System.InvalidCastException：'指定的强制转换无效。'

问题描述

您好我在2017年Visual Studio社区中创建了一个IT库应用程序，代码在asp.net / C＃中。当我将数据提交到SQL表时，我收到此错误 

Hi i am creating a IT Inventory application in visual studio community 2017 , the code is in asp.net / C#. When i submit the data to the SQL table i received this error 

System.InvalidCastException：'指定的强制转换无效。'

我的sql表查询是：

CREATE TABLE [dbo]。[工作站]（

[Emp_Id] [int] IDENTITY（1,1）NOT NULL，

[Emp_Name] [varchar]（30）NOT NULL，

[Emp_Surname] [varchar]（30）NOT NULL，

[部门] [varchar]（50）NOT NULL，

[Company] [varchar]（30）NOT NULL，

[Hostname] [ nvarchar]（20）NOT NULL，

[Wkst_Status] [varchar]（15）NOT NULL，

[Make] [varchar]（12）NOT NULL，

[型号] [varchar]（15）NOT NUL L，

[SerialNumber] [nvarchar]（30）NOT NULL，

[ProductNumber] [nvarchar]（30）NOT NULL，

[Purch_Date ] [date] NOT NULL，

[WExpiry_Date] [date] NOT NULL，

[Memory] ​​[nvarchar]（6）NOT NULL，

[Processor] [nvarchar]（10）NOT NULL，

[HDD] [nvarchar]（10）NOT NULL，

[OS] [nvarchar]（25）NOT NULL，

  CONSTRAINT [PK__Workstat__262359ABF6F5A9AA] PRIMARY KEY CLUSTERED 

（

[Emp_Id] ASC

）WITH（ PAD_INDEX = OFF，STATISTICS_NORECOMPUTE = OFF，IGNORE_DUP_KEY = OFF，ALLOW_ROW_LOCKS = ON，ALLOW_PAGE_LOCKS = ON）ON [PRIMARY]

）ON [PRIMARY]

GO

CREATE TABLE [dbo].[Workstations](
[Emp_Id] [int] IDENTITY(1,1) NOT NULL,
[Emp_Name] [varchar](30) NOT NULL,
[Emp_Surname] [varchar](30) NOT NULL,
[Department] [varchar](50) NOT NULL,
[Company] [varchar](30) NOT NULL,
[Hostname] [nvarchar](20) NOT NULL,
[Wkst_Status] [varchar](15) NOT NULL,
[Make] [varchar](12) NOT NULL,
[Model] [varchar](15) NOT NULL,
[SerialNumber] [nvarchar](30) NOT NULL,
[ProductNumber] [nvarchar](30) NOT NULL,
[Purch_Date] [date] NOT NULL,
[WExpiry_Date] [date] NOT NULL,
[Memory] [nvarchar](6) NOT NULL,
[Processor] [nvarchar](10) NOT NULL,
[HDD] [nvarchar](10) NOT NULL,
[OS] [nvarchar](25) NOT NULL,
 CONSTRAINT [PK__Workstat__262359ABF6F5A9AA] PRIMARY KEY CLUSTERED 
(
[Emp_Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO

我的C＃代码 ，错误出现在   if（（bool）item [" Wkst_Status"]）

使用System;

使用System.Collections.Generic;

使用System.ComponentModel;

使用System.Data ;

使用System.Data.SqlClient;

使用System.Drawing;

使用System.Linq;

使用System.Text;
$
使用System.Threading.Tasks;

使用System.Windows.Forms;

使用System.Configuration;



$
$ b命名空间库存数据库$
{

  ;  公共部分班级工作站：表格

    {

  &NBSP; &NBSP; &NBSP;私有IEnumerable< object>查询;



  &NBSP; &NBSP; &NBSP;公共对象WExpiry_Date {get;私人集; }


  &NBSP; &NBSP; &NBSP;公共工作站（）

  &NBSP; &NBSP; &NBSP; {

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; InitializeComponent（）;

