WPF DataGrid：滚动时减小列宽以适合其内容

Question

当我滚动垂直滚动条时，DataGrid 会在新可见行中的内容更大并超过之前的列宽时自动扩展列宽。没关系。

但是如果所有较大的行都被滚动并且新的可见行具有较小的内容宽度，DataGrid 不会减小列宽。有办法存档吗？

附加行为实现会很棒。

代码行为：

 public partial class MainWindow
    {
        public MainWindow()
        {
            InitializeComponent();
            var persons = new List<Person>();
            for (var i = 0; i < 20; i++)
                persons.Add(new Person() {Name = "Coooooooooooooool", Surname = "Super"});
            for (var i = 0; i < 20; i++)
                persons.Add(new Person() {Name = "Cool", Surname = "Suuuuuuuuuuuuuuper"});
            for (var i = 0; i < 20; i++)
                persons.Add(new Person() {Name = "Coooooooooooooool", Surname = "Super"});
            DG.ItemsSource = persons;
        }

        public class Person
        {
            public string Name { get; set; }
            public string Surname { get; set; }
        }
    }

XAML：

<Window
    x:Class="WpfApp4.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    Title="MainWindow"
    Width="400"
    Height="200"
    mc:Ignorable="d">
    <Grid>
        <DataGrid
            x:Name="DG"
            CanUserAddRows="False"
            CanUserDeleteRows="False"
            CanUserReorderColumns="False"
            CanUserResizeColumns="False"
            CanUserResizeRows="False"
            CanUserSortColumns="False" />
    </Grid>
</Window>

Answer 1

将LoadingRow 属性添加到您的Datagrid：

   <DataGrid x:Name="DG"
        CanUserAddRows="False"
        CanUserDeleteRows="False"
        CanUserReorderColumns="False"
        CanUserResizeColumns="False"
        CanUserResizeRows="False"
        CanUserSortColumns="False" LoadingRow="DG_LoadingRow">
    </DataGrid>

然后添加这段代码 在后面的代码中：

private void DG_LoadingRow(object sender, DataGridRowEventArgs e)
    {
        foreach (DataGridColumn c in DG.Columns)
            c.Width = 0;

        DG.UpdateLayout();

        foreach (DataGridColumn c in DG.Columns)
            c.Width = DataGridLength.Auto;
    }

这绝对不是最干净的解决方案，但它会在滚动时调整视图中的列的大小。

希望这会有所帮助。

---

你能把它包装成附加的行为吗？

1) 第一种选择是使用附加属性。

public class DataGridHelper : DependencyObject
{
    public static readonly DependencyProperty SyncedColumnWidthsProperty =
        DependencyProperty.RegisterAttached(
          "SyncedColumnWidths",
          typeof(Boolean),
          typeof(DataGridHelper),
          new FrameworkPropertyMetadata(false,
              FrameworkPropertyMetadataOptions.AffectsRender,
              new PropertyChangedCallback(OnSyncColumnsChanged)
          ));

    private static void OnSyncColumnsChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if (d is DataGrid dataGrid)
        {
            dataGrid.LoadingRow += SyncColumnWidths;
        }
    }

    private static void SyncColumnWidths(object sender, DataGridRowEventArgs e)
    {
        var dataGrid = (DataGrid)sender;

        foreach (DataGridColumn c in dataGrid.Columns)
            c.Width = 0;

        e.Row.UpdateLayout();

        foreach (DataGridColumn c in dataGrid.Columns)
            c.Width = DataGridLength.Auto;
    }

    public static void SetSyncedColumnWidths(UIElement element, Boolean value)
    {
        element.SetValue(SyncedColumnWidthsProperty, value);
    }
}

用法

<DataGrid
    ext:DataGridHelper.SyncedColumnWidths="True"
    ... />

2) 或者，行为提供了一种更加封装的方式来扩展功能（需要System.Windows.Interactivity）。

using System.Windows.Interactivity;

...

    public class SyncedColumnWidthsBehavior : Behavior<DataGrid>
    {
        protected override void OnAttached()
        {
            this.AssociatedObject.LoadingRow += this.SyncColumnWidths;
        }

        protected override void OnDetaching()
        {
            this.AssociatedObject.LoadingRow -= this.SyncColumnWidths;
        }

        private void SyncColumnWidths(object sender, DataGridRowEventArgs e)
        {
            var dataGrid = this.AssociatedObject;

            foreach (DataGridColumn c in dataGrid.Columns)
                c.Width = 0;

            e.Row.UpdateLayout();

            foreach (DataGridColumn c in dataGrid.Columns)
                c.Width = DataGridLength.Auto;
        }
    }

用法

xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"

...

    <DataGrid
        ... >
        <i:Interaction.Behaviors>
            <ext:SyncedColumnWidthsBehavior />
        </i:Interaction.Behaviors>
    </DataGrid>

行为提供了一种释放事件处理程序的简洁方式。虽然在这种情况下，即使我们不取消订阅附加属性，我们也不会造成内存泄漏（参考 Is it bad to not unregister event handlers?）。

Answer 2

对于延迟回答您的问题，我们深表歉意。

我这里的方法是捕获屏幕中的可见行并获取平均宽度并分配给列宽。

首先订阅了 ScrollViewer 的 ScrollChanged 事件。

       <DataGrid
        ScrollViewer.ScrollChanged="DG_ScrollChanged"
        x:Name="DG"
        CanUserAddRows="False"
        CanUserDeleteRows="False"
        CanUserReorderColumns="False"
        CanUserResizeColumns="False"
        CanUserResizeRows="False"
        CanUserSortColumns="False" />
</Grid>

通过使用ScrollChanged 和FindVisualChildren，我可以获得垂直偏移量。

我们可以从垂直偏移量获得行索引，最后一行的索引是使用 (int)scroll.VerticalOffset + (int)scroll.ViewportHeight - 1 计算的

     ScrollViewer scroll = null;
    private void DG_ScrollChanged(object sender, ScrollChangedEventArgs e)
    {
        // get the control once and then use its offset to get the row index
        if (scroll == null)
            scroll = MethodRepo.FindVisualChildren<ScrollViewer>((DependencyObject)sender).First(); 

        int firstRow = (int)scroll.VerticalOffset;
        int lastRow = (int)scroll.VerticalOffset + (int)scroll.ViewportHeight + 1;

        List<int> FirstColumnLength = new List<int>();
        List<int> SecondColumnLength = new List<int>();
        for (int i = firstRow; i < lastRow-1; i++)
        {
            FirstColumnLength.Add(Convert.ToString(persons[i].Name).Length);
            SecondColumnLength.Add(Convert.ToString(persons[i].Surname).Length);
        }

        DG.Columns[0].Width = FirstColumnLength.Max()*10;
        DG.Columns[1].Width = SecondColumnLength.Max() * 10;
    }

我还创建了一个静态类来获取 Visual 子级。

 public static class MethodRepo
{
    public static IEnumerable<T> FindVisualChildren<T>([NotNull] this DependencyObject parent) where T : DependencyObject
    {
        if (parent == null)
            throw new ArgumentNullException(nameof(parent));

        var queue = new Queue<DependencyObject>(new[] { parent });

        while (queue.Any())
        {
            var reference = queue.Dequeue();
            var count = VisualTreeHelper.GetChildrenCount(reference);

            for (var i = 0; i < count; i++)
            {
                var child = VisualTreeHelper.GetChild(reference, i);
                if (child is T children)
                    yield return children;

                queue.Enqueue(child);
            }
        }
    }
}