ExecuteReader：Connection属性尚未初始化为visual studio

Question

我是一个新的学习视觉工作室。我得到一个错误

  

连接属性尚未初始化

这是我的代码：

Imports System.Data.SqlClient

Public Class Form1
Dim con As SqlConnection
Dim cm As SqlCommand
Dim dr As SqlDataReader

Private Sub CheckBox1_CheckedChanged(sender As Object, e As EventArgs) Handles CheckBox1.CheckedChanged
    If CheckBox1.Checked Then
        TextBox2.PasswordChar = ""
    Else
        TextBox2.PasswordChar = "•"
    End If
End Sub

Private Sub Form1_Load(ByVal sender As Object, e As EventArgs) Handles MyBase.Load
    TextBox1.MaxLength = 50
    TextBox2.PasswordChar = "•"
End Sub

Private Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs) Handles Button1.Click
    If TextBox1.Text = "" Or TextBox2.Text = "" Then
        MsgBox("pls fill the data", MsgBoxStyle.Information)
        Exit Sub
    Else
        Call Koneksi()
        cm = New SqlCommand("select*from login where username='" & TextBox1.Text & "'and password" & TextBox2.Text & "'", con)
        cm.Connection = con
        dr = cm.ExecuteReader
        dr.Read()
        last.Show()
        Me.Close()
        If dr.HasRows Then
            MsgBox("succes", MsgBoxStyle.Information, "information")
        Else
            MsgBox("wrong password/username", MsgBoxStyle.Critical)
            TextBox1.Clear()
            TextBox2.Clear()
        End If
    End If

End Sub
End Class