  &NBSP; &NBSP; &NBSP; }


  &NBSP; &NBSP; &NBSP; private void label1_Click（object sender，EventArgs e）

  &NBSP; &NBSP; &NBSP; {

$
  &NBSP; &NBSP; &NBSP; }


  &NBSP; &NBSP; &NBSP; private void label1_Click_1（object sender，EventArgs e）

  &NBSP; &NBSP; &NBSP; {

$
  &NBSP; &NBSP; &NBSP; }


  &NBSP; &NBSP; &NBSP; private void Workstations_Load（object sender，EventArgs e）

  &NBSP; &NBSP; &NBSP; {

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; // TODO：这行代码将数据加载到'iTInventoryDataSet.Workstations'表中。您可以根据需要移动或移除它。

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; //this.workstationsTableAdapter.Fill(this.iTInventoryDataSet.Workstations）;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; comboBox3.SelectedIndex = 0;

  &NBSP; &NBSP; &NBSP; }


  &NBSP; &NBSP; &NBSP; private void button1_Click（object sender，EventArgs e）

  &NBSP; &NBSP; &NBSP; {

$
  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; SqlConnection con = new SqlConnection（@"Data Source = sh-jasonk \ dev; Initial Catalog = ITInventory; Integrated Security = True"）;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; //插入逻辑

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; con.Open（）;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; bool Wkst_Status = false;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; if（comboBox3.SelectedIndex == 0）

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; {

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; Wkst_Status = true;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; }¥b $ b  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP;否则

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; {

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; Wkst_Status = false;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; }


  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; SqlCommand cmd = new SqlCommand



  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; （@"INSERT INTO [dbo]。[工作站]

      （

     &NBSP;&NBSP; [EMP_NAME]

&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP; [Emp_Surname]

&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP ;，[部门]

      ，[Company]

      ， [主机名]

&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP; [Wkst_Status]

&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;，[使]¥b $ b      ，[Model]

      ，[SerialNumber]
&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP; [ProductNumber]

&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP; [Purch_Date]

&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP; [WExpiry_Date]

&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;，[存储器]

      ，[Processor]

& NBSP; &NBSP; &NBSP; &NBSP; &NBSP;  ，[HDD]

  &NBSP; &NBSP; &NBSP; &NBSP;  ，[OS]）



  &NBSP;   VALUES

  &NBSP; &NBSP; &NBSP; &NBSP;  （'" + txtName.Text +"'，'" + txtSurname.Text +"'，'" + comboBox1.Text +"'，'" + comboBox2.Text +"' ，'" + txtHostName.Text +"'，'"
+ comboBox3.SelectedIndex +"'，'" + txtMake.Text +"'，'" + txtModel.Text +" ;'，'" + txtSN.Text +"'，'" + txtPN.Text +"'，'" + dateTimePicker1.Value.ToString（" yyyy / MM / dd"）
+"'，'" + dateTimePicker1.Value.ToString（" yyyy / MM / dd"）+"'，'" + txtMem.Text +"'，'" + txtProc.Text +" ;'，'" + txtHDD.Text +"'，'" + txtOS.Text +"'）"，con）;
$




  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; //此处转换失败

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; cmd.ExecuteNonQuery（）;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; con.Close（）;



  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; //阅读数据

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; SqlDataAdapter sda = new SqlDataAdapter（@" Select  [Emp_Name]，[Emp_Surname]，[Department]，[Company]，[Hostname]，[Wkst_Status]，[Make]，[Model]

                          &NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP; [的SerialNumber]，[ProductNumber]，[Purch_Date]，[WExpiry_Date]，[存储器]，[处理器]，[HDD]

&NBSP;                                ，[OS] From [dbo]。[Workstations]"，con）;



  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; DataTable dt = new DataTable（）;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; sda.Fill（dt）;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; dataGridView1.Rows.Clear（）;



  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; foreach（dt.Rows中的DataRow项目）

