Problem with string array?

Question

I have a problem with this code, because it gives me following error message

Object reference not set to an instance of an object when I use the line

values[countValues] = reader2.GetString("textinfo"); in the code below

Can someone help me?

public static string[] values;
int countValues = 0;
using(var connection = new MySqlConnection(connString))
{
    connection.Open();
    string query = "select * from showvalues where idvalue = '" + idStatus + "'";
    using(var command2 = new MySqlCommand(query, connection))
    {
        using(var reader2 = command2.ExecuteReader())
        {
            while(reader2.Read())
            {
                listBoxMeasurement.Items.Add(reader2.GetString("textinfo"));
                values[countValues] = reader2.GetString("textinfo");
                countValues++;
            }
            countValues = 0;
            connection.Close();
        }
    }
}

Answer 1

Hi @Ken Ekholm , Welcome to Microsoft Q&A.

Your error is because you only declared the array but didn't initialize it.

You can use List<string> instead of Array.

If you need an array, just use string[] values = valuesList.ToArray(); to get the array at the end, and the declaration of this values can also be placed before the database using for global use.

Use parameterized queries to avoid sql injection.

using (var connection = new MySqlConnection(connString))
{
    connection.Open();
    string query = "SELECT * FROM showvalues WHERE idvalue = @idStatus";
    using (var command2 = new MySqlCommand(query, connection))
    {
        command2.Parameters.AddWithValue("@idStatus", idStatus);
        
        using (var reader2 = command2.ExecuteReader())
        {
            List<string> valuesList = new List<string>();

            while (reader2.Read())
            {
                listBoxMeasurement.Items.Add(reader2.GetString("textinfo"));
                valuesList.Add(reader2.GetString("textinfo"));
            }

            string[] values = valuesList.ToArray();
            connection.Close();
        }
    }
}

Best Regards,

Jiale

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Answer 2

Arrays in c# are not dynamic. You declared an empty array, but try to set a value. Not sure why it is not subscript out of range.

also your sql allows sql injection, and should be fixed.