c# - 格式化字符串的输出

Question

我是 C# 新手。我正在大学的一个模块中学习它。我们接到了一项任务，要求我们使用 Visual Studio 工具箱中包含的各种组件创建一个简单的预订应用程序。

UI 有一个 ListBox，它使用户能够选择将参加事件的多个人的名字。当用户确认选择时，所选项目连接到 String 并在 Label 中输出。

这是我从 ListBox

获取值的代码

 protected void btnRequest_Click(object sender, EventArgs e)
{
    //Update the summary label with the details of the booking.
    n = name.Text;
    en = eventName.Text;
    r = room.SelectedItem.ToString();
    d = cal.SelectedDate.ToShortDateString();

    foreach (ListItem li in attendees.Items)
    {
        if (li.Selected)
        {
            people += li.Text + " ";
        }
    }


    confirmation.Text = r + " has been booked on " + d + " by " + n + " for " + en + ". " + people + " will be attending.";
}

下面是我的全部代码:

public partial class _Default : System.Web.UI.Page
{
    //Variables
    public TextBox name;
    public TextBox eventName;
    public Label confirmation;
    public DropDownList room;
    public Calendar cal;
    public Button btn;
    public ListBox attendees;

    //Booking variables - store all information relating to booking in these variables
    public String n; //name of person placing booking
    public String en; //name of event
    public String r; //room it will take place
    public List<String> att; //list of people attending
    public String d; //date it will be held on

    public String people;

    protected void Page_Load(object sender, EventArgs e)
    {
        //Get references to components
        name = txtName;
        eventName = txtEvent;
        room = droplistRooms;
        attendees = attendeelist;
        cal = Calendar1;
        btn = btnRequest;
        confirmation = lblSummary;

    }
    protected void btnRequest_Click(object sender, EventArgs e)
    {
        //Update the summary label with the details of the booking.
        n = name.Text;
        en = eventName.Text;
        r = room.SelectedItem.ToString();
        d = cal.SelectedDate.ToShortDateString();

        foreach (ListItem li in attendees.Items)
        {
            if (li.Selected)
            {
                people += li.Text + " ";
            }
        }


        confirmation.Text = r + " has been booked on " + d + " by " + n + " for " + en + ". " + people + " will be attending.";
    }

    protected void Calendar1_SelectionChanged(object sender, EventArgs e)
    {
        d = cal.SelectedDate.ToShortDateString();
    }

输出是这样的:

Jason Manford 已于 2013 年 8 月 10 日为 Comedy Gig 预订了房间 2。 Jack Coldrick Bill Gates Larry Page Jimmy Wales 将出席。

但是我想在参加事件的人的姓氏上加上一个和。我将如何去做这件事。我必须使用 List 吗？

非常感谢...

Answer 1

尝试将所选项目复制到另一个集合并使用一个简单的计数器:

int counter = 1; // start at 1 so that the counter is in line with the number of items that the loop has iterated over (instead of 0 which would be better for indexing into the collection)

List<ListItem> selectedItems = new List<ListItem>();

foreach (ListItem li in attendees.Items)
{
    if (li.Selected)
    {
        selectedItems.Add(li);
    }
}

foreach (ListItem li in selectedItems)
{
    counter++;

    if (selectedItems.Count > 1 && i == selectedItems.Count) // check after the counter has been incremented so that only the last item triggers it
    {
        people += " and";
    }

    people += li.Text + " ";
}

正如一些人所指出的，您还应该考虑使用 StringBuilder，因为字符串在 .Net 中是不可变的，这意味着它们不能被修改。每次将文本附加到字符串时，都会在幕后创建一个包含新内容的新字符串，并丢弃旧字符串。可以想象，如果列表中有很多名字，这最终可能会影响性能。示例如下:

List<ListItem> selectedItems = new List<ListItem>();

foreach (ListItem li in attendees.Items)
{
    if (li.Selected)
    {
        selectedItems.Add(li);
    }
}

StringBuilder sbPeople = new StringBuilder();
int counter = 1; // start at 1 so that the counter is in line with the number of items that the loop has iterated over (instead of 0 which would be better for indexing into the collection)

foreach (ListItem li in attendees.SelectedItems)
{
    counter++;

    if (selectedItems.Count > 1 && i == selectedItems.Count) // check after the counter has been incremented so that only the last item triggers it
    {
        sbPeople.Append(" and");
    }

    sbPeople.Append(li.Text);
    sbPeople.Append(" ");
}

引用 StringBuilder 文档:http://msdn.microsoft.com/en-us/library/system.text.stringbuilder.aspx