C# изменить цвет ячейки сетки данных

Я создал новый образец с некоторыми данными: вам нужно использовать конвертер с мультипривязкой, чтобы делать то, что вы хотите.

mainwindows.xaml:

<Window x:Class = "WpfApplication1.MainWindow"
        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:WpfApplication1 = "clr-namespace:WpfApplication1"
        xmlns:mc = "http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local = "clr-namespace:WpfApplication1"
        mc:Ignorable = "d"

        Title = "MainWindow" Height = "350" Width = "525">
    <Window.Resources>
        <WpfApplication1:HighlighterConverter x:Key = "myHighlighterConverter" />
    </Window.Resources>
    <Grid>
        <DataGrid x:Name = "arcad_Grid" Loaded = "arcad_Grid_Loaded" SelectionChanged = "arcad_Grid_SelectionChanged" 
                  AutoGenerateColumns = "True" SelectionUnit = "Cell" >
            <DataGrid.CellStyle>
                <Style TargetType = "{x:Type DataGridCell}">
                    <Setter Property = "Background">
                        <Setter.Value>
                            <MultiBinding Converter = "{StaticResource myHighlighterConverter}" >
                                <MultiBinding.Bindings>
                                    <Binding RelativeSource = "{RelativeSource Self}"></Binding>
                                    <Binding Path = "Row"></Binding>
                                </MultiBinding.Bindings>
                            </MultiBinding>
                        </Setter.Value>
                    </Setter>
                </Style>
            </DataGrid.CellStyle>
        </DataGrid>
    </Grid>
</Window>

во время загруженного события в mainwindow.xaml.cs:

    private void arcad_Grid_Loaded(object sender, RoutedEventArgs e)
    {
        DataTable table = new DataTable();
        table.Columns.Add("Dosage", typeof(int));
        table.Columns.Add("Drug", typeof(string));
        table.Columns.Add("Patient", typeof(string));
        table.Columns.Add("Color", typeof(string));

        // Here we add five DataRows.
        table.Rows.Add(25, "Indocin", "David", "rouge");
        table.Rows.Add(50, "Enebrel", "Sam", "vert");
        table.Rows.Add(10, "Hydralazine", "Christoff", "rouge");
        table.Rows.Add(21, "Combivent", "Janet", "vert");
        table.Rows.Add(100, "Dilantin", "Melanie", "vert");         

        arcad_Grid.ItemsSource = table.DefaultView;
    }

конвертер.cs:

using System;
using System.Data;
using System.Globalization;
using System.Windows;
using System.Windows.Data;
using System.Windows.Media;
using System.Windows.Controls;

namespace WpfApplication1
{
    public class HighlighterConverter : IMultiValueConverter
    {
        public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
        {
            if (values[1] is DataRow)
            {
                var cell = (DataGridCell)values[0];
                var row = (DataRow)values[1];
                var columnName = cell.Column.SortMemberPath;

                if (row[columnName].ToString() == "rouge" )
                    return Brushes.Red;
                if (row[columnName].ToString() == "vert")
                    return Brushes.Green;

            }
            return SystemColors.AppWorkspaceColor;
        }

        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
        {
            throw new System.NotImplementedException();
        }
    }

}

Другое решение с простым конвертером: вы добавляете это в convert.cs

public class ValueToBrushConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        string input;
        try
        {
            DataGridCell dgc = (DataGridCell)value;
            System.Data.DataRowView rowView = (System.Data.DataRowView)dgc.DataContext;
            input = (string)rowView.Row.ItemArray[dgc.Column.DisplayIndex];
        }
        catch (InvalidCastException e)
        {
            return DependencyProperty.UnsetValue;
        }
        switch (input)
        {
            case "rouge": return Brushes.Red;
            case "vert": return Brushes.Green;
            default: return DependencyProperty.UnsetValue;
        }
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotSupportedException();
    }
}

модификация в mainwindow.xaml:

<Window.Resources>
    <WpfApplication1:ValueToBrushConverter x:Key = "ValueToBrushConverter"/>
    <Style x:Key = "CellStyle" TargetType = "DataGridCell">
        <Setter Property = "Background" Value = "{Binding RelativeSource = {RelativeSource Self}, Converter = {StaticResource ValueToBrushConverter}}" />
    </Style>
</Window.Resources>
<Grid>
    <DataGrid x:Name = "arcad_Grid" Loaded = "arcad_Grid_Loaded" SelectionChanged = "arcad_Grid_SelectionChanged" 
              AutoGenerateColumns = "True" SelectionUnit = "Cell" CellStyle = "{StaticResource CellStyle}" >           
    </DataGrid>
</Grid>

тот же результат с меньшим кодированием