how to store grid cell value in text box

i m using the statement below to store value of grid cell into a text box . But (GridView1.Rows[i].Cells[4].Text) is displaying as null . plz any one tell me why'开发者_StackOverflow社区s this happening

Project_name.Text = GridView1.Rows[i].Cells[4].Text; 

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Make sure you're GridView1.Rows[i].RowType is a DataControlRowType.DataRow