如何在 Blazor 中获得级联值？

Question

我有一个表单，其中用户首先 select 在下拉列表中选择一家公司，然后基于此他们可以从下拉列表中 select 一个项目。从数据库中查询的项目是基于用户和公司的。

我试图遵循一个较早的 post 关于级联下拉列表：https://www.mikesdotnetting.com/article/320/improved-cascading-dropdowns-with-blazor but this is rather old, and seems quite different from the current documentation. A lot has happened with Blazor in the last year. In reading the current official Blazor documentation (https://docs.microsoft.com/en-us/aspnet/core/blazor/components?view=aspnetcore-3.0#cascading-values-and-parameters）我看到他们有一个名为 "CascadingValue" 的 "HTML" 标签，这是正确的方法吗为我前进？如果可以，有人可以给我举一个如何做到这一点的例子吗？

<EditForm Model="@expense" Context="formContext" OnValidSubmit="@HandleValidSubmit">
                    <DataAnnotationsValidator />
                    <ValidationSummary />
<div style="float:left;width: 40%;">
                        <label asp-for="Client" class="control-label">Selskap</label>
                        <select asp-for="Client" class="form-control" @bind="@expense.Client">
                            <option></option>

                            @foreach (var ExpClient in cList)
                            {
                                <option selected="selected">
                                    @ExpClient.client
                                </option>
                                <option value="@ExpClient.client">@ExpClient.client</option>
                            }
                        </select>
                    </div>
                    <div style="clear:both;">&nbsp;</div>
                    <div style="float:left;width: 50%;">
                        <label asp-for="Project" class="control-label">Prosjekt</label>
                        <select asp-for="Project" class="form-control" @bind="@expense.Project">
                            <option></option>
                            @foreach (var ExpPro in ProList)
                            {
                                <option selected="selected">
                                    @ExpPro.Project
                                </option>
                                <option value="@ExpPro.Project">@ExpPro.Project</option>
                            }
                        </select>
                    </div>
</EditForm>

@code{

protected void GetExpProList()
    {
               ProList = objexpense.GetExpProList(userN).ToList();
    }
}

现在它只能根据用户名获取项目，这可行，但我还需要获取selected client，这样usernN和client都传递给查询DB的方法。

如果有人能在这里指出正确的方向，我将不胜感激。

编辑：根据我在此处获得的答案以及受 Mikesdotnetting (https://www.mikesdotnetting.com/article/320/improved-cascading-dropdowns-with-blazor) 的影响，我的解决方案最终看起来像这样：

        <InputSelect id="Client" class="form-control" @bind-Value="@expense.Client">
                        <option value=@(0)></option>

                        @foreach (var ExpClient in cList)
                {

                        <option value="@ExpClient.client">@ExpClient.client</option>
                }
                    </InputSelect>
                </div>
                @if (expense.Client != default ){
                <div style="clear:both;">&nbsp;</div>
                <div style="float:left;width: 50%;">

                    <label id="Project" class="control-label">Prosjekt</label>
                    <InputSelect id="Project" class="form-control" @bind-Value="@expense.Project">
                        <option value=@(0)></option>
                        @foreach (var ExpPro in objexpense.GetExpProList(userN,expense.Client).ToList())
                {

                        <option value="@ExpPro.Project">@ExpPro.Project</option>
                }
                    </InputSelect>
                </div>
                }

Answer 1

有一个名为 InputSelect 的组件，您可以将值绑定到该组件。

<InputSelect @bind-Value="selectedClient" class="form-control">
    @foreach (var ExpClient in cList)
    {
        <option value="@ExpClient.client">@ExpClient.client</option>
    }
</InputSelect>

第二个下拉菜单是这样的：

<InputSelect @bind-Value="selectedProject" class="form-control">
    @foreach (var ExpPro in objexpense.GetExpProList(userN, selectedClient).ToList())
    {
        <option value="@ExpPro.Project">@ExpPro.Project</option>
    }
</InputSelect>

如何在 Blazor 中获得级联值？

How can I get a cascading value in Blazor?

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