if / else 语句 ASP.NET C#

Question

截至目前，我正在尝试创建一个 ASP.NET 页面，该页面将根据您选择的类别按钮在列表框中列出一个类别中的书籍，然后我还有另外两个按钮（一个用于 DESC 顺序，一个用于ASC 订单）。现在的问题是，当我在点击虚构按钮并填充列表框后单击 ASC 或 DESC 按钮时，它会擦除​​列表框并将我返回到 pageload 事件。

我已经尝试将填充项目移动到页面加载事件，当我一切正常时，但由于某种原因，当通过其他按钮点击它时它就不起作用了。

我是 ASP.NET 的新手，非常欢迎简单或“对新手友好”的解释和代码示例/修复！

提前致谢！

代码如下

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class partin : System.Web.UI.Page
{
private List<String> books = new List<String>();

public void Page_PreRender()
{
    Item_Listbox.DataSource = books;
    Item_Listbox.DataBind();
}

int SortASC(string x, string y)
{
    return String.Compare(x, y);
}

int SortDESC(string x, string y)
{
    return String.Compare(x, y) * -1;
}

protected void Page_Load(object sender, EventArgs e)
{
    Header_Label.Text = "Welcome! Please select a book category.";


}



protected void Fiction_Click(object sender, EventArgs e)
{
    Header_Label.Text = "Fiction Section";

    books.Add("Title: The Old Man and The Sea | Decription: An epic novel. | Price: 10 USD | Quantity: 3");
    books.Add("Title: A Game of Thrones | Decription: A tale of fire and ice. | Price: 15 USD | Quantity: 6");
    books.Add("Title: Dracula | Decription: A book about vampires. | Price: 5 USD | Quantity: 7");
    books.Add("Title: Twilight | Decription: An awful book. | Price: Free | Quantity: 1000");  

}


protected void Non_Fiction_Click(object sender, EventArgs e)
{
    Header_Label.Text = "Non-Fiction Section";



}
protected void Self_Help_Click(object sender, EventArgs e)
{
    Header_Label.Text = "Self Help Section";



}

protected void Sort_Command(object sender, CommandEventArgs e)
{
    if (e.CommandName == "Sort")
    {
        switch (e.CommandArgument.ToString())
        {
            case "ASC":
                books.Sort(SortASC);
                break;
            case "DESC":
                books.Sort(SortDESC);
                break;
        }
    }
}



}

编辑：感谢您的帖子，它不再直接返回页面加载事件并在标签中保持更改为“小说”，但当我单击 ASD 或 DESC 按钮时，它仍在重置 ListBox 中的数据.

Answer 1

您需要检查这是否是您的 Page_Load 中的回发：

if(!IsPostBack){
  Header_Label.Text = "Welcome! Please select a book category";
  //put your prerender logic in here, too...to populate the list of books.
}

Page_Load 每次都会触发。您通常将页面初始化逻辑放在那里，但对于回发（如按钮单击），您不希望重新运行该初始代码。因此，检查页面是否处于回发状态 (IsPostback==true);如果不是，则初始化页面。否则，让页面在回发期间根据 ViewState 中存储的内容呈现。

Answer 2

尝试将 Page_PreRender 中的代码放入 Page_Load 中

protected void Page_Load(object sender, EventArgs e)  
{  
    if (!IsPostBack)
    {
        Header_Label.Text = "Welcome! Please select a book category.";  

        Item_Listbox.DataSource = books;  
        Item_Listbox.DataBind();  
    }  
}

对于排序方法添加数据绑定

protected void Sort_Command(object sender, CommandEventArgs e)   
{   
    if (e.CommandName == "Sort")   
    {   
        switch (e.CommandArgument.ToString())   
        {   
            case "ASC":   
                books.Sort(SortASC);   
                break;   
            case "DESC":   
                books.Sort(SortDESC);   
                break;   
        }   
    }  
    Item_Listbox.DataSource = books;  
    Item_Listbox.DataBind();  
}   

Answer 3

检查页面加载和排序命令修改事件

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class partin : System.Web.UI.Page
{
private List<String> books = new List<String>();

public void Page_PreRender()
{
    Item_Listbox.DataSource = books;
    Item_Listbox.DataBind();
}

int SortASC(string x, string y)
{
    return String.Compare(x, y);
}

int SortDESC(string x, string y)
{
    return String.Compare(x, y) * -1;
}

protected void Page_Load(object sender, EventArgs e)
{
if(!IsPostBack){

    Header_Label.Text = "Welcome! Please select a book category.";
    Item_Listbox.DataSource = books;
    Item_Listbox.DataBind();

}

}



protected void Fiction_Click(object sender, EventArgs e)
{
    Header_Label.Text = "Fiction Section";

    books.Add("Title: The Old Man and The Sea | Decription: An epic novel. | Price: 10 USD | Quantity: 3");
    books.Add("Title: A Game of Thrones | Decription: A tale of fire and ice. | Price: 15 USD | Quantity: 6");
    books.Add("Title: Dracula | Decription: A book about vampires. | Price: 5 USD | Quantity: 7");
    books.Add("Title: Twilight | Decription: An awful book. | Price: Free | Quantity: 1000");  

}


protected void Non_Fiction_Click(object sender, EventArgs e)
{
    Header_Label.Text = "Non-Fiction Section";



}
protected void Self_Help_Click(object sender, EventArgs e)
{
    Header_Label.Text = "Self Help Section";



}

protected void Sort_Command(object sender, CommandEventArgs e)
{
    if (e.CommandName == "Sort")
    {
        switch (e.CommandArgument.ToString())
        {
            case "ASC":
                books.Sort(SortASC);
                break;
            case "DESC":
                books.Sort(SortDESC);
                break;
        }
    }
    Item_Listbox.DataSource = books;  
    Item_Listbox.DataBind();  
}

}