title: populate combobox depending on another combobox
body: <p>im making a wpf wherein one combobox populates depending on another combobox. however, only one combobox populated. </p>
  
  <p>this is my code below. </p>
  
  <pre><code> public partial class Form4 : Form
      {
          public Form4()
          {
              InitializeComponent();
              this.Load += Form4_Load;
          }
  
          string connstring = ("Server=localhost;Port=5432;User Id=postgres;Password=021393;Database=postgres;");
  
          private void Form4_Load(object sender, EventArgs e)
          {
              string query = "SELECT * FROM data_organsystem";            
              fillCombo(comboBox3, query, "name", "id");
              comboBox3_SelectedIndexChanged(null, null);
          }
  
          private void fillCombo(ComboBox combo, string query, string displayMember, string valueMember)
          {
              NpgsqlConnection conn = new NpgsqlConnection(connstring);
              NpgsqlCommand cmd = new NpgsqlCommand(query, conn);
              NpgsqlDataAdapter da = new NpgsqlDataAdapter(cmd);
              DataTable dt = new DataTable();
              da.Fill(dt);
              combo.DataSource = dt;             
              combo.DisplayMember = displayMember;            
              combo.ValueMember = valueMember;
          }
  
          private void comboBox3_SelectedIndexChanged(object sender, EventArgs e)
          {
              int val;
              Int32.TryParse(comboBox3.SelectedValue.ToString(), out val);
              string query = "SELECT * FROM data_symptom WHERE organ_system_id = " + val;
              fillCombo(comboBox4, query, "name", "id");
          }
      }
  }
  </code></pre>
  
  <p>if you have any idea on how to edit this code, it would be a big help. thanks!</p>