Windows Forms FAQ resources

5. Windows Forms Datagrid

5.38 How can I get celltips or tooltips to vary from cell to cell in my DataGrid?

One way to do this is to use a ToolTip control and reset the control text as the mouse moves from cell to cell. Below is a derived DataGrid class that implements this idea. The main points are:

Have members that track the current hitRow and hitCol where the mouse is.
In a MouseMove handler, do a HitTest on the mouse location to see if there is a new hit cell. If so, set the hitRow & hitCol, and hook the tooltip to hold your text according to the cell. In our sample, we just display the string value of the grid cell.
Finally, in the MouseMove handler, after setting a new text in the tooltip, set the tooltip active so it can show itself in due time.

public class DataGridCellTips : DataGrid

{

private int hitRow;

private int hitCol;

private System.Windows.Forms.ToolTip toolTip1;

public DataGridCellTips()

{

hitRow = -1;

hitCol = -1;

this.toolTip1 = new System.Windows.Forms.ToolTip();

this.toolTip1.InitialDelay = 1000;

this.MouseMove += new MouseEventHandler(HandleMouseMove);

}

private void HandleMouseMove(object sender, MouseEventArgs e)

{

DataGrid.HitTestInfo hti = this.HitTest(new Point(e.X, e.Y));

if(hti.Type == DataGrid.HitTestType.Cell

&& ( hti.Row != hitRow || hti.Column != hitCol) )

{ //new hit row

hitRow = hti.Row;

hitCol = hti.Column;

if(this.toolTip1 != null && this.toolTip1.Active)

this.toolTip1.Active = false; //turn it off

this.toolTip1.SetToolTip(this, this[hitRow, hitCol].ToString());

this.toolTip1.Active = true; //make it active so it can show itself

//Console.WriteLine("MouseMove "+ hitRow.ToString() + " " + hitCol.ToString());

}