已经有一个与此命令相关的开放式数据读取器，必须先关闭它。？8

Question

我试图将图像文件以二进制格式保存到数据库中。并检索这些二进制文件，并在我的网页上显示图像。在使用下面的代码时，会产生一个错误。请帮帮我。

public partial class Default3 : System.Web.UI.Page 
{ 
    static SqlConnection con = new SqlConnection(@"connectionString"); 
    protected void Page_Load(object sender, EventArgs e) 
    { 
     if (!IsPostBack) 
     { 
      filldropdown(); 
     } 
    } 

    private void filldropdown() 
    { 
     SqlCommand cmd = new SqlCommand("Select EmpID from Tbl_Emp", con); 
     if (con.State == ConnectionState.Closed) 
     { 
      con.Open(); 
     } 
     SqlDataReader dr = cmd.ExecuteReader(); 
     TextBox3.Items.Clear(); 
     if (dr.HasRows) 
     { 

      while (dr.Read()) 
      { 
       TextBox3.Items.Add(dr["EmpID"].ToString()); 
      } 
     } 
     con.Close(); 
    } 
    protected void Button1_Click(object sender, EventArgs e) 
    { 
     SqlCommand cmd = new SqlCommand("insert into Tbl_Emp values(@id,@name,@image)", con); 
     cmd.Parameters.AddWithValue("@id", TextBox1.Text); 
     cmd.Parameters.AddWithValue("@name", TextBox2.Text); 

     int img = FileUpload1.PostedFile.ContentLength; 

     byte[] msdata = new byte[img]; 

     FileUpload1.PostedFile.InputStream.Read(msdata, 0, img); 

     cmd.Parameters.AddWithValue("@image", msdata); 

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

     con.Close(); 
     filldropdown(); 
     Response.Write("Data Saved ...."); 

    } 
    protected void Button2_Click(object sender, EventArgs e) 
    { 
     SqlCommand cmd = new SqlCommand("select * from Tbl_Emp where EmpID=@id", con); 
     cmd.Parameters.AddWithValue("@id", TextBox3.Text); 
     if (con.State == ConnectionState.Closed) 
     { 
      con.Open(); 
     } 
     SqlDataReader dr = cmd.ExecuteReader(); 
     if (dr.HasRows && dr.Read()) 
     { 
      TextBox1.Text = dr["EmpID"].ToString(); 
      TextBox2.Text = dr["EmpName"].ToString(); 
      Image1.ImageUrl = "Handler.ashx?EmpID=" + TextBox3.Text; 
     } 
     else 
     { 
      Response.Write("Record With This ID Note Found"); 
     } 
    } 
} 

来源：

<div> 
     Enter ID <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox><br /> 
     Enter Name <asp:TextBox ID="TextBox2" runat="server"></asp:TextBox><br /> 
     Enter Pic <asp:FileUpload ID="FileUpload1" runat="server" /><br /> 
     <asp:Button ID="Button1" runat="server" Text="Save" onclick="Button1_Click" /><br > 
     <asp:Image ID="Image1" runat="server" Height="137px" Width="130px" /><br /> 
     <asp:DropDownList ID="TextBox3" runat="server"> 
     </asp:DropDownList> 
     <asp:Button ID="Button2" runat="server" Text="Search" onclick="Button2_Click" /> 

数据表：

Answer 1

这是正确的答案。

public partial class Default3 : System.Web.UI.Page 
{ 
    static SqlConnection con = new SqlConnection(@"connectionString"); 
    protected void Page_Load(object sender, EventArgs e) 
    { 
     if (!IsPostBack) 
     { 
      filldropdown(); 
     } 
    } 

    private void filldropdown() 
    { 
     SqlCommand cmd = new SqlCommand("Select EmpID from Tbl_Emp", con); 
     if (con.State == ConnectionState.Closed) 
     { 
      con.Open(); 
     } 
     SqlDataReader dr = cmd.ExecuteReader(); 
     TextBox3.Items.Clear(); 
     if (dr.HasRows) 
     { 

      while (dr.Read()) 
      { 
       TextBox3.Items.Add(dr["EmpID"].ToString()); 
      } 
     } 
     dr.Close(); 
     con.Close(); 
    } 
    protected void Button1_Click(object sender, EventArgs e) 
    { 
     SqlCommand cmd = new SqlCommand("insert into Tbl_Emp values(@id,@name,@image)", con); 
     cmd.Parameters.AddWithValue("@id", TextBox1.Text); 
     cmd.Parameters.AddWithValue("@name", TextBox2.Text); 

     int img = FileUpload1.PostedFile.ContentLength; 

     byte[] msdata = new byte[img]; 

