Dim myconn As New SqlClient.SqlConnection("initial catalog = universities;data source=.;integrated security = SSPI;")
Dim mysql As String = "select ynum, yname,ypass,ymail from customer where yname='" & Me.TextBox1.Text.Trim & "'"
Dim adapter As New SqlDataAdapter(mysql, myconn)
Dim mydataset As New DataSet
mydataset.Clear()
adapter.Fill(mydataset, "用户名")
DataGridView1.DataSource = mydataset.Tables("用户名")
If mydataset.Tables("用户名").Rows.Count = 0 Then
MsgBox("用户名不存在，请先注册")
TextBox1.Text = ""
TextBox2.Text = ""
Exit Sub
Else
If TextBox2.Text = DataGridView1.CurrentRow.Cells(2).Value.ToString Then
Form2.ShowDialog()
Else
MsgBox("密码错误请重新输入")
TextBox2.Text = ""
Exit Sub
End If
这是我的详细代码，求高手指教如何修改？

先判断
DataGridView1.CurrentRow.Cells(2) 是不是空对象，防止对空对象的非法访问