Question

到目前为止，我正在尝试创建一个ASP.NET页面，它将根据您选择的类别按钮在列表框中列出类别中的书籍，然后我有另外两个按钮（一个用于DESC订单，一个用于ASC订单）。现在的问题是，当我点击小说按钮并填充列表框后点击ASC或DESC按钮时，它会擦除列表框并将我回到pageload事件。

我已经尝试将填充项目移动到pageload事件，当我的所有内容都完美无缺时，但由于某种原因，当通过其他按钮单击它时，它将无法正常工作。

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

提前致谢！

以下代码

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：感谢帖子，它不再直接回到pageload事件并保持标签中的更改说“Fiction”但是当我点击ASD或DESC按钮时它仍然在重置ListBox中的数据。

Answer 1

您需要检查这是否是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每次都会开火。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），您不希望重新运行初始代码。如果页面处于回发状态（IsPostback == true），那么请检查一下;如果不是，则初始化页面。否则，让回页期间的页面根据ViewState中存储的内容进行渲染。

Answer 2

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();  
}

}

Answer 3

尝试将Page_PreRender中的代码放在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();  
    }  
}

并为sort-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();  
}

如果是/ else语句ASP.NET C＃

3 个答案: