DataGridBoolColumn Class

using System;
using System.Data;
using System.Windows.Forms;
using System.Drawing;
using System.ComponentModel;

public class MyForm : Form 
{
    private DataTable myTable;
    private DataGrid myGrid = new DataGrid();

    public MyForm() : base() 
    {
        try
        {
            InitializeComponent();

            myTable = new DataTable("NamesTable");
            myTable.Columns.Add(new DataColumn("Name"));
            DataColumn column = new DataColumn
                ("id", typeof(System.Int32));
            myTable.Columns.Add(column);
            myTable.Columns.Add(new 
                DataColumn("calculatedField", typeof(bool)));
            DataSet namesDataSet = new DataSet();
            namesDataSet.Tables.Add(myTable);
            myGrid.SetDataBinding(namesDataSet, "NamesTable");

            AddTableStyle();
            AddData();
        }
        catch (System.Exception exc)
        {
            Console.WriteLine(exc.ToString());
        }
    }


    private void grid_Enter(object sender, EventArgs e) 
    {
        myGrid.CurrentCell = new DataGridCell(2,2);
    }

    private void AddTableStyle()
    {
        // Map a new  TableStyle to the DataTable. Then  
        // add DataGridColumnStyle objects to the collection 
        // of column styles with appropriate mappings.
        DataGridTableStyle dgt = new DataGridTableStyle();
        dgt.MappingName = "NamesTable";

        DataGridTextBoxColumn dgtbc = new DataGridTextBoxColumn();
        dgtbc.MappingName = "Name";
        dgtbc.HeaderText= "Name";
        dgt.GridColumnStyles.Add(dgtbc);

        dgtbc = new DataGridTextBoxColumn();
        dgtbc.MappingName = "id";
        dgtbc.HeaderText= "id";
        dgt.GridColumnStyles.Add(dgtbc);

        DataGridBoolColumnInherit db = 
            new DataGridBoolColumnInherit();
        db.HeaderText= "less than 1000 = blue";
        db.Width= 150;
        db.MappingName = "calculatedField";
        dgt.GridColumnStyles.Add(db);

        myGrid.TableStyles.Add(dgt);

        // This expression instructs the grid to change 
        // the color of the inherited DataGridBoolColumn 
        // according to the value of the id field. If it's 
        // less than 1000, the row is blue. Otherwise, 
        // the color is yellow.
        db.Expression = "id < 1000";
    }

    private void AddData() 
    {
        // Add data with varying numbers for the id field. 
        // If the number is over 1000, the cell will paint 
        // yellow. Otherwise, it will be blue.
        DataRow dRow = myTable.NewRow();

        dRow["Name"] = "name 1 ";
        dRow["id"] = 999;
        myTable.Rows.Add(dRow);

        dRow = myTable.NewRow();
        dRow["Name"] = "name 2";
        dRow["id"] = 2300;
        myTable.Rows.Add(dRow);

        dRow = myTable.NewRow();
        dRow["Name"] = "name 3";
        dRow["id"] = 120;
        myTable.Rows.Add(dRow);

        dRow = myTable.NewRow();
        dRow["Name"] = "name 4";
        dRow["id"] = 4023;
        myTable.Rows.Add(dRow);

        dRow = myTable.NewRow();
        dRow["Name"] = "name 5";
        dRow["id"] = 2345;
        myTable.Rows.Add(dRow);

        myTable.AcceptChanges();
    }

    private void InitializeComponent() 
    {
        this.Size = new Size(500, 500);
        myGrid.Size = new Size(350, 250);
        myGrid.TabStop = true;
        myGrid.TabIndex = 1;

        this.StartPosition = FormStartPosition.CenterScreen;
        this.Controls.Add(myGrid);
      }
    [STAThread]
    public static void Main() 
    {
        Application.Run(new MyForm());
    }
}

public class DataGridBoolColumnInherit : DataGridBoolColumn 
{
    private SolidBrush trueBrush = Brushes.Blue as SolidBrush;
    private SolidBrush falseBrush = Brushes.Yellow as SolidBrush;
    private DataColumn expressionColumn = null;
    private static int count = 0;

    public Color FalseColor 
    {
        get 
        {
            return falseBrush.Color;
        }
        set 
        {
            falseBrush = new SolidBrush(value);
            Invalidate();
        }
    }

    public Color TrueColor 
    {
        get 
        {
            return trueBrush.Color;
        }
        set 
        {
            trueBrush = new SolidBrush(value);
            Invalidate();
        }
    }

    public DataGridBoolColumnInherit() : base () 
    {
        count ++;
    }


    // This will work only with a DataSet or DataTable. 
    // The code is not compatible with IBindingList implementations. 
    public string Expression 
    {
        get 
        {
            return this.expressionColumn == null ? String.Empty : 
                this.expressionColumn.Expression;
        }
        set 
        {
            if (expressionColumn == null)
                AddExpressionColumn(value);
            else 
                expressionColumn.Expression = value;
            if (expressionColumn != null && 
                expressionColumn.Expression.Equals(value))
                return;
            Invalidate();
        }
    }

    private void AddExpressionColumn(string value) 
    {
        // Get the grid's data source. First check for a null  
        // table or data grid. 
        if (this.DataGridTableStyle == null || 
            this.DataGridTableStyle.DataGrid == null)
            return;

        DataGrid myGrid = this.DataGridTableStyle.DataGrid;
        DataView myDataView = ((CurrencyManager) 
            myGrid.BindingContext[myGrid.DataSource, 
            myGrid.DataMember]).List 
            as DataView;

        // This works only with System.Data.DataTable. 
        if (myDataView == null)
            return;

        // If the user already added a column with the name  
        // then exit. Otherwise, add the column and set the  
        // expression to the value passed to this function.
        DataColumn col = myDataView.Table.Columns["__Computed__Column__"];
        if (col != null)
            return;
        col = new DataColumn("__Computed__Column__" + count.ToString());

        myDataView.Table.Columns.Add(col);
        col.Expression = value;
        expressionColumn = col;
    }

    // override the OnPaint method to paint the cell based on the expression. 
    protected override void Paint(Graphics g, Rectangle bounds,
        CurrencyManager source, int rowNum,
        Brush backBrush, Brush foreBrush,
        bool alignToRight) 
    {
        bool trueExpression = false;
        bool hasExpression = false;
        DataRowView drv = source.List[rowNum] as DataRowView;

        hasExpression = this.expressionColumn != null && 
            this.expressionColumn.Expression != null && 
            !this.expressionColumn.Expression.Equals(String.Empty);

        Console.WriteLine(string.Format("hasExpressionValue {0}",hasExpression));
        // Get the value from the expression column. 
        // For simplicity, we assume a True/False value for the  
        // expression column. 
        if (hasExpression) 
        {
            object expr = drv.Row[expressionColumn.ColumnName];
            trueExpression = expr.Equals("True");
        }

        // Let the DataGridBoolColumn do the painting. 
        if (!hasExpression)
            base.Paint(g, bounds, source, rowNum, 
                backBrush, foreBrush, alignToRight);

        // Paint using the expression color for true or false, as calculated. 
        if (trueExpression)
            base.Paint(g, bounds, source, rowNum, 
                trueBrush, foreBrush, alignToRight);
        else 
            base.Paint(g, bounds, source, rowNum, 
                falseBrush, foreBrush, alignToRight);
    }
}