使用vb.net保留我在数据网格视图的框中选中的值

Private selectedValue As String

Private Sub DataGridView1_SelectionChanged(sender As Object, e As EventArgs) Handles DataGridView1.SelectionChanged
    If DataGridView1.SelectedRows.Count > 0 Then
        selectedValue = DataGridView1.SelectedRows(0).Cells("ColumnName").Value.ToString()
    End If
End Sub

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    If Not String.IsNullOrEmpty(selectedValue) Then
        MessageBox.Show("选中的值是：" & selectedValue)
    Else
        MessageBox.Show("没有选中任何值。")
    End If
End Sub