如何修复此错误“从字符串转换为双精度无效” [英] How Can I Fix This Error"Conversion From String To Double Is Not Valid"

问题描述

这是我的代码

  Imports  System.Data.SqlClient 
 公共 类 frmChangePassword 
  Dim  rdr  As  SqlDataReader =  Nothing  
 
  Dim  con  As  SqlConnection =  Nothing  
 
  Dim  cmd  As  SqlCommand =  Nothing  
 私有  Sub  Button1_Click（ ByVal  sender 作为系统。对象， ByVal  e  As  System.EventArgs）句柄 Button1.Click 
 尝试 
  Dim  RowsAffected 作为 整数 =  0  
 如果 Len（Trim（UserName.Text））=  0  然后 
 MessageBox.Show（ 请输入用户名， 输入错误，MessageBoxButtons.OK，MessageBoxIcon。错误）
 UserName.Focus（）
 退出  Sub  
 结束 如果 
 如果 Len（Trim（OldPassword.Text））=  0  然后 
 MessageBox.Show （ 请输入旧密码， 输入错误，MessageBoxButtons.OK，MessageBoxIcon。错误）
 OldPassword.Focus（） 
 退出  Sub  
 结束 如果 
 如果 Len（Trim（NewPassword.Text））=  0  然后 
 MessageBox.Show（ 请输入新密码， 输入错误 ，MessageBoxButtons.OK，MessageBoxIcon。错误）
 NewPassword.Focus（）
 退出  Sub  
 结束 如果 
 如果 Len（Trim（ConfirmPassword.Text））=  0  然后 
 MessageBox.Show（ 请确认新密码， 输入错误，MessageBoxButtons.OK，MessageBoxIcon。错误）
 ConfirmPassword.Focus（）
 退出  Sub  
 结束 如果 
 如果 NewPassword.TextLength<  5  然后 
 MessageBox.Show（ 新密码应为Atleast 5个字符， 输入错误，MessageBoxButtons.OK，MessageBoxIcon。错误）
 NewPassword.Text =   
 ConfirmPassword.Text =   
 NewPassword.Focus（）
 退出  Sub  
  ElseIf  NewPassword.Text<> ConfirmPassword.Text 然后 
 MessageBox.Show（ 密码不匹配， 输入错误，MessageBoxButtons.OK，MessageBoxIcon。 错误）
 NewPassword.Text =    
 OldPassword.Text =   
 ConfirmPassword.Text =   
 OldPassword.Focus（）
 退出  Sub  
  ElseIf  OldPassword.Text = NewPassword.Text < span class =code-keyword>然后 
 MessageBox.Show（ 密码相同..重新输入新密码， 输入错误，MessageBoxButtons.OK，MessageBoxIcon。错误）
 NewPassword.Text = < span class =code-string>  
 ConfirmPassword.Text =   
 NewPassword.Focus（）
 退出  Sub  
 结束 如果 
 
  Dim  ck  As   String  = < span class =code-string>  Data Source = .\SqlExpress;综合安全=真; AttachDbFilename = | DataDirectory目录| \ProductManagerDB.mdf; User Instance = true; 
 
 con = 新 SqlConnection（ck）
 
 con.Open （）
 
  Dim  co <​​span class =code-keyword> As  字符串 =  更新用户设置密码='& NewPassword.Text&  'where username ='& UserName.Text&  '和密码='& OldPassword.Text&  < span class =code-string>' 
 '   
 
 cmd = 新 SqlCommand（co）
 
 cmd.Connection = con 
 RowsAffected = cmd.ExecuteNonQuery（ ）
 如果 RowsAffected>  0  然后 
 
 MessageBox.Show（ 已成功更改， 密码，MessageBoxButtons.OK，MessageBoxIcon.Information）
  Me  .Hide（）
 UserName.Text =   
 NewPassword.Text =  < span class =code-string> 
 OldPassword.Text =   
 ConfirmPassword.Text =   
 
 frmLogin。 Show（）
 frmLogin.UserName.Text =   
 frmLogin.Password.Text =   
 
 
 frmLogin。 UserName.Focus（）
  Else  
 
 MessageBox.Show（ 无效的用户名或密码， 输入错误 ，MessageBoxButtons.OK，MessageBoxIcon。错误）
 UserName.Text =   
 NewPassword.Text =   
 OldPassword.Text =   
 ConfirmPassword.Text = < span class =code-string>  
 UserName.Focus（） 
 结束 如果 
 
 
 
 
 
 
 
 
 如果 con.State = ConnectionState.Open 然后 
 
 con.Close（）
 
 结束 如果 
 con.Close（）
 
 
  Catch  ex  As 异常
 MessageBox.Show（ex.Message， 错误 ，MessageBoxButtons.OK，MessageBoxIcon。错误）
 结束 尝试 
 
