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tb.SelectionStart = 0;
tb.SelectionLength = tb.Text.Length;
try
tb.SelectAll();
this.gridDataBoundGrid1.ActivateCurrentCellBehavior = GridCellActivateAction.SelectAll;
But this will select all whether you click the cell or move with the cursor keys. To only do it whne you click, use your code above, but also add e.Cancel = true. Without this, the grid continues to process the click which will do whatever the ActivateCurrentCellBehavior indicates.