在WinRT / UWP中创建自定义虚拟化控件

Question

在WPF中， FrameworkElement派生类可以通过AddVisualChild提供自己的子AddVisualChild 。 这样就可以实现自己的虚拟控件，只生成可见的子控件。 您也可以在没有支持集合的情况下生成子项。

我想使用这种技术从WPF到Windows 10 UWP移植几个控件，但目前还不清楚如何在WinRT UI中正确实现虚拟化。 因为在我对问题的原始版本的评论中说，询问实现技术对于Stack Overflow来说过于笼统我创建了一个简约的例子来解释我试图涵盖的关键特性，这些是

• 从数据模型动态生成子控件
• 为生成的子控件执行自定义布局逻辑

我做了以下考虑：

• 据我所知，自定义控件不可能像在WPF中那样管理自己的子节点
• 我排除了Panel子类，因为当我使用我的自定义控件时（由其他人使用），它很容易出错。 小组子项应该由包含XAML而不是小组控制。
• 我排除了ItemsControl子类，因为提供后备集合是不合理的（数据虚拟化是一项要求）

（请注意，排除它们可能是一个错误，所以如果是，请指出它。）

以下WPF代码创建无限滚动日期范围，但仅实现当前可见的单元格。 我故意保持它尽可能简约，所以它没有多大意义，但它确实提出了我上面提到的两个关键特性，我需要了解如何在WinRT中实现。

所以我的问题是：是否可以在WinRT中创建这样的控件，动态构建其子节点以显示无限滚动带？ 请记住，它需要是自包含的，以便放置在任意页面上，而页面不必包含额外的代码（否则它毕竟不是可重用的控件）。

如果你已经知道如何实现虚拟化并且可以给我一些提示，我认为它足以概述如何在WinRT中完成它。

WPF来源：

using System;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Media;

namespace Sandbox
{
    public class DateBand : FrameworkElement
    {
        public static readonly DependencyProperty ScrollOffsetProperty = DependencyProperty.Register(
            nameof(ScrollOffset), typeof(double), typeof(DateBand), new FrameworkPropertyMetadata {
                AffectsMeasure = true,
            });

        public double ScrollOffset
        {
            get { return (double)GetValue(ScrollOffsetProperty); }
            set { SetValue(ScrollOffsetProperty, value); }
        }

        public static readonly DependencyProperty CellTemplateProperty = DependencyProperty.Register(
            nameof(CellTemplate), typeof(DataTemplate), typeof(DateBand), new FrameworkPropertyMetadata {
                AffectsMeasure = true,
            });

        public DataTemplate CellTemplate
        {
            get { return (DataTemplate)GetValue(CellTemplateProperty); }
            set { SetValue(CellTemplateProperty, value); }
        }

        private List<DateCell> _cells = new List<DateCell>();
        private DateTime _startDate = new DateTime(DateTime.Today.Year, DateTime.Today.Month, 1);
        private const double cSlotWidth = 5;
        private const double cSlotHeight = 20;

        protected override int VisualChildrenCount => _cells.Count;
        protected override Visual GetVisualChild(int index) => _cells[index];

        protected override Size MeasureOverride(Size availableSize)
        {
            int usedCells = 0;
            double desiredWidth = 0;
            double desiredHeight = 0;

            if (!double.IsPositiveInfinity(availableSize.Height))
            {
                var index = (int)Math.Floor(ScrollOffset);
                var offset = (index - ScrollOffset) * cSlotHeight;

                while (offset < availableSize.Height)
                {
                    DateCell cell;
                    if (usedCells < _cells.Count)
                    {
                        cell = _cells[usedCells];
                    }
                    else
                    {
                        cell = new DateCell();
                        AddVisualChild(cell);
                        _cells.Add(cell);
                    }
                    usedCells++;

                    var cellValue = _startDate.AddMonths(index);
                    cell._offset = offset;
                    cell._width = DateTime.DaysInMonth(cellValue.Year, cellValue.Month) * cSlotWidth;
                    cell.Content = cellValue;
                    cell.ContentTemplate = CellTemplate;
                    cell.Measure(new Size(cell._width, cSlotHeight));

                    offset += cSlotHeight;
                    index++;

                    desiredHeight = Math.Max(desiredHeight, offset);
                    desiredWidth = Math.Max(desiredWidth, cell._width);
                }
            }

            if (usedCells < _cells.Count)
            {
                for (int i = usedCells; i < _cells.Count; i++)
                    RemoveVisualChild(_cells[i]);

