为什么MessageBox显示NULL值？ [英] Why does the MessageBox show NULL values?

问题描述

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

namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }



        private void button1_Click(object sender, EventArgs e)
        {
            string connetionString = null; 
            SqlConnection connection ; 
            SqlDataAdapter adapter ; 
            DataSet ds = new DataSet(); 
            int i = 0;
            connetionString = NULL;
            connection = new SqlConnection(connetionString); 
            try { 
                connection.Open();
                adapter = new SqlDataAdapter("select *from New", connection); 
                adapter.Fill(ds); 
                connection.Close(); 
                for (i = 0; i <= ds.Tables[0].Rows.Count - 1; i++) { 
                    MessageBox.Show (ds.Tables[0].Rows[i].ItemArray[0].ToString()); 
                } 
            } 
            catch (Exception ex) { 
                MessageBox.Show(ex.ToString()); 
            } 
        }
    }
}

推荐答案

connetionString = NULL;
connection = new SqlConnection(connetionString);

首先，这甚至不会编译为C＃是区分大小写的并且 null 关键字是小写的。

第二，在这两行中是不是有什么东西会扰乱你？

第三，为什么只是启动调试会话并看看发生了什么？

First, this would not even compile as C# is case sensitive and null keyword is lower case.
Second, isn't there something that disturbs you in these two lines?
Third, why nost just starting a debug session and see what is going on?

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