Question

Assume I have a class that looks like this:

class Sample
{
    public string Value { get; set; }
    public DateTime Begin { get; set; }
    public DateTime End { get; set; }
}

I want to display a list of Sample instances where each one changes color when the current time passes Begin and then changes color again when the current time passes End.

For example, say I have a DataGrid containing a Sample sort of like this:

dataGrid1.ItemsSource = new List<Sample> {
    { Value="123",
      Begin=DateTime.Parse("10:00"),
      End=DateTime.Parse("11:00") } };

How would I get the row showing “123” to be red at 9:59, turn yellow at 10:00, and turn red at 11:00?

EDIT: One thing I’m particularly concerned about is a timer explosion. If I have 10,000 Samples, will it be a problem to have 10k (or 20k) timers? What if I have 1M Samples? I think it might be a better idea to make the timers per grid row rather than per Sample.

Answer 1

By doing this:

MainPage.xaml

<UserControl xmlns:data="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Data"  x:Class="ColorGridRow.MainPage"
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" xmlns:local="clr-namespace:ColorGridRow" mc:Ignorable="d" d:DesignWidth="640" d:DesignHeight="480">
<Grid x:Name="LayoutRoot">
    <data:DataGrid ItemsSource="{Binding}" AutoGenerateColumns="False">
        <data:DataGrid.Columns>
            <data:DataGridTemplateColumn>
                <data:DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <Grid Background="{Binding RowBackground}">
                            <TextBlock Text="{Binding Value}"/>
                        </Grid>
                    </DataTemplate>
                </data:DataGridTemplateColumn.CellTemplate>
            </data:DataGridTemplateColumn>
            <data:DataGridTemplateColumn>
                <data:DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <Grid Background="{Binding RowBackground}">
                            <TextBlock Text="{Binding Begin}"/>
                        </Grid>
                    </DataTemplate>
                </data:DataGridTemplateColumn.CellTemplate>
            </data:DataGridTemplateColumn>
            <data:DataGridTemplateColumn>
                <data:DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <Grid Background="{Binding RowBackground}">
                            <TextBlock Text="{Binding End}"/>
                        </Grid>
                    </DataTemplate>
                </data:DataGridTemplateColumn.CellTemplate>
            </data:DataGridTemplateColumn>
        </data:DataGrid.Columns>
    </data:DataGrid>
</Grid>

MainPage.xaml.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Windows.Controls;
using System.Windows.Media;

namespace ColorGridRow
{
    public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();
            DataContext = new List<Sample>
                {
                    new Sample("1", DateTime.Now + TimeSpan.FromSeconds(1), DateTime.Now + TimeSpan.FromSeconds(3)),
                    new Sample("2", DateTime.Now + TimeSpan.FromSeconds(2), DateTime.Now + TimeSpan.FromSeconds(4)),
                    new Sample("3", DateTime.Now + TimeSpan.FromSeconds(3), DateTime.Now + TimeSpan.FromSeconds(5)),
                };
        }
    }

    public class Sample : INotifyPropertyChanged
    {
        private SolidColorBrush _savedRowBackground;
        private SolidColorBrush _rowBackground;

        public string Value { get; private set; }
        public DateTime Begin { get; private set; }
        public DateTime End { get; private set; }

        public SolidColorBrush RowBackground
        {
            get { return _rowBackground; }    
            set
            {
                _rowBackground = value;
                NotifyPropertyChanged("RowBackground");
            }
        }

        public event PropertyChangedEventHandler PropertyChanged = delegate { };

        private void NotifyPropertyChanged(string propertyName)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }

        public Sample(string value, DateTime begin, DateTime end)
        {
            Value = value;
            Begin = begin;
            End = end;
            RowBackground = new SolidColorBrush(Colors.Red);

            Observable.Timer(new DateTimeOffset(begin)).Subscribe(_ =>
            {
                _savedRowBackground = _rowBackground;
                RowBackground = new SolidColorBrush(Colors.Yellow);
            });

            Observable.Timer(new DateTimeOffset(end)).Subscribe(_ => RowBackground = _savedRowBackground);

        }
    }
}