如果/ else语句ASP.NET C＃

Question

截至目前，我正在尝试创建一个ASP.NET页面，该页面将列出来自类别的书籍，列表框中的基于您选择哪个类别的按钮，然后我有另外两个按钮（一个用于DESC订单，另一个用于ASC订单）。现在的问题是，当我点击小说按钮并点击了ASC或DESC按钮并填充列表框时，它将清除列表框并将我引回页面加载事件。

我已经尝试将填充项移动到页面加载事件，并且当我拥有所有内容时都工作得很完美，但由于某种原因，通过其他按钮点击时它不起作用。

我对ASP.NET非常陌生，非常欢迎所以这么简单或“新手友好”的解释和代码示例/修复程序！

在此先感谢！

下面的代码

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：谢谢你的职位，不再径直回到了页面加载事件，并保持在标签的变化说“小说”，但它仍然是正在重置的数据当我点击ASD或DESC按钮时列表框。

Answer 1

你需要检查，如果这是一个回发或不是在你的Page_Load：

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

的Page_Load触发每次。您通常会将页面初始化逻辑放在那里，但对于回发（如按钮单击），您不希望重新运行初始代码。因此，如果页面处于回发状态（IsPostback == true），请在该处进行检查;如果不是，则初始化页面。否则，根据存储在ViewState中的内容让页面在回发期间呈现。

Answer 2

检查页面加载和sort命令修改的事件

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(); 
} 

} 

Answer 3

尝试把代码Page_PreRender在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(); 
    } 
} 

和排序，metjhod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(); 
}