asp.net（C#）并非所有的代码路径都返回值

    public bool IsExist(string artNo1)
    {
        string artNo;
        List<string> list_artNo = new List<string>();

        foreach (GridViewRow rows in GridView1.Rows)
        {
            artNo = rows.Cells[0].Text;
            list_artNo.Add(artNo);
        }
        foreach (string item in list_artNo)
        {
            if (item==artNo1.ToString())
            {
                return true;
            }
            if (item != artNo1.ToString())
            {
                return false;
            }
        }
    }

这代码写的。。。本来一句话的事，你balabala写了这么多行：

   public bool IsExist(string artNo1)
    {
            return GridView1.Rows.Cast<GridViewRow>().Any(x=>x.Cells[2].Text==artNo1.ToString());
    }

foreach (string item in list_artNo)
{
return ( item==artNo1.ToString())
}

   public bool IsExist(string artNo1)
    {
            return GridView1.Rows.Cast<GridViewRow>().Any(x=>x.Cells[0].Text==artNo1.ToString());
    }

 public bool IsExist(string artNo1)
    {
        string artNo;
        List<string> list_artNo = new List<string>();

        foreach (GridViewRow rows in GridView1.Rows)
        {
            artNo = rows.Cells[0].Text;
            list_artNo.Add(artNo);
        }
        foreach (string item in list_artNo)
        {
            if (item==artNo1.ToString())
            {
                return true;
            }
            if (item != artNo1.ToString())
            {
                return false;
            }
        }
                return false;//////////
    }