无法获取组合框所选值

Question

这是我的代码 -

combo.DisplayMember = "Caption";
combo.ValueMember = "PortName";
combo.Items.Add(new { PortName = "port", Caption = "caption"  });
//Null reference exception here-
String PortName = combo.SelectedValue.ToString();

我想念什么？

更新 -

//the following line has solved my problem-
dynamic item = cmbPortNo.SelectedItem;
string PortName = item.PortName;

Answer 1

也许您只是缺少 combo.SelectedIndex = 0; line

Answer 2

您可能会缺少数据源属性：

List<CaptionPortCollection> list = new List<CaptionPortCollection>();
list.Add(new CaptionPortCollection() { Caption = "HTTP", Port = 80} );
list.Add(new CaptionPortCollection() { Caption = "HTTPS", Port = 443} );
...
combo.DisplayMember = "Caption";
combo.ValueMember = "Port";
combo.DataSource = list;