c＃DB列值

Question

     MySqlConnection con = new MySqlConnection("host=db4free.net;user=*;password=*;database=*;");
    MySqlCommand xcmd = new MySqlCommand("SELECT x FROM members WHERE id='" + Login.idd + "';");
      xcmd.Connection = con;
        xint.Connection = con;
        DataTable dt = new DataTable();
        con.Open();
        xcmd.ExecuteNonQuery();
        int xx = (int)xcmd.ExecuteScalar();
        xcmd.Connection.Close();;
        xcmd.Dispose();
        x = xx;
        con.Close();
        if (x == 2)
        {
            button6.BackgroundImage = Properties.Resources.logo;
        }

I want the program to read the value of X from the database, add it in a variable and then if it is equal to 2 to show the logo...

Answer 1

Use ExecuteScalar , it's much more straight forward:

MySqlConnection con = new MySqlConnection("host=db4free.net;user=*;password=*;database=*;");
MySqlCommand xcmd = new MySqlCommand("SELECT x FROM members WHERE id='" + Login.idd + "';", con);

con.Open();
var x = (int)xcmd.ExecuteScalar();
con.Close();
if (x == 2)
{
    button6.BackgroundImage = Properties.Resources.logo;
}

further, please take note to the answer provided by dash . I generally add that to my answers, and was in the process, but saw his addition.

And a note about setting a BackgroundImage -you need to work with the Layout and Size . The following code is from MSDN:

// Specify the layout style of the background image. Tile is the default.
button1.BackgroundImageLayout = ImageLayout.Center;

// Make the button the same size as the image.
button1.Size = button1.BackgroundImage.Size;

those settings above may not be right based on your image.

Answer 2

In your original code, you have some bits you don't need; for example, the DataTable, the xint command, and the ExecuteNonQuery (which is for doing stuff which only updates/inserts/deletes from the database, for example, and doesn't return results)

using(MySqlConnection con = new MySqlConnection("host=db4free.net;user=*;password=*;database=*;"))
{
    using(MySqlCommand xcmd = new MySqlCommand("SELECT x FROM members WHERE id=@loginid;"))
    {
        xcmd.connection = con;
        xcmd.Parameters.AddWithValue("@loginid", Login.idd);
        con.Open();
        int x = Convert.ToInt32(xcmd.ExecuteScalar());
        //Do something with x
        if(x == 2)
        {
            button6.BackgroundImage = Properties.Resources.logo;
        }
    }
}

If you are going to be doing this style of data access, I would recommend parameterizing your query, and using the ' using ' statement.

The first will help prevent SQL Injection attacks, while the second will ensure non-managed resources are disposed of when you leave the scope of the various blocks.