                _cells.RemoveRange(usedCells, _cells.Count - usedCells);
            }

            return new Size(desiredWidth, desiredHeight);
        }

        protected override Size ArrangeOverride(Size finalSize)
        {
            foreach (var cell in _cells)
                cell.Arrange(new Rect(0, cell._offset, cell._width, cell.DesiredSize.Height));

            return finalSize;
        }
    }

    public class DateCell : ContentControl
    {
        internal double _offset;
        internal double _width;
    }

    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void Window_MouseWheel(object sender, MouseWheelEventArgs e)
        {
            Band.SetCurrentValue(DateBand.ScrollOffsetProperty, Band.ScrollOffset - e.Delta / Mouse.MouseWheelDeltaForOneLine);
        }
    }
}

WPF XAML：

<Window x:Class="Sandbox.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:Sandbox"
        MouseWheel="Window_MouseWheel">
    <DockPanel>
        <ScrollBar x:Name="Scroll" Orientation="Vertical" Minimum="-24" Maximum="+24" ViewportSize="6"/>
        <local:DateBand x:Name="Band" ScrollOffset="{Binding ElementName=Scroll, Path=Value, Mode=OneWay}">
            <local:DateBand.CellTemplate>
                <DataTemplate>
                    <Border BorderBrush="Black" BorderThickness="1" Padding="5,2">
                        <TextBlock Text="{Binding StringFormat='yyyy - MMMM'}"/>
                    </Border>
                </DataTemplate>
            </local:DateBand.CellTemplate>
        </local:DateBand>
    </DockPanel>
</Window>

Answer 1

根据评论中的要求，我发布了最终的解决方案。 我只想出了使用某种Panel子类的解决方案，所以我想出了将控件拆分为两部分的妥协，以避免控件的用户意外地弄乱子集合。

所以我实际上有两个主要的类，一个是暴露公共API（如依赖属性）和支持主题的Control子类，另一个是实现实际虚拟化的Panel子类。 两者都通过XAML模板链接，如果有人在预期控件之外使用它，Panel子类将拒绝执行任何工作。

完成后，虚拟化非常简单，并且与在WPF中执行此操作的方式没有太大差别 - 只需修改Panel的Children，例如在MeasureOverride中。

为了说明，我已将问题中的代码移植到UWP，如下所示：

UWP资料来源：

[TemplatePart(Name = PanelPartName, Type = typeof(DateBandPanel))]
public class DateBand : Control
{
    private const string PanelPartName = "CellPanel";

    public static readonly DependencyProperty ScrollOffsetProperty = DependencyProperty.Register(
        nameof(ScrollOffset), typeof(double), typeof(DateBand), new PropertyMetadata(
            (double)0, new PropertyChangedCallback((d, e) => ((DateBand)d).HandleScrollOffsetChanged(e))));

    private void HandleScrollOffsetChanged(DependencyPropertyChangedEventArgs e)
    {
        _panel?.InvalidateMeasure();
    }

    public double ScrollOffset
    {
        get { return (double)GetValue(ScrollOffsetProperty); }
        set { SetValue(ScrollOffsetProperty, value); }
    }

    public static readonly DependencyProperty CellTemplateProperty = DependencyProperty.Register(
        nameof(CellTemplate), typeof(DataTemplate), typeof(DateBand), new PropertyMetadata(
            null, new PropertyChangedCallback((d, e) => ((DateBand)d).HandleCellTemplateChanged(e))));

    private void HandleCellTemplateChanged(DependencyPropertyChangedEventArgs e)
    {
        _panel?.InvalidateMeasure();
    }

    public DataTemplate CellTemplate
    {
        get { return (DataTemplate)GetValue(CellTemplateProperty); }
        set { SetValue(CellTemplateProperty, value); }
    }

    private DateBandPanel _panel;

    public DateBand()
    {
        this.DefaultStyleKey = typeof(DateBand);
    }

    protected override void OnApplyTemplate()
    {
        if (_panel != null)
            _panel._band = null;

        base.OnApplyTemplate();

