Question

    namespace PCMS
    {
     public partial class frmPlayerInterface : Form
    {
        private OleDbConnection con = new OleDbConnection();
        OleDbCommand com = new OleDbCommand();
        private DataTable dt = new DataTable();
    public frmPlayerInterface(string getUser)
    {
        InitializeComponent();
        con.ConnectionString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\Projects\SDP\PCMS\SDP.accdb";
        lblUser.Text = getUser;
    }

    private void btnEnquire_Click(object sender, EventArgs e)
    {
        frmEnquire frmenq = new frmEnquire();
        frmenq.ShowDialog();

    }

    private void btnTopUp1_Click(object sender, EventArgs e)
    {
        frmTopUp frmTU = new frmTopUp();
        frmTU.ShowDialog();
    }

    private void frmPlayerInterface_Load(object sender, EventArgs e)
    {
        con.Open();
        OleDbCommand comm = new OleDbCommand();

        String sql = "select Balance from PlayerAccount where Player_User=@user";
        comm.Parameters.Add(new OleDbParameter("user", lblUser.Text));
        comm.CommandText = sql;

        OleDbDataReader cursor = comm.ExecuteReader();
        while (cursor.Read())
        {

            lblBalance.Text = cursor["Balance"].ToString();
        }
        con.Close();



    }





}

}

嘿抱歉的人再次问这个问题，但是我在过去的三个小时里一直试着这个并挥动白旗。仍然得到同样的错误。

我只想让数据库中选定的余额值显示在标签中。

谢谢＆gt;＆lt;

Answer 1

您没有将连接与命令对象关联起来：

    con.Open();
    String sql = "select Balance from PlayerAccount where Player_User=@user";
    OleDbCommand comm = new OleDbCommand(sql, con);

请注意，重复使用连接并不总是最佳设计。连接在.NET中汇集，因此重新创建它们通常不是一项昂贵的操作。更好的设计是将连接字符串存储为类属性，然后在需要时创建连接：

private string ConnectionString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\Projects\SDP\PCMS\SDP.accdb";  
// or better yet - pull form app.config...

当你使用它时：

String sql = "select Balance from PlayerAccount where Player_User=@user";
using(OleDbConnection con = new OleDbConnection(ConnectionString))
{
    con.Open();
    using(OleDbCommand comm = new OleDbCommand(sql, con))
    {
        ... Add parameters, execute query, return results
    }
}

oledb连接字符串未初始化

1 个答案: