ComboBox的SelectedIndex始终为-1

Question

I have a method creating a ComboBox, and on SelectedIndexChanged I need the text so I could use another method, but the SelectedIndex is always -1, no matter what is chosen. I am new to C# so I really do not understand what the problem could be.

This is the method where the ComboBox is created:

public ComboBox GetSize(string uri) {
   xmlReader = GetXmlReader(uri + "/People");
   ComboBox cb = new ComboBox();
   while (xmlReader.ReadToFollowing("site")) {
       cb.Items.Add(xmlReader.GetAttribute(0));
   }
   return cb;
}

This is where it is added to a TabControl:

cb = esrl.GetSize(uri);
cb.SelectedIndexChanged += new System.EventHandler(cb_SelectedIndexChanged);
page.Controls.Add(cb);

And this is where I try to get the information about the SelectedItem text, but the Index is always -1.

private void cb_SelectedIndexChanged(object sender, EventArgs e) {
    string attribute = cb.Items[cb.SelectedIndex].ToString();
    MessageBox.Show( " " + attribute);
}

Answer 1

It's because "cb" is not recognized as this particular ComboBox. Try to declare

ComboBox cb = new ComboBox();

as a field for the whole class.

Answer 2

Try:

private void cb_SelectedIndexChanged(object sender, EventArgs e) {
    ComboBox c = sender as ComboBox;
    if(c == null) return;

    string attribute = c.Items[c.SelectedIndex].ToString();
    MessageBox.Show( " " + attribute);
}

This will make sure you are accessing the same combo box for which the event got fired.