如何使用父项中的项ID来在子ListView中呈现相关项

I have a nested list view and the goal is to pull the ID from outer list view and pass it into the method below as the CurrentCategoryId This will allow my second list view to populate correctly. From what i read this should be done with a eventhandler OnItemDataBound but i am having trouble understanding how it that works?

我有一个嵌套列表视图，目标是从外部列表视图中提取ID并将其传递给下面的方法作为CurrentCategoryId这将允许我的第二个列表视图正确填充。从我读到的这应该用一个事件处理程序OnItemDataBound完成，但我很难理解它是如何工作的？

Please let me know if you have any questions

请让我知道，如果你有任何问题

<asp:ListView ID="ListView1"
    ItemType="E_Store_Template.Models.Category"
    runat="server"
    SelectMethod="GetCategories"
    OnItemDataBound="brandList_ItemDataBound">
    <ItemTemplate>
        <ul>
            <li style="list-style-type: none; text-align: left;">
                <b style="font-size: large; font-style: normal">
                    <a href="<%#: GetRouteUrl("ProductsByCategoryRoute", new {categoryName = Item.CategoryName}) %>">
                        <%#: Item.CategoryName %>
                    </a>
                    <asp:ListView ID="brandList" runat="server" ItemType="E_Store_Template.Models.Brand">
                        <ItemTemplate>
                            <ul style="list-style-type: none; text-align: left;">
                                <li>
                                    <a href="<%#: GetRouteUrl("ProductsByCatBrandRoute", new {brandName = Item.BrandName}) %>">
                                        <%#: Item.BrandName %>
                                    </a>
                                </li>
                            </ul>
                        </ItemTemplate>
                    </asp:ListView>
                </b>
            </li>
        </ul>
    </ItemTemplate>
</asp:ListView>

I think the event handler needs to look like this

我认为事件处理程序需要看起来像这样

protected List<Brand> brandList_ItemDataBound(object sender, ListViewItemEventArgs e)
{
    ListViewDataItem dataItem = (ListViewDataItem)e.Item;

    if (e.Item.ItemType == ListViewItemType.DataItem)
    {
        Category mydata = (Category)dataItem.DataItem;
        int CurrentCategoryId = mydata.CategoryID;
        var query = _db.Products.Where(p => p.Category.CategoryID == CurrentCategoryId).Select(p => p.Brand).Distinct();
        return query.ToList<Brand>();
    }
    else
    {
        return null;
    }
}

but gives me the error:

但是给了我错误：

'System.Collections.Generic.List<E_Store_Template.Models.Brand> E_Store_Template.SiteMaster.brandList_ItemDataBound(object, System.Web.UI.WebControls.ListViewItemEventArgs)' has the wrong return type

1 个解决方案

#1

ItemDataBound isn't designed to return data, it is designed to handle an event. In this case the event is rendering a category and anything that needs to happen as a child event. The proper course of action is to get the child ListView from the parent item and bind your data to it. Markup:

ItemDataBound不是为返回数据而设计的，它旨在处理事件。在这种情况下，事件将呈现一个类别以及需要作为子事件发生的任何事情。正确的做法是从父项中获取子ListView并将数据绑定到它。标记：

<asp:ListView ID="categoryList" runat="server"
    OnItemDataBound="brandList_ItemDataBound" ItemType="E_Store_Template.Models.Category" SelectMethod="GetCategories">
        <LayoutTemplate>
            <ul style="list-style-type: none;">
                <asp:PlaceHolder runat="server" ID="itemPlaceholder" />
            </ul>
        </LayoutTemplate>
        <ItemTemplate>
            <li style="text-align: left;">
                <b style="font-size: large; font-style: normal">
                    <a href="<%#: GetRouteUrl("ProductsByCategoryRoute", new {categoryName = Item.CategoryName}) %>">
                        <%#: Item.CategoryName %>
                    </a>
                </b>
                <asp:ListView ID="brandList" runat="server">
                    <LayoutTemplate>
                        <ul style="list-style-type: none; text-align: left;">
                            <asp:PlaceHolder runat="server" ID="itemPlaceholder" />
                        </ul>
                    </LayoutTemplate>
                    <ItemTemplate>
                        <li>
                            <a href="<%#: GetRouteUrl("ProductsByCatBrandRoute", new {brandName = Item.BrandName}) %>">
                                <%#: Item.BrandName %>
                            </a>
                        </li>
                    </ItemTemplate>
                </asp:ListView>
            </li>
        </ItemTemplate>
    </asp:ListView>

Code behind:

代码背后：

protected void brandList_ItemDataBound(object sender, ListViewItemEventArgs e)
{
    ListViewDataItem dataItem = (ListViewDataItem)e.Item;

    if (e.Item.ItemType == ListViewItemType.DataItem)
    {
        Category mydata = (Category)dataItem.DataItem;

        int CurrentCategoryId = mydata.CategoryID;
        var query = _db.Products.Where(p => p.Category.CategoryID == CurrentCategoryId).Select(p => p.Brand).Distinct();

        ListView brandList = (ListView)e.Item.FindControl("brandList");
        brandList.DataSource = query.ToList<Brand>();
        brandList.DataBind();
    }
}

I added LayoutTemplates with PlaceHolders so your ListView doesn't repeat your tags for each record. I also moved your closing tag because you shouldn't have a block element (unordered list) as a child of a bold tag set.

我在PlaceHolders中添加了LayoutTemplates，因此ListView不会为每条记录重复标记。我还移动了你的结束标记，因为你不应该有一个块元素（无序列表）作为粗体标记集的子元素。

I would consider getting all the Categories and Brands in 1 (or 2) SQL queries then filtering the Brands data list by the appropriate CategoryID. You would store the Brands data list as a page level variable, but don't load it into Session or ViewState, you only need it during the page rendering.

我会考虑在1（或2）个SQL查询中获取所有类别和品牌，然后通过适当的CategoryID过滤品牌数据列表。您可以将Brands数据列表存储为页面级变量，但不要将其加载到Session或ViewState中，只需在页面呈现期间将其加载。