c# – 在WinRT / UWP中创建自定义虚拟化控件

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),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),new PropertyMetadata(
            null,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,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.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,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,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>