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Question

我正在使用通用Windows平台构建Windows Phone 10应用程序。在我的应用程序中，我有一个标准的CalendarView，我希望在有事件的日期显示密度颜色。我们的想法是在加载页面后立即加载日历，发出API请求，并且在成功检索数据后，CalendarView会刷新它的UI以便调用CalendarViewDayItemChanging事件。从那里我可以为有事件的单元格设置密度颜色。

除了一部分，我几乎所有工作都正常。当日历首次加载时，我将其最小/最大日期范围设置为当前月份，这样我们一次只能看到一个月。这会导致日历的UI按预期刷新。但是，在我的API请求完成后，如果我尝试再次将最小/最大日期范围设置为相同的日期，则日历不会刷新它的UI。因此，我无法强制CalendarView刷新它的UI。

我尝试过调用UpdateLayout，我尝试重置最小/最大日期范围，并且我尝试将日历的DataContext绑定到我的代码中的ObservableCollection我的数据更新时更新。这些都不起作用，我没有看到任何方法来更新UI。

我对UWP很陌生，所以不确定我做错了什么。我知道数据绑定的概念是UWP的一个重要组成部分，但我不确定如何将我的数据绑定到此CalendarView，以便在刷新数据时刷新。有什么建议吗？

下面是我现在的代码的快速摘录。

XAML

<CalendarView 
    Name="Calendar"
    NumberOfWeeksInView="6"
    CalendarViewDayItemChanging="CalendarView_DayItemChanging"
    DataContext="{Binding CalendarDates}">
</CalendarView>

代码隐藏

namespace Pages
{
    public sealed partial class CalendarPage : BasePage
    {
        #region Private Variables

        private CalendarPageModel PageModel = new CalendarPageModel();
        private ObservableCollection<DateTime> CalendarDates;

        #endregion

        #region Constructor

        public CalendarPage()
        {
            this.InitializeComponent();
            CalendarDates = new ObservableCollection<DateTime>();
        }

        #endregion

        #region Events

        private void Page_Loaded(object sender, RoutedEventArgs args)
        {
            SetCalendarDateRange(); //NOTE: This is done here so that my UI consistantly shows the correct dates on the screen
            LoadData();
        }

        private void CalendarView_DayItemChanging(CalendarView sender, CalendarViewDayItemChangingEventArgs args)
        {
            if (!PageModel.DateHasEvent(args.Item.Date))
            {
                args.Item.SetDensityColors(null);
            }
            else
            {
                List<Color> colors = new List<Color>();
                Color? color = Application.Current.Resources["CalendarHasEventDensityColor"] as Color?;
                if (color != null)
                {
                    colors.Add((Color)color);
                }

                args.Item.SetDensityColors(colors);
            }
        }

        #endregion

        #region Data

        private void SetCalendarDateRange()
        {
            Calendar.MinDate = PageModel.StartDate;
            Calendar.MaxDate = PageModel.EndDate;
        }

        private async void LoadData()
        {
            // get data
            await PageModel.RefreshData(PageModel.StartDate, PageModel.EndDate);

            // force calendar to update
            //NOTE: This only works if the date range is actually different than what it's currently set to
            SetCalendarDateRange();

            //NOTE: I have tried to just manually add a date to my observable collection to see if it'll kick off the calendar refresh, but it doesn't
            CalendarDates.add(DateTime.Now);
        }

        #endregion
    }
}

Answer 1

坏消息
不幸的是，CalendarView控件是针对此方案设计的。由于它在显示大量天数时针对性能进行了优化，因此仅在加载单个日期时刷新UI。

...然而

好消息
可以修改控件以创建此行为，但需要一些工作。

基本原则是负责绘制“密度”颜色块并将它们绑定到可以通过绑定更新的内容。

作为此工作的一个示例，请将以下内容添加到页面

<Page.Resources>
    <local:ColorBrushConverter x:Key="BrushConverter" />
</Page.Resources>
<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
    <StackPanel>
        <CalendarView Name="Calendar"
                      DisplayMode="Month"
                      CalendarViewDayItemChanging="CalendarView_DayItemChanging"
                      >
            <CalendarView.CalendarViewDayItemStyle>
                <Style TargetType="CalendarViewDayItem" >
                    <Setter Property="Template">
                        <Setter.Value>
                            <ControlTemplate TargetType="CalendarViewDayItem">
                                <Grid Opacity="0.5">
                                    <Grid.RowDefinitions>
                                        <RowDefinition Height="*"/>
                                        <RowDefinition Height="*"/>
                                        <RowDefinition Height="*"/>
                                        <RowDefinition Height="*"/>
                                        <RowDefinition Height="*"/>
                                    </Grid.RowDefinitions>
                                    <Rectangle Grid.Row="0" Fill="{Binding FifthColor, Converter={StaticResource BrushConverter}}" />
                                    <Rectangle Grid.Row="1" Fill="{Binding FourthColor, Converter={StaticResource BrushConverter}}" />
                                    <Rectangle Grid.Row="2" Fill="{Binding ThirdColor, Converter={StaticResource BrushConverter}}" />
                                    <Rectangle Grid.Row="3" Fill="{Binding SecondColor, Converter={StaticResource BrushConverter}}" />
                                    <Rectangle Grid.Row="4" Fill="{Binding FirstColor, Converter={StaticResource BrushConverter}}" />
                                </Grid>
                            </ControlTemplate>
                        </Setter.Value>
                    </Setter>
                </Style>
            </CalendarView.CalendarViewDayItemStyle>
        </CalendarView>
        <Button Click="AddEventClicked">Add random event</Button>
    </StackPanel>
</Grid>

随附代码：

public sealed partial class MainPage : Page
{
    private MyViewModel ViewModel;

    private DateTime today;
    private DateTime minDate;
    private DateTimeOffset maxDate;

    public MainPage()
    {
        this.InitializeComponent();

        // Keep these for reference
        this.today = DateTime.Now.Date;
        this.minDate = new DateTime(today.Year, today.Month, 1);
        this.maxDate = minDate.AddMonths(1);

        // Create our viewmodel
        ViewModel = MyViewModel.Generate(minDate.Date, maxDate.Date);
        Calendar.MinDate = minDate;
        Calendar.MaxDate = maxDate;

        // Add data for the next three days - will be shown when page loads
        ViewModel.Dates[today.AddDays(1)].Add(Colors.Red);
        ViewModel.Dates[today.AddDays(2)].Add(Colors.Purple);
        ViewModel.Dates[today.AddDays(2)].Add(Colors.Blue);
        ViewModel.Dates[today.AddDays(3)].Add(Colors.Green);
    }

    private void CalendarView_DayItemChanging(CalendarView sender, CalendarViewDayItemChangingEventArgs args)
    {
        // When the DayItem in the calendar is loaded
        var itemDate = args?.Item?.Date.Date ?? DateTime.MinValue;

        if (ViewModel.Dates.ContainsKey(itemDate))
        {
            // Set the datacontext for our custom control
            // - Which does support 2way binding :)
            args.Item.DataContext = ViewModel.Dates[itemDate];
        }
    }

    private void AddEventClicked(object sender, RoutedEventArgs e)
    {
        var rand = new Random();
        var randomColor = Color.FromArgb(
                                         255,
                                         (byte) rand.Next(0, 254),
                                         (byte)rand.Next(0, 254),
                                         (byte)rand.Next(0, 254));

        var randomDay = rand.Next(1, 29);
        var randDateInMonth = new DateTime(today.Year, today.Month, randomDay);

        if (ViewModel.Dates.ContainsKey(randDateInMonth))
        {
            ViewModel.Dates[randDateInMonth].Add(randomColor);
        }
    }
}

public class MyViewModel
{
    // The VM really just holds this dictionary
    public Dictionary<DateTime, DensityColors> Dates { get; }

    private MyViewModel()
    {
        this.Dates = new Dictionary<DateTime, DensityColors>();
    }

    // Static constructor to limit the dates and populate dictionary
    public static MyViewModel Generate(DateTime minDate, DateTime maxDate)
    {
        var generated = new MyViewModel();

        for (var i = 0; i < (maxDate - minDate).TotalDays; i++)
        {
            generated.Dates.Add(minDate.AddDays(i), new DensityColors());
        }

        return generated;
    }
}

public class DensityColors : ObservableCollection<Color>, INotifyPropertyChanged
{
    // Properties that expose items in underlying OC
    public Color FirstColor => Items.Any() ? Items.First() : Colors.Transparent;
    public Color SecondColor => Items.Count > 1 ? Items.Skip(1).First() : Colors.Transparent;
    public Color ThirdColor => Items.Count > 2 ? Items.Skip(2).First() : Colors.Transparent;
    public Color FourthColor => Items.Count > 3 ? Items.Skip(3).First() : Colors.Transparent;
    public Color FifthColor => Items.Count > 4 ? Items.Skip(4).First() : Colors.Transparent;

    protected override void InsertItem(int index, Color item)
    {
        base.InsertItem(index, item);

        // Hacky forcing of updating UI for all properties
        OnPropertyChanged(nameof(FirstColor));
        OnPropertyChanged(nameof(SecondColor));
        OnPropertyChanged(nameof(ThirdColor));
        OnPropertyChanged(nameof(FourthColor));
        OnPropertyChanged(nameof(FifthColor));
    }

    public event PropertyChangedEventHandler PropertyChanged;

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

public class ColorBrushConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, string language)
    {
        if (value is Color)
        {
            return new SolidColorBrush((Color)value);
        }

        return value;
    }

    public object ConvertBack(object value, Type targetType, object parameter, string language)
    {
        throw new NotImplementedException();
    }
}

这仅限于每天5个条目（不像内置控件那样10个，不再被忽略），但应该让您了解如何实现您之后的内容或根据需要进行修改。