Question

I created a C# application and integrated an Access DB (with 3 populated tables).

Now I try to get data from the Access DB-tables to display it in a TextBox, but nothing is visible.

Thank you in advance.

UPDATE: namespace –> using System.Data.OleDb;

Here is the code:

    OleDbDataReader myReader;
    OleDbConnection myCon;
    OleDbCommand myQuery;

    public Form1()
    {
        InitializeComponent();
        myCon = new OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\Users\\UserName\\Desktop\\MyClubAdministration\\MyClubAdministrationDB.accdb;Persist Security Info=False;");
        myCon.Open();
        myQuery = new OleDbCommand("select * from Lid, Lidgeld, Lidmaatschap", myCon);
        myReader = myQuery.ExecuteReader();
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        textBox1.Text = myReader.GetInt32(0).ToString();
    }

Answer 1

You need to Read before GetInt32 on an OleDBDataReader

private void Form1_Load(object sender, EventArgs e)     
{         
    myReader.Read();
    textBox1.Text = myReader.GetInt32(0).ToString();     
} 

However this code is very error prone.
Try to isolate the database operarations in a private methods and call just from one point without splitting between constructor and form_load.

private void ReadFromDB()
{
    using(OleDbConnection myCon = new OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\Users\\UserName\\Desktop\\MyClubAdministration\\MyClubAdministrationDB.accdb;Persist Security Info=False;"))
    {
         myCon.Open();             
         OleDbCommand myQuery = new OleDbCommand("select * from Lid, Lidgeld, Lidmaatschap", myCon);
         OleDbDataReader myReader = myQuery.ExecuteReader();
         if(myReader.HasRows)
         {
              myReader.Read();
              textBox1.Text = myReader.GetInt32(0).ToString();
         }
    }
}

call that method after InitializeComponent();

As a side note, I will avoid the globals for the database operations. With connection pooling the performance cost to open and reopen a connection is really minimal, while the complexity of housecleaning grows exponentially.