C＃中的Invalidoperationexception错误 | C＃中的Invalidoperationexception错误

本文介绍了C＃中的Invalidoperationexception错误的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

InvalidOperationException error in C#

我的代码：

My code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;

namespace Expense_System
{
    public partial class Transactions : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {

            String strConnString = ConfigurationManager.ConnectionStrings["conString"].ConnectionString;

            SqlConnection con = new SqlConnection(strConnString);

            con.Open();

            SqlCommand cmd = new SqlCommand("select * from Expense_Type");

            DropDownListexpensetype.DataSource = cmd.ExecuteReader();
            DropDownListexpensetype.DataTextField = "Expense_Type";
            DropDownListexpensetype.DataValueField = "Expense_Type";
            DropDownListexpensetype.DataBind();



        }

        protected void BtncreateExpense_Click(object sender, EventArgs e)
        {


        }

    }
}

我的尝试：

谷歌搜索它但没有得到正确的解决方案

What I have tried:

Googled it but not getting proper solution

推荐答案

protected void Page_Load(object sender, EventArgs e){
      if(!IsPostback){
	          BindList();
       }
}


private void BindList(){
     	String strConnString = ConfigurationManager.ConnectionStrings["conString"].ConnectionString;
            using(SqlConnection con = new SqlConnection(strConnString)){
            	using(SqlCommand cmd = new SqlCommand("select * from Expense_Type", con)){
			         con.Open();
            		DropDownListexpensetype.DataSource = cmd.ExecuteReader();
            		DropDownListexpensetype.DataTextField = "Expense_Type";
            		DropDownListexpensetype.DataValueField = "Expense_Type";
            		DropDownListexpensetype.DataBind();
	    	}
	    }
}

注意：我注意到你已经分配了字段 Expense_Type 适用于文本和值。只需确保 DataValueField 包含唯一值，以避免在从列表中选择/预选值时出现意外行为。

Note: I've noticed that you've assigned the field Expense_Type for both Text and Value. Just make sure that the DataValueField contain unique values to avoid unexpected behavior when selecting/pre-selecting values from the list.

SqlCommand cmd = new SqlCommand("select * from Expense_Type", con);

SqlCommand cmd = new SqlCommand("select * from Expense_Type", con);

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