Question

我正在尝试创建虚拟统一网格，所以我从here中获取了一些代码，创建了一个可以设置列数的面板，并且它工作正常，它比标准统一网格快3-4倍（我在列表框的复杂项目模板上测试它有很多记录）。所以我想我将基本控件从Panel更改为VirtualizingStackPanel，但是一旦我这样做，就没有记录显示。任何想法为什么？这是我的工作代码：

更改以下内容以从VirtualizingPanel或VirtualizingStackPanel派生，它将不再起作用：（

public class MyUniformGrid : Panel // VirtualizingStackPanel
{
    public static readonly DependencyProperty ColumnsProperty = DependencyProperty.Register("Columns", typeof(int), typeof(MyUniformGrid), new FrameworkPropertyMetadata(1, FrameworkPropertyMetadataOptions.AffectsMeasure));

    public int Columns
    {
        set { SetValue(ColumnsProperty, value); }
        get { return (int)GetValue(ColumnsProperty); }
    }

    private int Rows => (InternalChildren.Count + Columns - 1) / Columns;

    protected override Size MeasureOverride(Size sizeAvailable)
    {
        var sizeChild = new Size(sizeAvailable.Width / Columns, sizeAvailable.Height / Rows);

        double maxwidth = 0;
        double maxheight = 0;

        foreach (UIElement child in InternalChildren)
        {
            child.Measure(sizeChild);

            maxwidth = Math.Max(maxwidth, child.DesiredSize.Width);
            maxheight = Math.Max(maxheight, child.DesiredSize.Height);
        }
        return new Size(Columns * maxwidth, Rows * maxheight);
    }

    protected override Size ArrangeOverride(Size sizeFinal)
    {
        var sizeChild = new Size(sizeFinal.Width / Columns, sizeFinal.Height / Rows);
        for (var index = 0; index < InternalChildren.Count; index++)
        {
            var row = index / Columns;
            var col = index % Columns;
            var rectChild = new Rect(new Point(col * sizeChild.Width, row * sizeChild.Height), sizeChild);

            InternalChildren[index].Arrange(rectChild);
        }
        return sizeFinal;
    }
}

XAML

<ListBox x:Name="MyListBox">
    <ListBox.ItemsPanel>
        <ItemsPanelTemplate>
            <uniformGridDemo:MyUniformGrid Columns="2" />
        </ItemsPanelTemplate>
    </ListBox.ItemsPanel>
</ListBox>

背后的代码

    public MainWindow()
    {
        InitializeComponent();
        var list = new List<int>();
        for (int i = 0; i < 1000; i++)
        {
            list.Add(i);
        }
        MyListBox.ItemsSource = list;
    }

谢谢

Answer 1

我不是VirtualizingStackPanel的专家，但如果你只想解决项目显示问题，下面就行了。

 public class MyUniformGrid :  VirtualizingStackPanel
{
    public static readonly DependencyProperty ColumnsProperty = DependencyProperty.Register("Columns", typeof(int), typeof(MyUniformGrid), new FrameworkPropertyMetadata(1, FrameworkPropertyMetadataOptions.AffectsMeasure));

    public int Columns
    {
        set { SetValue(ColumnsProperty, value); }
        get { return (int)GetValue(ColumnsProperty); }
    }

    private int Rows
    {
        get
        {                
            return (InternalChildren.Count + Columns - 1) / Columns;
        }
    }

    protected override Size MeasureOverride(Size sizeAvailable)
    {
        base.MeasureOverride(sizeAvailable);
        var sizeChild = new Size(sizeAvailable.Width / Columns, sizeAvailable.Height / Rows);

        double maxwidth = 0;
        double maxheight = 0;

        foreach (UIElement child in this.InternalChildren)
        {
            child.Measure(sizeChild);

            maxwidth = Math.Max(maxwidth, child.DesiredSize.Width);
            maxheight = Math.Max(maxheight, child.DesiredSize.Height);
        }
        return new Size(Columns * maxwidth, Rows * maxheight);

    }

    protected override Size ArrangeOverride(Size sizeFinal)
    {
        base.ArrangeOverride(sizeFinal);
        var sizeChild = new Size(sizeFinal.Width / Columns, sizeFinal.Height / Rows);
        for (var index = 0; index < InternalChildren.Count; index++)
        {
            var row = index / Columns;
            var col = index % Columns;
            var rectChild = new Rect(new Point(col * sizeChild.Width, row * sizeChild.Height), sizeChild);

            InternalChildren[index].Arrange(rectChild);
        }
        return sizeFinal;
    }
}

但是VirtualizingStackPanel是一个非常复杂的实现，然后是overriding MeasureOverride＆amp; ArrangeOverride方法和安排项目。你需要处理滚动信息并尊重那个添加＆amp;需要处理面板中的物品移除。因此，即使完全显示项目后，您也可能无法获得所需的性能。

Answer 2

我已经在Silverlight中实现了类似的功能，方法是将样式应用于ListBox并将ItemsPanelTemplate替换为WrapPanel。我在Windows Phone和WPF项目中使用了相同的内容，没有任何问题。

样式

<!--Wrapping ListBox Styles-->
<Style x:Key="StretchedItemContainerStyle" TargetType="ListBoxItem">
    <Setter Property="HorizontalContentAlignment" Value="Stretch" />
</Style>

<Style x:Key="ListBox_HorizontalWrapStyle" TargetType="ListBox">
    <Setter Property="ItemContainerStyle" Value="{StaticResource StretchedItemContainerStyle}"/>
    <Setter Property="ItemsPanel">
        <Setter.Value>
            <ItemsPanelTemplate>
                <WrapPanel Orientation="Horizontal" Margin="0"/>
            </ItemsPanelTemplate>
        </Setter.Value>
    </Setter>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="ListBox">
                <ScrollViewer VerticalScrollBarVisibility="Auto" BorderBrush="{x:Null}" >
                    <ItemsPresenter />
                </ScrollViewer>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>
<!--End Wrapping ListBox Styles-->

的Xaml

<ListBox x:Name="MyListBox" Style="StaticResource ListBox_HorizontalWrapStyle">

您还应该能够设定WrapPanel的样式，以便从中获得其他性能提升。

从VirtualizingStackPanel派生不起作用

2 个答案: