomCenter,
                                   New Point(bounds.Bounds.BottomCenter.X, middle))
        drawingContext.DrawLine(p, New Point(bounds.Children.First.Bounds.TopCenter.X, middle),
                                   New Point(bounds.Children.Last.Bounds.TopCenter.X, middle))
    End If

    For Each item As ItemBounds In bounds.Children
        If (bounds.Children.Count > 1) Then
            drawingContext.DrawLine(p, New Point(item.Bounds.TopCenter.X, middle),
                                       item.Bounds.TopCenter)
        Else
            drawingContext.DrawLine(p, bounds.Bounds.BottomCenter,
                                       item.Bounds.TopCenter)
        End If

        Me.DrawConnections(p, drawingContext, item)
    Next item
End Sub

BottomCenter

和

TopCenter

是

Rect

的扩展方法，用于确定将上边缘或下边缘切成两个相同长度的两半的

点

到目前为止一切正常。父项与其子项之间的空间由添加到
StackPanel
的固定边距创建，该边距用作默认样式
mytreeItem
中的
ItemsPanel

Private Sub GetItemBounds(parent As ItemsControl, ByRef bounds As ItemBounds)
    Dim tvi As MyTreeViewItem
    Dim topLeft As Point
    Dim bottomRight As Point
    Dim current As ItemBounds = Nothing

    For Each item As Object In parent.Items
        tvi = TryCast(parent.ItemContainerGenerator.ContainerFromItem(item), MyTreeViewItem)

        If (tvi IsNot Nothing) Then
            topLeft = tvi.Content.TranslatePoint(New Point(0, 0), Me)
            bottomRight = tvi.Content.TranslatePoint(New Point(tvi.Content.ActualWidth, tvi.Content.ActualHeight), Me)

            If (bounds Is Nothing) Then
                bounds = New ItemBounds
                bounds.Bounds = New Rect(topLeft, bottomRight)
                current = bounds
            Else
                current = New ItemBounds
                current.Bounds = New Rect(topLeft, bottomRight)
                bounds.Children.Add(current)
            End If
        End If

        Me.GetItemBounds(tvi, current)
    Next item
End Sub

<Style TargetType="{x:Type local:MyTreeViewItem}" BasedOn="{StaticResource {x:Type TreeViewItem}}">
    <Setter Property="ItemsPanel">
        <Setter.Value>
            <ItemsPanelTemplate>
                <StackPanel Orientation="Horizontal"
                            HorizontalAlignment="Center"
                            IsItemsHost="True"
                            Margin="0,20,0,0" />
            </ItemsPanelTemplate>
        </Setter.Value>
    </Setter>
    ...
</Style>

现在，子项使用
ItemSpacing
提供的空间（这样可以工作），但连接线的绘制失败。看起来所有
mytreevieItem
s内容的边界矩形的收集在应用此边界之前完成

我已经尝试过使用
itemspacking
依赖项属性的
AffectsRender
和
affectsrange
设置，但没有任何帮助

您能告诉我，为什么使用固定页边距，以及当页边距来自绑定时为什么不起作用吗？
能否显示
OnRender
？我已根据描述复制了您的代码，但问题不存在。请在描述中添加更多代码。