如何使用 Webforms 在 Asp.net 中按产品类型对产品进行分类

Question

我想使用下拉列表按类型对产品进行排序。

当我在下拉列表中 select 按类型分类的产品不起作用。

ProductByType 的存储过程：

Public List<Product> GetProductsByType(int typeId)
    {
        try
        {
            using (GarageDBEntities db = new GarageDBEntities())
            {
                //select * from table where condition is required type
                List<Product> products = (from x in db.Products
                                          where x.TypeId == typeId
                                          select x).ToList();
                return products;
            }
        }
        catch (Exception)
        {
            return null;
        }
    }

用于显示产品的索引页代码：

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

public partial class Index : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        FillPage();
    }

    private void FillPage()
    {
        //Get a lsit of all products in DB
        ProductModel productModel = new ProductModel();
        List<Product> products = productModel.GetAllProducts();

        //Make sure products exists in the database
        if (products != null)
        {
            //Create a new Panel with an ImageButton and 2 labels for each Product
            foreach (Product product in products)
            {
                Panel productPanel = new Panel();
                ImageButton imageButton = new ImageButton();
                Label lblName = new Label();
                Label lblPrice = new Label();

                //Set childControls properties
                imageButton.ImageUrl = "~/Images/Products/" + product.Image;
                imageButton.CssClass = "productImage";
                imageButton.PostBackUrl = "~/Pages/Product.aspx?id=" + product.Id;

                lblName.Text = product.Name;
                lblName.CssClass = "productName";

                lblPrice.Text = "₹" + product.Price;
                lblPrice.CssClass = "productPrice";

                //Add child controls to Panel
                productPanel.Controls.Add(imageButton);
                productPanel.Controls.Add(new Literal { Text = "<br />" });
                productPanel.Controls.Add(lblName);
                productPanel.Controls.Add(new Literal { Text = "<br />" });
                productPanel.Controls.Add(lblPrice);

                //Add dynamic Panels to static Parent panel
                pnlProducts.Controls.Add(productPanel);
            }
        }
        else
        {
            //No products found
            pnlProducts.Controls.Add(new Literal { Text = "No Products Found!" });
        }
    }

    protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {
        ProductModel productModel = new ProductModel();
        List<Product> products = productModel.GetProductsByType(Convert.ToInt32(DropDownList1.SelectedItem.Value));

            foreach (Product product in products)
            {
                Panel productPanel = new Panel();
                ImageButton imageButton = new ImageButton();
                Label lblName = new Label();
                Label lblPrice = new Label();

                //Set childControls properties
                imageButton.ImageUrl = "~/Images/Products/" + product.Image;
                imageButton.CssClass = "productImage";
                imageButton.PostBackUrl = "~/Pages/Product.aspx?id=" + product.Id;

                lblName.Text = product.Name;
                lblName.CssClass = "productName";

                lblPrice.Text = "₹" + product.Price;
                lblPrice.CssClass = "productPrice";

                //Add child controls to Panel
                productPanel.Controls.Add(imageButton);
                productPanel.Controls.Add(new Literal { Text = "<br />" });
                productPanel.Controls.Add(lblName);
                productPanel.Controls.Add(new Literal { Text = "<br />" });
                productPanel.Controls.Add(lblPrice);

                //Add dynamic Panels to static Parent panel
                pnlProducts.Controls.Add(productPanel);
            }
    }
}

即使我 select 产品类型，它也总是显示所有产品。如图所示，我 select 编辑了“Engine Oil”，但它显示了所有产品。我希望它仅显示在下拉列表中选择的 selected 产品类型的特定产品。

Answer 1

尝试在您的 Page_Load 事件中添加 PostBack 验证：

C#代码：

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

最有可能的是，当在下拉列表中选择一个项目时，会生成一个回发，它将调用 PageLoad 并重新加载所有产品，为避免这种情况，通常设置回发验证

确保在 <asp:DropDownList /> 控件中使用 AutoPostBack="True" 标志

如何使用 Webforms 在 Asp.net 中按产品类型对产品进行分类

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