Oledb连接字符串未初始化

本文关键字：初始化 字符串 连接 Oledb | 更新日期: 2023-09-27 18:01:48

    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，抱歉伙计们又问这个问题了，但是我已经试了三个小时了，挥舞着白旗。仍然得到相同的错误

我只想从数据库中选择的余额值显示在标签中。

> & lt;感谢

Oledb连接字符串未初始化

您没有将连接与命令对象关联:

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

注意，重用连接并不总是最好的设计。连接是在。net中池化的，因此重新创建它们通常不是一个昂贵的操作。一个更好的设计是将连接字符串存储为一个类属性，然后在需要的时候创建一个连接:

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

使用时:

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
    }
}
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