创建新的 SqlDataAdapter 时出现 C# InvalidOperationException

我编写了一些代码来建立与 SQL Server 的连接，然后执行 select 过程以从 SQL Server 中的数据表中获取所有数据，但它在声明新的 SqlDataAdapter 的命令中抛出 InvalidOperationException，请帮助我解决此问题错误。

public class dBConnect
{
    //create SQLconnection variable
    private SqlConnection con;
    //create default constructor that passing a string to con
    public dBConnect()
    {
        try
        {
            con = new SqlConnection(@"Server=Trump\SQLEXPRESS;
        Database=Demo;User Id=sa;Password = stevejobs;");
        }
        catch(Exception exCon)
        {
            Console.WriteLine("Unable to connect to database: {0}", exCon);
        }
    }
    //create Select method to Pour the data into the DataTable
    public DataTable SelectAll(string procName, SqlParameter[] para = null)
    {
        //create a DataTable to store Data from DB
        DataTable dt = new DataTable();
        //create SQLCommand
        SqlCommand cmd = new SqlCommand(procName, con);
        //declare that cmdType is sp
        cmd.CommandType = CommandType.StoredProcedure;
        //input parameter of cmd
        if (para != null)
            cmd.Parameters.AddRange(para);
        //create dataAdapter object

        //InvalidOperationException was thrown at here
        SqlDataAdapter da = new SqlDataAdapter(cmd);

        //declare that cmd is select command of da 
        da.SelectCommand = cmd;
        //use try/catch/finally to establish a connection
        try
        {
            con.Open();
            da.Fill(dt);
        }
        catch(Exception sqlEx)
        {
            Console.WriteLine(@"：Unable to establish a connection: {0}", sqlEx);
        }
        finally
        {
            con.Close();
            con.Dispose();
        }
        return dt;
    }
}

}

你应该：

cmd.CommandText = "your Stored Procedure here.";
cmd.CommandType = CommandType.StoredProcedure;
//input parameter of cmd
if (para != null)
cmd.Parameters.AddRange(para);
//create dataAdapter object

把你的con.Open(); above

or

看看这个步骤

 DataTable dt = new DataTable();
 using (SqlConnection con = new SqlConnection(connectionString))
 {
     con.Open();
      using (SqlCommand cmd = con.CreateCommand())
      {
       //sample stored procedure with parameter:
       // "exec yourstoredProcedureName '" + param1+ "','" + param2+ "'";
       cmd.CommandText = "Your Stored Procedure Here";
       cmd.CommandType =CommandType.StoredProcedure;
       using (SqlDataAdapter adp = new SqlDataAdapter(cmd))
        {
            adp.Fill(dt);
             return dt;
        }
      }
  }