点击girdview中的编辑按钮就会报错：输入字符串的格式不正确。

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protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
int i;
for (i = 0; i < GridView1.Rows.Count; i++)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
e.Row.Attributes.Add("onmouseover", "c=this.style.backgroundColor;this.style.backgroundColor='#00A9FF'");
e.Row.Attributes.Add("onmouseout", "this.style.backgroundColor=c");
}
}
}

protected void GridView1_DataBound(object sender, EventArgs e)
{
    double value = 0;
        foreach(GridViewRow row in GridView1.Rows)
        {
            double price = Convert.ToDouble(row.Cells[3].Text);
            int count = Convert.ToInt32(row.Cells[5].Text);
            value += price * count;
        }
    GridViewRow footer = GridView1.FooterRow;
    footer.Cells[0].ColumnSpan = 5;
    footer.Cells[0].HorizontalAlign = HorizontalAlign.Center;
    footer.Cells.RemoveAt(4);

    footer.Cells[0].Text = "库存总价为（元）：" + value;





    以上是我的代码，报错在  double price = Convert.ToDouble(row.Cells[3].Text);这句上，