        _panel = GetTemplateChild(PanelPartName) as DateBandPanel;

        if (_panel != null)
            _panel._band = this;
    }
}

public class DateBandPanel : Panel
{
    internal DateBand _band;
    private List<DateCell> _cells = new List<DateCell>();
    private DateTime _startDate = new DateTime(DateTime.Today.Year, DateTime.Today.Month, 1);
    private const double cSlotWidth = 5;
    private const double cSlotHeight = 26;

    protected override Size MeasureOverride(Size availableSize)
    {
        int usedCells = 0;
        double desiredWidth = 0;
        double desiredHeight = 0;

        if (!double.IsPositiveInfinity(availableSize.Height) && _band != null)
        {
            var index = (int)Math.Floor(_band.ScrollOffset);
            var offset = (index - _band.ScrollOffset) * cSlotHeight;

            while (offset < availableSize.Height)
            {
                DateCell cell;
                if (usedCells < _cells.Count)
                {
                    cell = _cells[usedCells];
                }
                else
                {
                    cell = new DateCell();
                    Children.Add(cell);
                    _cells.Add(cell);
                }
                usedCells++;

                var cellValue = _startDate.AddMonths(index);
                cell._offset = offset;
                cell._width = DateTime.DaysInMonth(cellValue.Year, cellValue.Month) * cSlotWidth;
                cell.Content = new CellData(cellValue);
                cell.ContentTemplate = _band.CellTemplate;
                cell.Measure(new Size(cell._width, cSlotHeight));

                offset += cSlotHeight;
                index++;

                desiredHeight = Math.Max(desiredHeight, offset);
                desiredWidth = Math.Max(desiredWidth, cell._width);
            }
        }

        if (usedCells < _cells.Count)
        {
            for (int i = usedCells; i < _cells.Count; i++)
                Children.Remove(_cells[i]);

            _cells.RemoveRange(usedCells, _cells.Count - usedCells);
        }

        return new Size(desiredWidth, desiredHeight);
    }

    protected override Size ArrangeOverride(Size finalSize)
    {
        foreach (var cell in _cells)
            cell.Arrange(new Rect(0, cell._offset, cell._width, cell.DesiredSize.Height));

        return finalSize;
    }
}

public class CellData
{
    public DateTime Date { get; }
    public CellData(DateTime date) { this.Date = date; }
}

public class DateCell : ContentControl
{
    internal double _offset;
    internal double _width;
}

public class FormattingConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, string language)
    {
        if (value == null)
            return null;

        if (parameter == null)
            return value.ToString();

        return ((IFormattable)value).ToString((string)parameter, CultureInfo.CurrentCulture);
    }

    object IValueConverter.ConvertBack(object value, Type targetType, object parameter, string language)
    {
        throw new NotSupportedException();
    }
}

public sealed partial class MainPage : Page
{
    public MainPage()
    {
        this.InitializeComponent();
    }

    private void Page_PointerWheelChanged(object sender, PointerRoutedEventArgs e)
    {
        Scroll.Value -= e.GetCurrentPoint(this).Properties.MouseWheelDelta / 120.0;
    }
}

UWP XAML页面：

<Page x:Class="Sandbox.MainPage"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:local="using:Sandbox"
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
      mc:Ignorable="d"
      PointerWheelChanged="Page_PointerWheelChanged">
    <Page.Resources>
        <local:FormattingConverter x:Key="FormattingConverter"/>
    </Page.Resources>
    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="auto"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>
        <ScrollBar x:Name="Scroll" Grid.Column="0" Orientation="Vertical" IndicatorMode="MouseIndicator" Minimum="-24" Maximum="+24" ViewportSize="6"/>
        <local:DateBand x:Name="Band" Grid.Column="1" ScrollOffset="{Binding ElementName=Scroll, Path=Value, Mode=OneWay}">
            <local:DateBand.CellTemplate>
                <DataTemplate x:DataType="local:CellData">
                    <Border BorderBrush="Black" BorderThickness="1" Padding="5,2">
                        <TextBlock Text="{x:Bind Path=Date, Converter={StaticResource FormattingConverter}, ConverterParameter='yyyy - MMMM'}"/>
                    </Border>
                </DataTemplate>
            </local:DateBand.CellTemplate>
        </local:DateBand>
    </Grid>
</Page>

UWP XAML主题：

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:local="using:Sandbox">
    <Style TargetType="local:DateBand" >
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="local:DateBand">
                    <Border Background="{TemplateBinding Background}"
                            BorderBrush="{TemplateBinding BorderBrush}"
                            BorderThickness="{TemplateBinding BorderThickness}">
                        <local:DateBandPanel Name="CellPanel"/>
                    </Border>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>

Answer 2

我会选择TemplatedControl，你可以在XAML中定义你想要的控制结构，这将更容易，

当我在Codeplex上构建可视化图表库时，我做到了这一点