不能獲得下拉框選擇的值

Question

這裏是我的代碼 -

combo.DisplayMember = "Caption"; 
combo.ValueMember = "PortName"; 
combo.Items.Add(new { PortName = "port", Caption = "caption" }); 

//Null reference exception here- 
String PortName = combo.SelectedValue.ToString(); 

我錯過了什麼？

最新情況：

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

Answer 1

也許你只是缺少combo.SelectedIndex = 0;線

Answer 2

您可能忽略DataSource屬性：

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;