使用c#在两个组合框之间执行If-else语句

我在编码中实现了两个组合框。第一个组合框包含城市名称，第二个组合框则包含该城市的POI。现在我想在这两个组合框之间实现if-else语句。假设如果我选择第一个组合框，按钮将只为第一个启用，然后如果我选择第二个组合框则按钮将为第二个工作。我不知道怎么做。我的代码就像这个

public void Download_Click(object sender, EventArgs e)
{
   // if combox1 select
   // all function will work for combobox 1
   //else if combobox2 select
   //combobbox1 disabled and all function will work for combobx2    
}

最初，我创建了一个类来设置combobox1的值，就像这个一样

            class PlaceList
                {
                    public static ComboBox Combo_list = new ComboBox();
                    public static DataGridView dataTable = new DataGridView();
                    public static void List()
                    {
                        var startPath = Application.StartupPath;
                        string folderName = Path.Combine(startPath, "POI_List");
                        System.IO.Directory.CreateDirectory(folderName);
                        string SavedfileName = "POI_list.json";
                        var Saving_path = Path.Combine(folderName, SavedfileName);
                        string fileName = "Zensus_Gemeinden_org.xlsx";
                        var path = Path.Combine(startPath, fileName);
                        String name = "Gemeinden_31.12.2011_Vergleich";
                        String constr = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" +
                                       path + ";Extended Properties='Excel 12.0 XML;HDR=YES;';";
                        OleDbConnection con = new OleDbConnection(constr);
                        OleDbCommand oconn = new OleDbCommand("Select [3] as City,[4] as Population, * From [" + name + "$D7:E11300] Where [4] > 10000", con);
                        con.Open();
                        OleDbDataAdapter sda = new OleDbDataAdapter(oconn);
                        DataTable data = new DataTable();
                        sda.Fill(data);
                        dataTable.DataSource = data;

                        for (int i = 0; i < data.Rows.Count; i++)
                        {
                            Combo_list.Items.Add(data.Rows[i]["City"]);
                        }

                        string Place_Json = "Place_List:" + JsonConvert.SerializeObject(data, Formatting.Indented);
                        File.WriteAllText(Saving_path, Place_Json);
                    }
                }
   }

然后在Form1.cs中，我创建了

   Dictionary<string, List<string>> poi = new Dictionary<string, List<string>>();

    private void LoadKeys()
    {
       foreach (string line in File.ReadLines("TextFile1.txt"))
                {
                    string[] parts = line.Split(new char[] { ';' }, StringSplitOptions.RemoveEmptyEntries);
                    poi.Add(parts[0], new List<string>());
                    poi[parts[0]] = new List<string>(parts.Skip(1));
                }
    }
    void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (comboBox1.SelectedItem != null)
        {
            string txt = comboBox1.SelectedItem.ToString();
            if (poi.ContainsKey(txt))
            {
                List<string> points = poi[txt];
                comboBox2.Items.Clear();
                comboBox2.Items.AddRange(points.ToArray());
            }
        }
    }

这意味着combobox2依赖于combobox1。它将根据combobox1 给出地名

然后最后在form1.cs按钮1中，我试图做一些类似的事情

    public Form1()
    {
        InitializeComponent();

        PlaceList.Combo_list = comboBox1;
        PlaceList.List();
        LoadKeys();

    }

    private void button1_Click(object sender, EventArgs e)
    {
        if (comboBox1.SelectedIndex != 0)
        {
            ShortText.txt1 = richTextBox1;
            ShortText.shortText(comboBox1.Text);
        }
        else if (comboBox2.SelectedIndex != 0)
        {
            ShortText.txt1 = richTextBox1;
            ShortText.shortText(comboBox2.Text);
        }
        else
        {
            MessageBox.Show("Error");
        }

if(combo1.SelectedIndex != 0){
    //do something
}
else if(combo2.SelectedIndex != 0) {
    //do something else
}
else {
    // Error: You need to select something!
}