未将对象引用设置到对象的实例

[xinguo028]

出错地方:
string dataTableName = "material_import_total";//错误地方
mySqlDataAdapter.Fill(myDataSet,dataTableName);
comboBox1.DataSource = myDataSet.Tables[dataTableName];
comboBox1.DisplayMember = "Supply_company";

全部代码如下:
using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.Data.SqlClient;

namespace Test
{
/// <summary>
/// Form1 的摘要说明。
/// </summary>
public class Form1 : System.Windows.Forms.Form
{
private System.Windows.Forms.ComboBox comboBox1;
/// <summary>
/// 必需的设计器变量。
/// </summary>
private System.ComponentModel.Container components = null;

public Form1()
{
//
// Windows 窗体设计器支持所必需的
//
InitializeComponent();

//
// TODO: 在 InitializeComponent 调用后添加任何构造函数代码
//
}

/// <summary>
/// 清理所有正在使用的资源。
/// </summary>
protected override void Dispose( bool disposing )
{
if( disposing )
{
if (components != null)
{
components.Dispose();
}
}
base.Dispose( disposing );
}

#region Windows 窗体设计器生成的代码
/// <summary>
/// 设计器支持所需的方法 - 不要使用代码编辑器修改
/// 此方法的内容。
/// </summary>
private void InitializeComponent()
{
this.comboBox1 = new System.Windows.Forms.ComboBox();
this.SuspendLayout();
//
// comboBox1
//
this.comboBox1.Location = new System.Drawing.Point(104, 80);
this.comboBox1.Name = "comboBox1";
this.comboBox1.Size = new System.Drawing.Size(121, 20);
this.comboBox1.TabIndex = 0;
//
// Form1
//
this.AutoScaleBaseSize = new System.Drawing.Size(6, 14);
this.ClientSize = new System.Drawing.Size(292, 266);
this.Controls.Add(this.comboBox1);
this.Name = "Form1";
this.Text = "Form1";
this.Load += new System.EventHandler(this.Form1_Load);
this.ResumeLayout(false);

}
#endregion

/// <summary>
/// 应用程序的主入口点。
/// </summary>
[STAThread]
static void Main()
{
Application.Run(new Form1());
}

private void Form1_Load(object sender, System.EventArgs e)
{
string connectionString = "server = hujianfang;" +"database = hbqjcfdb;"+"user = sa;"+"password = sa";
SqlConnection mySqlConnection = new SqlConnection(connectionString);
try
{
string SelectString ="SELECT DISTICT Supply_company FROM material_import_total";
SqlCommand mySqlCommand = mySqlConnection.CreateCommand();
mySqlCommand.CommandText = SelectString;
SqlDataAdapter mySqlDataAdapter = new SqlDataAdapter();
mySqlDataAdapter.SelectCommand = mySqlCommand;
DataSet myDataSet = new DataSet();
mySqlConnection.Open();
string dataTableName = "material_import_total";//错误地方
mySqlDataAdapter.Fill(myDataSet,dataTableName);
comboBox1.DataSource = myDataSet.Tables[dataTableName];
comboBox1.DisplayMember = "Supply_company";
}
catch(Exception ex)
{
MessageBox.Show(ex.Message.ToString());
mySqlConnection.Close();
}
finally{
mySqlConnection.Close();
}
}
}
}

[lovefootball]

不可能的
给字符串赋值怎么会报这个错误

单步调试
看看哪个对象没有实例化

[ztwz]

mySqlConnection.Open();
应该是这错了吧，你标的哪句怎么会错？
是你的mySqlConnection没实例化才对！

[jiatong1981]

try
{
string SelectString ="SELECT DISTICT Supply_company FROM material_import_total";
//SqlCommand mySqlCommand = mySqlConnection.CreateCommand();
//mySqlCommand.CommandText = SelectString;
SqlDataAdapter mySqlDataAdapter = new SqlDataAdapter(SelectString,mySqlConnection);
//mySqlDataAdapter.SelectCommand = mySqlCommand;
DataSet myDataSet = new DataSet();
//mySqlConnection.Open();
string dataTableName = "material_import_total";//错误地方
mySqlDataAdapter.Fill(myDataSet,dataTableName);
comboBox1.DataSource = myDataSet.Tables[dataTableName];
comboBox1.DisplayMember = "Supply_company";
}