CODEWITHSUNDEEP
c#c#-4.0
Aravind Sai
Aravind Sai

Reputation: 99

C# command execution error for data reader

While I am running the code below, the compiler is giving me the error: "object reference not set to an instance of an object". Please can you tell what mistakes I have made in this code.

   public void text()
        {
            cn1.Open();
            string s;
//error came here
            s = "select Request_Type from dbo.component where Material_Code='" +
Mcodeddl.SelectedItem.Text + "' ";
//end

            SqlCommand cd1 = new SqlCommand(s, cn1);
            SqlDataReader rd;
            try
            {
                rd = cd1.ExecuteReader();
                while (rd.Read())
                {
                    TextBox4.Text = rd["Request_Type"].ToString().Trim();
                }
                rd.Close();

            }
            catch (Exception e)
            {
                Response.Write(e.Message);
            }
            finally
            {
                cd1.Dispose();
                cn1.Close();
            }
        }

Upvotes: 2

Views: 166

Answers (2)

Damith
Damith

Reputation: 63105

var code = Mcodeddl.SelectedItem.Text; // you may need to check Mcodeddl.SelectedItem != null here, if you not set default selected item 

if (string.IsNullOrEmpty(code)) return; // return if code type empty, or show message. depending on your requirement

using (SqlConnection connection = new SqlConnection(connectionString)) // using statement will dispose connection automatically
{
    connection.Open();

    using (SqlCommand command = new SqlCommand("select Request_Type from dbo.component where Material_Code= @MaterialCode", connection))
    {
        command.Parameters.AddWithValue("@MaterialCode", code); // use parameters 

        SqlDataReader reader = command.ExecuteReader();
        while (reader.Read())
        {
            var request = reader["Request_Type"];
            TextBox4.Text = request != DBNull.Value ? request.ToString().Trim() :string.Empty;// check null before ToString
        }
    }
}
}
catch (Exception e)
{
Response.Write(e.Message);
}

Upvotes: 1

JohnFx
JohnFx

Reputation: 34907

Just a hunch, but either Mcodeddl or Mcodeddl.SelectedItem is null.

There is probably no selected item in the (assuming) dropdown control.

Add a null check on the Mcodeddl.SelectedItem object before the code with the error to prevent that from happening.

Upvotes: 1

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