Code:
Imports System
Imports System.Collections.Generic
Imports System.ComponentModel
Imports System.Drawing
Imports System.Text
Imports System.Windows.Forms
Imports Microsoft.VisualBasic
Public Class hesap
#Region " text alan "
    Protected Overrides Sub OnResize(ByVal e As EventArgs)
        MyBase.OnResize(e)
        Me.Button1.Left = (Me.MaskedTextBox1.Width - Me.Button1.Width)
    End Sub
#End Region
#Region " Plan Tanıtım "
    Protected Class hesapplani
        Inherits System.Windows.Forms.Form
        Private Mydgv As hesap
        Private WithEvents dgv As System.Windows.Forms.DataGridView

        Public Sub New(ByRef plan As hesap)
            Mydgv = plan

            Me.dgv = New System.Windows.Forms.DataGridView
            Me.SuspendLayout()

            Me.dgv.Location = New System.Drawing.Point(0, 0)
            Me.dgv.Margin = New System.Windows.Forms.Padding(0)
            Me.dgv.Name = "datagrid"
            Me.dgv.TabIndex = 0
            Me.dgv.Dock = DockStyle.Fill


            Me.AutoScaleDimensions = New System.Drawing.SizeF(6.0!, 13.0!)
            Me.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font
            Me.ClientSize = New System.Drawing.Size(295, 614)
            Me.ControlBox = True
            Me.Controls.Add(Me.dgv)
            Me.FormBorderStyle = System.Windows.Forms.FormBorderStyle.Sizable
            Me.MaximizeBox = True
            Me.MinimizeBox = True
            Me.Name = "Hesap Planı"
            'Me.ShowIcon = False
            Me.ShowInTaskbar = False
            Me.StartPosition = System.Windows.Forms.FormStartPosition.CenterScreen
            Me.ResumeLayout(False)


        End Sub

        Private Sub hesapplani_Load(sender As Object, e As EventArgs) Handles Me.Load
            If baglanti.State = ConnectionState.Closed Then baglanti.Open()
            dategetir(dgv, "select kodu,adi from hesapplani")
            baglanti.Close()

        End Sub
    End Class
#End Region

    Private Sub MaskedTextBox1_GotFocus(sender As Object, e As EventArgs) Handles MaskedTextBox1.GotFocus
        MaskedTextBox1.Select(0, 1)
    End Sub
    Private Sub MaskedTextBox1_Resize(ByVal sender As Object, ByVal e As System.EventArgs) _
    Handles MaskedTextBox1.Resize
        ' SetButton()
        Me.Height = MaskedTextBox1.Height
    End Sub

    Private Sub MaskedTextBox1_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) _
    Handles MaskedTextBox1.TextChanged
        'RaiseEvent TextChanged(Me, EventArgs.Empty)
    End Sub
    Private hesaplar As hesapplani

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        If hesaplar Is Nothing Then hesaplar = New hesapplani(Me)
        hesaplar.ShowDialog()
    End Sub
    Private Sub dgv_CellMouseClick(sender As Object, e As DataGridViewCellMouseEventArgs)
        Me.MaskedTextBox1.Text = Me.dgv.Rows(Me.dgv.CurrentRow.Index).Cells(0).Value
    End Sub
End Class
ERROR

Code:
 Private Sub dgv_CellMouseClick(sender As Object, e As DataGridViewCellMouseEventArgs)
        Me.MaskedTextBox1.Text = Me.dgv.Rows(Me.dgv.CurrentRow.Index).Cells(0).Value
    End Sub
I can not select data from datagrid