 结束  Sub  

解决方案

你从未指出过抛出引发错误的代码行。我找不到它，因为这个代码都没有与Double有任何关系。



这很简单。您正在尝试将一些字符串值分配给已声明为Double的变量。你不能这样做。您必须将字符串转换为Double。



您的SQL容易受到SQL注入攻击。如果有人在你的一个文本框中键入正确的内容，他们可能会破坏整个数据库。 Google for SQL Injection可以了解更多信息。

其中一个参数是从字符串隐式转换为double。



另外，您可以查看在查询中使用命令参数。您提出的查询很容易被 SQL Injection [< a href =http://www.codeproject.com/Articles/459324/Understading-SQL-Injection-and-Creating-SQL-Injecttarget =_ blanktitle =New Window> ^ ]

Here is my code

Imports System.Data.SqlClient
Public Class frmChangePassword
    Dim rdr As SqlDataReader = Nothing

    Dim con As SqlConnection = Nothing

    Dim cmd As SqlCommand = Nothing
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Try
            Dim RowsAffected As Integer = 0
            If Len(Trim(UserName.Text)) = 0 Then
                MessageBox.Show("Please enter user name", "Input Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
                UserName.Focus()
                Exit Sub
            End If
            If Len(Trim(OldPassword.Text)) = 0 Then
                MessageBox.Show("Please enter old password", "Input Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
                OldPassword.Focus()
                Exit Sub
            End If
            If Len(Trim(NewPassword.Text)) = 0 Then
                MessageBox.Show("Please enter new password", "Input Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
                NewPassword.Focus()
                Exit Sub
            End If
            If Len(Trim(ConfirmPassword.Text)) = 0 Then
                MessageBox.Show("Please confirm new password", "Input Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
                ConfirmPassword.Focus()
                Exit Sub
            End If
            If NewPassword.TextLength < 5 Then
                MessageBox.Show("The New Password Should be of Atleast 5 Characters", "Input Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
                NewPassword.Text = ""
                ConfirmPassword.Text = ""
                NewPassword.Focus()
                Exit Sub
            ElseIf NewPassword.Text <> ConfirmPassword.Text Then
                MessageBox.Show("Password do not match", "Input error", MessageBoxButtons.OK, MessageBoxIcon.Error)
                NewPassword.Text = ""
                OldPassword.Text = ""
                ConfirmPassword.Text = ""
                OldPassword.Focus()
                Exit Sub
            ElseIf OldPassword.Text = NewPassword.Text Then
                MessageBox.Show("Password is same..Re-enter new password", "Input error", MessageBoxButtons.OK, MessageBoxIcon.Error)
                NewPassword.Text = ""
                ConfirmPassword.Text = ""
                NewPassword.Focus()
                Exit Sub
            End If

            Dim ck As String = "Data Source=.\SqlExpress; Integrated Security=True; AttachDbFilename=|DataDirectory|\ProductManagerDB.mdf; User Instance=true;"

            con = New SqlConnection(ck)

            con.Open()

            Dim co As String = "Update Users set Password = '" & NewPassword.Text & "'where username='" & UserName.Text & "' and Password = '" & OldPassword.Text & "'"
            '

            cmd = New SqlCommand(co)

            cmd.Connection = con
            RowsAffected = cmd.ExecuteNonQuery()
            If RowsAffected > 0 Then

                MessageBox.Show("Successfully changed", "Password", MessageBoxButtons.OK, MessageBoxIcon.Information)
                Me.Hide()
                UserName.Text = ""
                NewPassword.Text = ""
                OldPassword.Text = ""
                ConfirmPassword.Text = ""

                frmLogin.Show()
                frmLogin.UserName.Text = ""
                frmLogin.Password.Text = ""


                frmLogin.UserName.Focus()
            Else

                MessageBox.Show("invalid user name or password", "input error", MessageBoxButtons.OK, MessageBoxIcon.Error)
                UserName.Text = ""
                NewPassword.Text = ""
                OldPassword.Text = ""
                ConfirmPassword.Text = ""
                UserName.Focus()
            End If








            If con.State = ConnectionState.Open Then

                con.Close()

            End If
            con.Close()


        Catch ex As Exception
            MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
        End Try

    End Sub

解决方案

You never pointed out the line of code that throws the error. I can't find it as none of this code should have anything to do with a Double.

It's simple really. You're trying to assign some string value to a variable that has been declared Double. You can't do that. You have to convert the string to a Double.

You SQL is susceptible to SQL Injection attacks. If someone typed the right thing into one of your text boxes they could destroy your entire database. Google for SQL Injection to find out more.

One of the parameters is getting converted from string to double implicitly.

Additionally, you can look at using command parameters in your query. You present query is an easy prey to SQL Injection[^].

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