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; {

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; int n = dataGridView1.Rows.Add（）;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; dataGridView1.Rows [n] .Cells [0] .Value = item [" Emp_Name"]。ToString（）;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; dataGridView1.Rows [n] .Cells [1] .Value = item [" Emp_Surname"]。ToString（）;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; dataGridView1.Rows [n] .Cells [2] .Value = item [" Department"]。ToString（）;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; dataGridView1.Rows [n] .Cells [3] .Value = item [" Company"]。ToString（）;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; dataGridView1.Rows [n] .Cells [4] .Value = item [" Hostname"]。ToString（）;



  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; if（（bool）item [" Wkst_Status"]）



  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; {

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; dataGridView1.Rows [n] .Cells [5] .Value =" Active"; $
  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; }¥b $ b  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP;否则

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; {

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; dataGridView1.Rows [n] .Cells [5] .Value =" Inactive";

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; }


  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; dataGridView1.Rows [n] .Cells [6] .Value = item [" Make"]。ToString（）;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; dataGridView1.Rows [n] .Cells [7] .Value = item [" Model"]。ToString（）;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; dataGridView1.Rows [n] .Cells [8] .Value = item [" SerialNumber"]。ToString（）;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; dataGridView1.Rows [n] .Cells [9] .Value = item [" ProductNumber"]。ToString（）;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; dataGridView1.Rows [n] .Cells [10] .Value = item [" Purch_Date"]。ToString（）;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; dataGridView1.Rows [n] .Cells [11] .Value = item [" WExpiry_Date"]。ToString（）;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; dataGridView1.Rows [n] .Cells [12] .Value = item [" Memory"]。ToString（）;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; dataGridView1.Rows [n] .Cells [13] .Value = item [" Processor"]。ToString（）;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; dataGridView1.Rows [n] .Cells [14] .Value = item [" HDD"]。ToString（）;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; dataGridView1.Rows [n] .Cells [15] .Value = item [" OS"]。ToString（）;

  &NBSP; &NBSP; &NBSP; &NBSP; &NBSP; }


  &NBSP; &NBSP; &NBSP; }


  &NBSP; &NBSP; &NBSP; private void label17_Click（object sender，EventArgs e）

  &NBSP; &NBSP; &NBSP; {

$
  &NBSP; &NBSP; &NBSP; }¥b $ b  &NBSP; }
}

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



namespace InventoryStock
{
    public partial class Workstations : Form
    {
        private IEnumerable<object> query;

        public object WExpiry_Date { get; private set; }

        public Workstations()
        {
            InitializeComponent();
        }

        private void label1_Click(object sender, EventArgs e)
        {

        }

        private void label1_Click_1(object sender, EventArgs e)
        {

        }

        private void Workstations_Load(object sender, EventArgs e)
        {
            // TODO: This line of code loads data into the 'iTInventoryDataSet.Workstations' table. You can move, or remove it, as needed.
            //this.workstationsTableAdapter.Fill(this.iTInventoryDataSet.Workstations);
            comboBox3.SelectedIndex = 0;
        }

        private void button1_Click(object sender, EventArgs e)
        {

            SqlConnection con = new SqlConnection(@"Data Source=sh-jasonk\dev;Initial Catalog=ITInventory;Integrated Security=True");
            //Insert Logic
            con.Open();
            bool Wkst_Status = false;
            if (comboBox3.SelectedIndex == 0)
            {
                Wkst_Status = true;
            }
            else
            {
                Wkst_Status = false;
            }

            SqlCommand cmd = new SqlCommand

            (@"INSERT INTO [dbo].[Workstations]
           (
           [Emp_Name]
           ,[Emp_Surname]
           ,[Department]
           ,[Company]
           ,[Hostname]
           ,[Wkst_Status]
           ,[Make]
           ,[Model]
           ,[SerialNumber]
           ,[ProductNumber]
           ,[Purch_Date]
           ,[WExpiry_Date]
           ,[Memory]
           ,[Processor]
           ,[HDD]
           ,[OS])