     FileUpload1.PostedFile.InputStream.Read(msdata, 0, img); 

     cmd.Parameters.AddWithValue("@image", msdata); 

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

     con.Close(); 
     filldropdown(); 
     Response.Write("Data Saved ...."); 

    } 
    protected void Button2_Click(object sender, EventArgs e) 
    { 
     SqlCommand cmd = new SqlCommand("select * from Tbl_Emp where EmpID=@id", con); 
     cmd.Parameters.AddWithValue("@id", TextBox3.Text); 
     if (con.State == ConnectionState.Closed) 
     { 
      con.Open(); 
     } 
     SqlDataReader dr = cmd.ExecuteReader(); 
     if (dr.HasRows && dr.Read()) 
     { 
      TextBox1.Text = dr["EmpID"].ToString(); 
      TextBox2.Text = dr["EmpName"].ToString(); 
      Image1.ImageUrl = "Handler.ashx?EmpID=" + TextBox3.Text; 
     } 
     else 
     { 
      Response.Write("Record With This ID Note Found"); 
     } 
     dr.Close(); 
    } 
} 

Answer 2

你必须开辟新的之一，因为它运行时的对象之前关闭SqlDataReader对象..

这样紧密ID

dr.Close(); 

Answer 3

处理清理SQL连接，命令和读者的最佳方式是使用using声明。此外，您并不需要根据您发布的代码将连接保持为静态字段。这里的基本上是我会在每个方法

protected void Some_Action(object sender, EventArgs e) 
{ 
    using(SqlConnection con = new SqlConnection(@"connectionString")) 
    { 
     con.Open(); 
     using(SqlCommand cmd = new SqlCommand("Query Here", con)) 
     { 
      // Do stuff with the command here like setting Parameters. 
      using(SqlDataReader dr = cmd.ExecuteReader()) 
      { 
       // Do stuff with the reader here 
      } 
     } 
    } 
} 

这样做将确保即使发生异常的连接，命令和Reader配置。

Answer 4

这将是更好地使用Using，它会自动Dispose你的连接/读者什么你已经打开

像

using(SqlConnection con=new SqlConnection) 
    { 
    SqlCommand cmd=new SqlCommand(con,"query") 
    .... 
    using(SqlDataReader dr=cmd.ExecuteReader()) 
     {  .... 
     } 
    } 

但你可以使用像这样在现有的代码

private void filldropdown() 
    { 
     SqlCommand cmd = new SqlCommand("Select EmpID from Tbl_Emp", con); 
     if (con.State == ConnectionState.Closed) 
     { 
      con.Open(); 
     } 
     SqlDataReader dr = cmd.ExecuteReader(); 
     TextBox3.Items.Clear(); 
     if (dr.HasRows) 
     { 

      while (dr.Read()) 
      { 
       TextBox3.Items.Add(dr["EmpID"].ToString()); 
      } 
     } 
     con.Close(); 
    dr.Close 
    } 





protected void Button2_Click(object sender, EventArgs e) 
    { 
     SqlCommand cmd = new SqlCommand("select * from Tbl_Emp where EmpID=@id", con); 
     cmd.Parameters.AddWithValue("@id", TextBox3.Text); 
     if (con.State == ConnectionState.Closed) 
     { 
      con.Open(); 
     } 
     SqlDataReader dr = cmd.ExecuteReader(); 
     if (dr.HasRows && dr.Read()) 
     { 
      TextBox1.Text = dr["EmpID"].ToString(); 
      TextBox2.Text = dr["EmpName"].ToString(); 
      Image1.ImageUrl = "Handler.ashx?EmpID=" + TextBox3.Text; 
     } 
     else 
     { 
      Response.Write("Record With This ID Note Found"); 
     } 
    dr.Close(); 
    }