如何解决在 C# 中获取列表框的选定字符串时出现此错误？

Question

I'd like to get a string of a Listbox. This is my code:

db.Employees.Select(x => x.LastName).OrderBy(x => x).ToList().ForEach(x => listBox1.Items.Add(x));
var selectedEmployee = listBox1.SelectedItem.ToString();
Debug.WriteLine(selectedEmployee);

The error I got is System.NullReferenceException . Not sure why though.

So how do I fix this error? By the way, everything is in the Window_Loaded method.

Answer 1

As @ElyasEsna said, you never set listBox1.SelectedItem, and that's why it throws NullReferenceException.

So I rewrote your code this way:

db.Employees.Select(x => x.LastName).OrderBy(x => x).ToList().ForEach(x => listBox1.Items.Add(x));
listBox1.SelectedItem = // list item that you will select, depending on the choice of your program
var selectedEmployee = listBox1.SelectedItem.ToString();
Debug.WriteLine(selectedEmployee);