无法将对象从DBNull强制转换为其他类型

Question

我收到错误“对象无法从DBNull转换为其他类型”请帮助我，我是新手

public void GridView1_SelectedIndexChanged(object sender, EventArgs e)
    {
   int count = 0;
        SqlConnection con = new SqlConnection("server=ADMIN- PC\\SQLEXPRESS;initial catalog=content;integrated security=true");
        con.Open();
        SqlCommand cmd;
        cmd = new SqlCommand("select * from usrimg where ImageName='" + GridView1.SelectedDataKey["ImageName"].ToString() + "'", con);
        SqlDataReader dr = cmd.ExecuteReader();
        if (dr.Read())
        {

            count = Convert.ToInt16(dr[4]);//Error:Object cannot be cast from DBNull to other types 
            count++;
            dr.Close();
            cmd = new SqlCommand("update usrimg set [count] =" + count + "where ImageName='" + GridView1.SelectedDataKey["Image Name"].ToString() + ")", con);
            cmd.ExecuteNonQuery();
            con.Close();
        }

Answer 1

我相信你表中的那个位置有一个空值。在尝试转换它之前，请确保它不为空。

if(!Convert.IsDBNull(dr[4]))
{
count = Convert.ToInt16(dr[4]);
//whatever you need done with the count in here...
}