下拉不工作MVC C＃剃刀

Question

我有一個頁面，有3個下拉列表，客戶，項目和設施。 當第一次加載頁面時，我可以將這些值加載到數據庫的下拉列表中。

更改客戶端中的選定值應該基於所選客戶端加載新項目，改變所選項目的相同方式應加載屬於選定項目的新設施。

當我更改客戶端值時，項目和設施加載正常，甚至認爲所選客戶端未顯示在下拉列表中。但是當我改變項目或設施似乎沒有發生時，所有選定的值都會返回0。 這裏是CSHTML代碼

@using (Html.BeginForm("Index", "Home")) { 
    @Html.DropDownListFor(x => x.SelectedClientId, new SelectList(Model.Clients, "PrimaryKey", "Name", Model.SelectedClientId), "--Select Client--", new { onchange = "this.form.submit();" }); 
} 
@using (Html.BeginForm("Index", "Home")) { 
    @Html.DropDownListFor(y => y.SelectedProjectId, new SelectList(Model.Projects, "PrimaryKey", "Name", Model.SelectedProjectId), "--Select Project--", new { onchange = "this.form.submit();" }) 
} 
@using (Html.BeginForm("Index", "Home")) { 
    @Html.DropDownListFor(z => z.SelectedFacilityId, new SelectList(Model.Facilities, "PrimaryKey", "Name", Model.SelectedFacilityId), "--Select Facility--", new { onchange = "this.form.submit();" }) 
} 

這裏是IndexViewModel

public class IndexViewModel { 
    public int SelectedClientId { get; set; } 
    public BusinessEntityCollection<Client> Clients { get; set; } 

    public int SelectedProjectId { get; set; } 
    public BusinessEntityCollection<Project> Projects { get; set; } 

    public int SelectedFacilityId { get; set; } 
    public BusinessEntityCollection<Facility> Facilities { get; set; } 
} 

這裏是HomeController的

public ActionResult Index(IndexViewModel model) { 

BusinessEntityCollection<Client> clients = new BusinessEntityCollection<Client>(); 
BusinessEntityCollection<Project> projects = new BusinessEntityCollection<Project>(); 
BusinessEntityCollection<Facility> facilities = new BusinessEntityCollection<Facility>(); 

clients = ClientController.GetClients(); 

if (Request.HttpMethod == "POST") { 
    Session["SelectedClientId"] = model.SelectedClientId; 
    Session["SelectedProjectId"] = model.SelectedProjectId; 
    Session["SelectedFacilityId"] = model.SelectedFacilityId; 

    if (Session["SelectedClientId"] == null) { 
     projects.Add(new Project() { Name = "None", PrimaryKey = 0 }); 
    } 
    else { 
     if (Convert.ToInt32(Session["SelectedClientId"]) == 0) { 
      projects = ProjectController.GetUserProjects(clients[0].PrimaryKey); 
      Session["SelectedClientId"] = clients[0].PrimaryKey; 
     } 
     else 
      projects = ProjectController.GetUserProjects(Convert.ToInt32(Session["SelectedClientId"])); 
    } 

    if (Session["SelectedProjectId"] == null) { 
     facilities.Add(new Facility() { Name = "None", PrimaryKey = 0 }); 
    } 
    else { 
     if (Convert.ToInt32(Session["SelectedProjectId"]) != 0) 
      facilities = FacilityController.GetFacilitiesByProject(Convert.ToInt32(Session["SelectedProjectId"])); 
    } 
} 

model.Clients = clients; model.Projects = projects; model.Facilities = facilities; 
return View(model); 

}

我想選擇的值保存到會話變量和檢索他們，但它似乎並沒有工作。

Answer 1

對於所有三個下拉菜單，您都需要一個表單。並非每種形式。

@using (Html.BeginForm("Index", "Home")) { 
    @Html.DropDownListFor(x => x.SelectedClientId, new SelectList(Model.Clients, "PrimaryKey", "Name", Model.SelectedClientId), "--Select Client--", new { onchange = "this.form.submit();" }); 

    @Html.DropDownListFor(y => y.SelectedProjectId, new SelectList(Model.Projects, "PrimaryKey", "Name", Model.SelectedProjectId), "--Select Project--", new { onchange = "this.form.submit();" }) 

    @Html.DropDownListFor(z => z.SelectedFacilityId, new SelectList(Model.Facilities, "PrimaryKey", "Name", Model.SelectedFacilityId), "--Select Facility--", new { onchange = "this.form.submit();" }) 
}