There are many way
But I prefer you use OnMouseClick event
use cursor property and find movement and change width
diff = oldx-cursor.position.x
GridView1.Columns[0].ItemStyle.Width = GridView1.Columns[0].ItemStyle.Width+diff;
In case of increasing width,
diff = 455-465 = 10;
then
GridView1.Columns[0].ItemStyle.Width = 50+10=60;
In case of decreasing width,
diff = 475-465 = -10;
then
GridView1.Columns[0].ItemStyle.Width = 50+(-10)=40;</pre>
Hope this will help
All the best