private void button1_Click(object sender, EventArgs e) { SaveFileDialog saveFileDialog1 = new SaveFileDialog(); saveFileDialog1.Filter = "Excel|*.xlsx"; saveFileDialog1.Title = "Save file"; saveFileDialog1.ShowDialog(); // If the file name is not an empty string open it for saving. if (saveFileDialog1.FileName != "" && Path.GetExtension(saveFileDialog1.FileName) == ".xlsx") { _variableService.Export(comboBox1.Text, comboBox2.Text, saveFileDialog1.FileName); } }