vb.net我一直在测试sqlconnection错误

Question

  Private Sub MetroButton1_Click(sender As Object, e As EventArgs) Handles MetroButton1.Click
    If MetroTextBox1.Text <> "" And MetroTextBox2.Text <> "" And MetroComboBox1.SelectedItem <> "" And MetroComboBox2.SelectedItem <> "" Then
        conn.Open()
        Label6.Text = Val(NumericUpDown1.Value)
        Dim cmd As New SqlCommand("select * from books where bname=@book and bpub=@pub and byear=@year and btype=@type", conn)
        cmd.Parameters.AddWithValue("@book", MetroTextBox1.Text)
        cmd.Parameters.AddWithValue("@pub", MetroTextBox2.Text)
        cmd.Parameters.AddWithValue("@year", Label6.Text)
        cmd.Parameters.AddWithValue("@type", MetroComboBox1.Text)
        read = cmd.ExecuteReader
        If read.HasRows Then
            MsgBox("Add New Books or anothe published copy of it!", MsgBoxStyle.Exclamation, "The Same Book Already Exist!")
        Else
            read.Close()
            comm.CommandText = "insert into [books] values('" + MetroTextBox1.Text + "','" + MetroTextBox2.Text + "','" + Label6.Text + "','" + MetroComboBox1.SelectedItem + "','" + MetroComboBox2.SelectedItem + "') "
            comm.ExecuteNonQuery()
            conn.Close()
        End If
    ElseIf MetroTextBox1.Text = "" And MetroTextBox2.Text = "" And MetroComboBox1.SelectedItem = "" And MetroComboBox2.SelectedItem = "" Then
        sound.Play()
        MetroTile1.Text = "Requierd value is missing"
        MetroTile1.ForeColor = Color.Red
        ErrorProvider1.SetError(MetroTextBox1, "Requierd value is missing")
        ErrorProvider2.SetError(MetroTextBox2, "Requierd value is missing")
        ErrorProvider3.SetError(MetroComboBox1, "Requierd value is missing")
        ErrorProvider4.SetError(MetroComboBox2, "Requierd value is missing")
    ElseIf MetroTextBox1.Text <> "" And MetroTextBox2.Text = "" And MetroComboBox1.SelectedItem = "" And MetroComboBox2.SelectedItem = "" Then
        sound.Play()
        MetroTile1.Text = "Requierd value is missing"
        MetroTile1.ForeColor = Color.Red
        ErrorProvider2.SetError(MetroTextBox2, "Requierd value is missing")
        ErrorProvider3.SetError(MetroComboBox1, "Requierd value is missing")
        ErrorProvider4.SetError(MetroComboBox2, "Requierd value is missing")
    ElseIf MetroTextBox1.Text <> "" And MetroTextBox2.Text <> "" And MetroComboBox1.SelectedItem = "" And MetroComboBox2.SelectedItem = "" Then
        sound.Play()
        MetroTile1.Text = "Requierd value is missing"
        MetroTile1.ForeColor = Color.Red
        ErrorProvider3.SetError(MetroComboBox1, "Requierd value is missing")
        ErrorProvider4.SetError(MetroComboBox2, "Requierd value is missing")
    ElseIf MetroTextBox1.Text <> "" And MetroTextBox2.Text <> "" And MetroComboBox1.SelectedItem <> "" And MetroComboBox2.SelectedItem = "" Then
        sound.Play()
        MetroTile1.Text = "Requierd value is missing"
        MetroTile1.ForeColor = Color.Red
        ErrorProvider4.SetError(MetroComboBox2, "Requierd value is missing")
    ElseIf MetroTextBox1.Text = "" And MetroTextBox2.Text <> "" And MetroComboBox1.SelectedItem = "" And MetroComboBox2.SelectedItem = "" Then
        sound.Play()
        ErrorProvider1.SetError(MetroTextBox1, "Requierd value is missing")
        ErrorProvider3.SetError(MetroComboBox1, "Requierd value is missing")
        ErrorProvider4.SetError(MetroComboBox2, "Requierd value is missing")
    ElseIf MetroTextBox1.Text = "" And MetroTextBox2.Text = "" And MetroComboBox1.SelectedItem <> "" And MetroComboBox2.SelectedItem = "" Then
        sound.Play()
        MetroTile1.Text = "Requierd value is missing"
        MetroTile1.ForeColor = Color.Red
        ErrorProvider1.SetError(MetroTextBox1, "Requierd value is missing")
        ErrorProvider2.SetError(MetroTextBox2, "Requierd value is missing")
        ErrorProvider4.SetError(MetroComboBox2, "Requierd value is missing")
    ElseIf MetroTextBox1.Text = "" And MetroTextBox2.Text = "" And MetroComboBox1.SelectedItem = "" And MetroComboBox2.SelectedItem <> "" Then
        sound.Play()
        MetroTile1.Text = "Requierd value is missing"
        MetroTile1.ForeColor = Color.Red
        ErrorProvider1.SetError(MetroTextBox1, "Requierd value is missing")
        ErrorProvider2.SetError(MetroTextBox2, "Requierd value is missing")
        ErrorProvider3.SetError(MetroComboBox1, "Requierd value is missing")
    Else
        sound.Play()
        ErrorProvider1.SetError(MetroTile1, "Requierd value is missing")
        MetroTile1.Text = "Requierd value is missing"
        MetroTile1.ForeColor = Color.Red
    End If
    conn.Close()
    loadlb()
End Sub

我是vb.net的新手我在执行阅读器时总是在SqlConnection中收到错误我总是将连接传递给它，但我一直说连接需要首先打开我无法理解它是怎么回事工作我通常使用mysql，所以如果你们中的任何人都可以告诉我发生了什么，我会很感激。

我的第二个问题是用户输入的验证我需要快速检查每个字段中的用户输入而不写出所有这些代码行