[0theghost0]

كود :

System.InvalidCastException occurred
 HResult=0x80004002
 Message=Unable to cast object of type 'System.Data.OleDb.OleDbConnection' to type 'System.Data.SqlClient.SqlConnection'.
 Source=autonumber
 StackTrace:
  at autonumber.Form1.Button1_Click(Object sender, EventArgs e) in C:\Users\TheGhost\Documents\Visual Studio 2017\Projects\autonumber\autonumber\Form1.vb:line 7
  at System.Windows.Forms.Control.OnClick(EventArgs e)
  at System.Windows.Forms.Button.OnClick(EventArgs e)
  at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
  at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
  at System.Windows.Forms.Control.WndProc(Message& m)
  at System.Windows.Forms.ButtonBase.WndProc(Message& m)
  at System.Windows.Forms.Button.WndProc(Message& m)
  at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
  at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
  at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
  at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
  at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
  at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
  at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
  at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.OnRun()
  at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.DoApplicationModel()
  at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.Run(String[] commandLine)
  at autonumber.My.MyApplication.Main(String[] Args) in :line 81

وين الخلل

كود :

Imports System.Data.SqlClient

Public Class Form1
   Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
       Dim s As String = "1"
       Dim a As String = "select isnull(max(Cus_ID),0) from Customer"
       Dim comman As New SqlCommand(a, conn)
       conn.Open()

       Dim readr As SqlDataReader = comman.ExecuteReader
       If readr.Read Then
           s = readr.Item(0) + 1
           TextBox1.Text = s

       End If
       conn.Close()
       readr.Close()
   End Sub
End Class