     VALUES
           ('" + txtName.Text + "','" + txtSurname.Text + "','" + comboBox1.Text + "','" + comboBox2.Text + "','" + txtHostName.Text + "','" + comboBox3.SelectedIndex + "','" + txtMake.Text + "','" + txtModel.Text + "','" + txtSN.Text + "','" + txtPN.Text + "','" + dateTimePicker1.Value.ToString("yyyy/MM/dd") + "','" + dateTimePicker1.Value.ToString("yyyy/MM/dd") + "','" + txtMem.Text + "','" + txtProc.Text + "','" + txtHDD.Text + "','" + txtOS.Text + "')",con);


            //Conversion failed here
            cmd.ExecuteNonQuery();
            con.Close();

            //Reading Data
            SqlDataAdapter sda = new SqlDataAdapter(@"Select  [Emp_Name],[Emp_Surname],[Department],[Company],[Hostname],[Wkst_Status],[Make],[Model]
                                                             ,[SerialNumber],[ProductNumber],[Purch_Date],[WExpiry_Date],[Memory],[Processor],[HDD]
                                                             ,[OS] From [dbo].[Workstations]", con);

            DataTable dt = new DataTable();
            sda.Fill(dt);
            dataGridView1.Rows.Clear();

            foreach (DataRow item in dt.Rows)
            {
                int n = dataGridView1.Rows.Add();
                dataGridView1.Rows[n].Cells[0].Value = item["Emp_Name"].ToString();
                dataGridView1.Rows[n].Cells[1].Value = item["Emp_Surname"].ToString();
                dataGridView1.Rows[n].Cells[2].Value = item["Department"].ToString();
                dataGridView1.Rows[n].Cells[3].Value = item["Company"].ToString();
                dataGridView1.Rows[n].Cells[4].Value = item["Hostname"].ToString();

                if ((bool)item["Wkst_Status"])

                {
                    dataGridView1.Rows[n].Cells[5].Value = "Active";
                }
                else
                {
                    dataGridView1.Rows[n].Cells[5].Value = "Inactive";
                }

                dataGridView1.Rows[n].Cells[6].Value = item["Make"].ToString();
                dataGridView1.Rows[n].Cells[7].Value = item["Model"].ToString();
                dataGridView1.Rows[n].Cells[8].Value = item["SerialNumber"].ToString();
                dataGridView1.Rows[n].Cells[9].Value = item["ProductNumber"].ToString();
                dataGridView1.Rows[n].Cells[10].Value = item["Purch_Date"].ToString();
                dataGridView1.Rows[n].Cells[11].Value = item["WExpiry_Date"].ToString();
                dataGridView1.Rows[n].Cells[12].Value = item["Memory"].ToString();
                dataGridView1.Rows[n].Cells[13].Value = item["Processor"].ToString();
                dataGridView1.Rows[n].Cells[14].Value = item["HDD"].ToString();
                dataGridView1.Rows[n].Cells[15].Value = item["OS"].ToString();
            }

        }

        private void label17_Click(object sender, EventArgs e)
        {

        }
    }
}

我做错了什么，我该如何纠正这个问题 

What am i doing wrong and how can i rectify the issue 

推荐答案

在任何一种情况下，我都有一些建议：

1。如果要表示布尔值

1. Store the Wkst_Status as a bit rather than varchar if it is meant to represent a Boolean

2，请将Wkst_Status存储为一个而不是varchar。您对Wkst_Status的值来自组合框的SelectedIndex属性。 我假设组合框中只有两个选项（true / false）和索引0 = false等。 没关系，但你还需要确保选择了一个值，
否则SelectedIndex将等于-1（不能转换为bool）。

2. Your value for Wkst_Status is derived from the SelectedIndex property of a combobox.  I assume the combobox only has two options in it (true/false) and index 0 = false, etc.  That's OK, but you also need to make sure that a value has been selected, otherwise the SelectedIndex will equal -1 (not castable to bool).

3。您可能希望将insert语句移动到字符串变量，以便您可以调试它并验证insert语句是否反映了有效输入

3. you may want to move the insert statement to a string variable so you can debug it and validate the insert statement is reflecting valid input

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