如何让设为0像素的Grid子元素（Border）跟随列调整大小？

问题根源在于左侧面板折叠时，对应列宽被设为0 Pixel，此时GridSplitter无法对宽度为0的列进行调整。我们可以利用GridSplitter的DragStarted事件（拖动开始时触发），自动展开面板并恢复列宽，让拖动操作正常生效。

步骤1：修改XAML，添加GridSplitter的DragStarted事件 #

给GridSplitter绑定事件：

<GridSplitter Grid.Column="1" VerticalAlignment="Stretch" HorizontalAlignment="Stretch" 
              DragStarted="GridSplitter_DragStarted"/>

步骤2：后台添加事件处理逻辑 #

在Repro类中新增事件处理方法：

private void GridSplitter_DragStarted(object sender, DragStartedEventArgs e)
{
    // 若左侧面板处于折叠状态，自动触发展开逻辑
    if (PanelVisibility == Visibility.Collapsed)
    {
        PanelVisibility = Visibility.Visible;
        ContainerGrid.ColumnDefinitions[2].Width = _videoPanelWidth;
        ContainerGrid.ColumnDefinitions[0].Width = _propPanelWidth;
    }
}

补充说明 #

• 选择DragStarted的原因：它在拖动动作启动瞬间触发，能在用户开始调整前就恢复面板状态，保证拖动体验连贯。DragDelta会在拖动过程中才触发，存在延迟感；Mouse系列事件则需要额外处理更多状态判断，不如DragStarted直接高效。
• 原有手动折叠/展开逻辑无需改动，仅在拖动开始时自动触发展开，不影响按钮的手动控制功能。

修改后的完整代码 #

XAML部分

<UserControl x:Class="SublimeTriptych.control.Repro"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:SublimeTriptych.control"
             mc:Ignorable="d" 
             d:DesignHeight="450" d:DesignWidth="800">
    <Grid Name="ContainerGrid">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="160"/>
            <ColumnDefinition Width="4"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>

        <Border Grid.ColumnSpan="1" Background="Gold"
                Visibility="{Binding PanelVisibility, Mode=OneWay, RelativeSource={RelativeSource AncestorType=local:Repro}}"/>
        <GridSplitter Grid.Column="1" VerticalAlignment="Stretch" HorizontalAlignment="Stretch" 
                      DragStarted="GridSplitter_DragStarted"/>
        <Border Grid.Column="2" Background="Orange"/>

        <DockPanel Grid.ColumnSpan="3" Grid.Column="0" VerticalAlignment="Bottom">
            <Button HorizontalAlignment="Center" Command="{Binding SwitchVisibilityCommand, RelativeSource={RelativeSource AncestorType=local:Repro}}">👁</Button>
        </DockPanel>
    </Grid>
</UserControl>

后台代码部分

public partial class Repro : INotifyPropertyChanged
{
    private ICommand? _switchVisibilityCommand;
    private Visibility _panelVisibility = Visibility.Visible;
    private GridLength _videoPanelWidth;
    private GridLength _propPanelWidth;

    public Repro()
    {
        InitializeComponent();
    }

    public ICommand SwitchVisibilityCommand => _switchVisibilityCommand ?? (_switchVisibilityCommand =
        new DelegateCommandListen(
            s =>
            {
                PanelVisibility = PanelVisibility == Visibility.Visible ? Visibility.Collapsed : Visibility.Visible;
                if (PanelVisibility == Visibility.Collapsed)
                {
                    _propPanelWidth = ContainerGrid.ColumnDefinitions[0].Width;
                    _videoPanelWidth = ContainerGrid.ColumnDefinitions[2].Width;
                    ContainerGrid.ColumnDefinitions[0].Width = new GridLength(0, GridUnitType.Pixel);
                    ContainerGrid.ColumnDefinitions[2].Width = new GridLength(1, GridUnitType.Star);
                }
                else
                {
                    ContainerGrid.ColumnDefinitions[2].Width = _videoPanelWidth;
                    ContainerGrid.ColumnDefinitions[0].Width = _propPanelWidth;
                }
            },
            s => true));

    public Visibility PanelVisibility
    {
        get => _panelVisibility;
        set => SetField(ref _panelVisibility, value);
    }

    private void GridSplitter_DragStarted(object sender, DragStartedEventArgs e)
    {
        if (PanelVisibility == Visibility.Collapsed)
        {
            PanelVisibility = Visibility.Visible;
            ContainerGrid.ColumnDefinitions[2].Width = _videoPanelWidth;
            ContainerGrid.ColumnDefinitions[0].Width = _propPanelWidth;
        }
    }

    #region inpc

    public event PropertyChangedEventHandler? PropertyChanged;

    protected virtual void OnPropertyChanged([CallerMemberName] string? propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    protected bool SetField<T>(ref T field, T value, [CallerMemberName] string? propertyName = null)
    {
        if (EqualityComparer<T>.Default.Equals(field, value)) return false;
        field = value;
        OnPropertyChanged(propertyName);
        return true;
    }

    #endregion
}

内容的提问来源于stack exchange，提问作者Soleil