Visual Studio 和 SQL 错误连接未关闭。连接的当前状态是打开的

Question

每当我单击添加按钮时，它都会告诉我错误 "The connection was not closed. The connection's current state is open."。我是 Visual Studio 2010 和 Sql Server 2008 的新手，帮助或任何建议都可以。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;

namespace MRP.SupplierMaterial
{
    public partial class Add : Form
    {

        SqlConnection con = new SqlConnection(Helper.GetCon());

        public Add()
        {
            InitializeComponent();
        }

       void GetSuppliers()
        {
            con.Open();
            SqlCommand cmd = new SqlCommand();
            cmd.Connection = con;
            cmd.CommandText = "SELECT CompanyName, ContactPerson, Phone, Mobile, Status, DateAdded, DateModified FROM Suppliers";
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataSet ds = new System.Data.DataSet();
            da.Fill(ds, "Suppliers");
            cmbSupplierID.DataSource = ds.Tables["Suppliers"];
            cmbSupplierID.DisplayMember = "CompanyName";
            cmbSupplierID.ValueMember = "SupplierID";
            con.Close();
        }

       void GetMaterials()
       {
           con.Open();
           SqlCommand cmd = new SqlCommand();
           cmd.Connection = con;
           cmd.CommandText = "SELECT Materials.MaterialID, " +
               "Materials.Name + ' (' + UnitID.UnitMeasure + ')' AS MaterialName " +
               "FROM Materials INNER JOIN UnitID ON Materials.UnitID = UnitID.UnitID";
           SqlDataAdapter da = new SqlDataAdapter(cmd);
           DataSet ds = new System.Data.DataSet();
           da.Fill(ds, "Materials");
           cmbMaterialID.DataSource = ds.Tables["Materials"];
           cmbMaterialID.DisplayMember = "MaterialName";
           cmbMaterialID.ValueMember = "MaterialID";
           con.Close();
       }

       private void btnAdd_Click(object sender, EventArgs e)
       {
           con.Open();
           SqlCommand cmd = new SqlCommand();
           cmd.Connection = con;
           cmd.CommandText = "INSERT INTO SupplierMaterials VALUES (@SupplierID, @MaterialID);";
           cmd.Parameters.AddWithValue("@SupplierID", cmbSupplierID.SelectedValue);
           cmd.Parameters.AddWithValue("@MaterialID", cmbMaterialID.SelectedValue);
           cmd.ExecuteNonQuery();
           con.Close();
       }

       private void Add_Load(object sender, EventArgs e)
       {
           GetMaterials();
           GetSuppliers();

       }

    }
}

Answer 1

SqlConnection class 实施 IDisposable。所以你直接使用 Dispose() 方法。有效的方法是使用 using 块

要保证连接一直关闭，打开里面的连接 using block，如以下代码片段所示。这样做可以确保代码退出块时连接自动关闭

using(SqlConnection connection = new SqlConnection(Helper.GetCon()))
{
// Do something 
}// Here it will automatically call Dispose()

您仍然需要打开连接，但不需要关闭它，因为正如我提到的，Dispose() 方法将处理 using 块末尾的对象

Answer 2

Using (SqlConnection con = new SqlConnection(Helper.GetCon()))
{
 //Your rest of the code inside here.
}

这会关闭您的连接，但您必须手动打开它。 con.Open();

Answer 3

用下面的条件代替 con.open();

if (con.State == ConnectionState.Closed)
   {
        con.Open();
   }

Answer 4

似乎 GetSuppliers() ` 之一直到您设置的部分才执行

con.Close()

你有两个选择：

1.Open 仅连接一次并在每个方法中使用它而不关闭它并在 Application.Exit:

上关闭它

     public Add()
            {
                InitializeComponent();
                con.Open();
            }
.........
 private void Add_Closing(object sender, EventArgs e)
       {
         con.Close();
       }

在每次尝试打开 con 时设置此检查：

if (con.State == ConnectionState.Closed) { con.Open(); }

Visual Studio 和 SQL 错误连接未关闭。连接的当前状态是打开的

Visual Studio and SQL Error The connection was not closed. The connection's current state is open

c#

visual-studio-2010

sql-server-2008