連接未關閉

Question

這是我的頭腦。我嘗試try和catch與finally和其他東西，但此錯誤不斷回來。請有人幫忙。 我的C＃代碼：

void show() 
    { 
     string str = "SELECT PID, Pname, Gender, ContactNum, Category, Department, Ward, AdmitDate, DischargeDate, NumOfDays, CostOfTest, NumOfDocsVisited, DocFee, BedCost, TotalCost, GrandTotal FROM Patient"; 
     cmd = new SqlCommand(str, con); 
      con.Open(); 
      SqlDataAdapter adp = new SqlDataAdapter(cmd); 
      DataTable dt = new DataTable(); 
      adp.Fill(dt); 
      GridView1.DataBind(); 
       con.Close(); 
    } 

錯誤是：

The connection was not closed. The connection's current state is open. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.InvalidOperationException: The connection was not closed. The connection's current state is open.

源錯誤：

Line 50:   string str = "SELECT PID, Pname, Gender, ContactNum, Category, Department, Ward, AdmitDate, DischargeDate, NumOfDays, CostOfTest, NumOfDocsVisited, DocFee, BedCost, TotalCost, GrandTotal FROM Patient"; 
Line 51:    cmd = new SqlCommand(str, con); 
Line 52:     con.Open(); 
Line 53:     SqlDataAdapter adp = new SqlDataAdapter(cmd); 
Line 54:     DataTable dt = new DataTable(); 

堆棧跟蹤：

[InvalidOperationException: The connection was not closed. The connection's current state is open.] 
System.Data.ProviderBase.DbConnectionInternal.TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, DbConnectionOptions userOptions) +14 
System.Data.SqlClient.SqlConnection.TryOpenInner(TaskCompletionSource`1 retry) +94 
System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry) +110 
System.Data.SqlClient.SqlConnection.Open() +96 
SMC.Billing.show() in e:\VS2013 projects\SMC\SMC\Billing.aspx.cs:52 
SMC.Billing.Button3_Click(Object sender, EventArgs e) in e:\VS2013 projects\SMC\SMC\Billing.aspx.cs:97 
System.Web.UI.WebControls.Button.OnClick(EventArgs e) +9628722 
System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +103 
System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10 
System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13 
System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +35 
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1724 

Answer 1

裹在using塊的連接。這保證它總是被關閉。

using (var connection = new SqlConnection(connectionString)) 
{ 
    connection.Open(); 
    //Do stuff with the connection 
} 

Answer 2

在我看來，它試圖告訴你，你正試圖打開一個已經打開的連接。

你可以嘗試（在第52行）

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