Question

下面的XAML代码工作正常，但我希望扩展器按钮位于列表框和网格之间。如果我设置ExpandDirection =“Left”，则按钮位于列表框和网格之间，但按钮上的方向指示器会让用户感到困惑 - 它在展开时指向右侧，在未展开时指向左侧。我希望方向指示器按照它在ExpandDirection =“Right”时的工作方式工作，但我想要ExpandDirection =“Left”的功能。

<DockPanel>
    <Expander ExpandDirection="Right">
        <ListBox>
            <ListBoxItem>Item One</ListBoxItem>
            <ListBoxItem>Item Two</ListBoxItem>
            <ListBoxItem>Item Three</ListBoxItem>
            <ListBoxItem>Item Four</ListBoxItem>
            <ListBoxItem>Item Five</ListBoxItem>
        </ListBox>
    </Expander>
        <Grid Background="AliceBlue">
          <TextBlock >
            Other Content
          </TextBlock>
        </Grid>
</DockPanel>

Answer 1

使用Expression Blend，编辑Expander当前模板的副本，转到XAML获取模板，将“ExpanderLeftHeaderStyle”重命名为“ExpanderRightHeaderStyle”，将“ExpanderRightHeaderStyle”重命名为“ExpanderLeftHeaderStyle”。

Answer 2

我更喜欢使用我后来写过的DockedExpander类（代码包含在下面）。该类自动设置它所停靠的DockPanel的任何一侧。

例如，在：

<DockPanel>
  <edf:DockedExpander DockPanel.Dock="Left">
    <ListBox ...
  </edf:DockedExpander>

  <Grid ...

</DockPanel>

扩展器将从左侧打开，按钮朝向正确的方向。但改为：

  <edf:DockedExpander DockPanel.Dock="Right">

会自动调整扩展器的其余部分以匹配。与“顶部”和“底部”对接相同。

我实现了DockedExpander，因为将数百行WPF的内部代码复制到我的项目中的想法对我来说是令人憎恶的。此外，我的DockedExpander控件自动适应新的主题样式，因为它读取WPF的内部样式。

以下是DockedExpander类的代码：

public class DockedExpander : Expander
{
  static DockedExpander()
  {
    _directions = new Dictionary<Dock, DirectionData>();
    _directions[Dock.Left]   = new DirectionData { Reverse = Dock.Right,  ExpandDirection = ExpandDirection.Right };
    _directions[Dock.Right]  = new DirectionData { Reverse = Dock.Left,   ExpandDirection = ExpandDirection.Left  };
    _directions[Dock.Top]    = new DirectionData { Reverse = Dock.Bottom, ExpandDirection = ExpandDirection.Down  };
    _directions[Dock.Bottom] = new DirectionData { Reverse = Dock.Top,    ExpandDirection = ExpandDirection.Up    };

    DockPanel.DockProperty.OverrideMetadata(typeof(DockedExpander), new FrameworkPropertyMetadata
    {
      PropertyChangedCallback = (obj, e) => ((DockedExpander)obj).UpdateExpandDirection()
    });

    ExpandDirectionProperty.OverrideMetadata(typeof(DockedExpander), new FrameworkPropertyMetadata
    {
      PropertyChangedCallback = (obj, e) => { throw new ArgumentException("Cannot set ExpandDirection because DockedExpander always computes its ExpandDirection from the DockPanel.Dock property"); }
    });
  }

  public override void OnApplyTemplate()
  {
    base.OnApplyTemplate();
    UpdateExpandDirection();
  }

  private void UpdateExpandDirection()
  {
    // Can't use GetTemplateChild because non-PART_ names are not guaranteed to stay the same
    var dockPanel = FindTwoElementDockPanelUnder(this);
    var headerSite = dockPanel.Children[0];
    var expandSite = dockPanel.Children[1];

    // Compute the docking
    Dock myDock = DockPanel.GetDock(this);
    DirectionData myDockData = _directions[myDock];

    DockPanel.SetDock(headerSite, myDockData.Reverse);
    DockPanel.SetDock(expandSite, myDock);
    headerSite.SetValue(FrameworkElement.StyleProperty, myDockData.HeaderSiteStyle);
  }

  private static Dictionary<Dock, DirectionData> _directions;
  private class DirectionData
  {
    public Dock Reverse;
    public ExpandDirection ExpandDirection;
    public Style HeaderSiteStyle
    {
      get
      {
        if(_headerSiteStyle==null)
        {
          var expander = new Expander { ExpandDirection = this.ExpandDirection };
          expander.BeginInit();
          expander.EndInit();
          expander.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
          var headerSite = FindTwoElementDockPanelUnder(expander).Children[0];
          _headerSiteStyle = ((FrameworkElement)headerSite).Style;
        }
        return _headerSiteStyle;
      }
    }
    private Style _headerSiteStyle;
  }

  private static DockPanel FindTwoElementDockPanelUnder(DependencyObject visual)
  {
    while(true)
      switch(VisualTreeHelper.GetChildrenCount(visual))
      {
        case 1: visual = VisualTreeHelper.GetChild(visual, 0); continue;
        case 2: return visual as DockPanel;
        default: return null;
      }
  }
}

像往常一样，您需要在XAML中使用命名空间声明（xmlns）才能使用自定义控件。

如何将扩展器锚定到ListBox的右侧？

2 个答案: