我遇到了这个错误，我检查的值不是null。当我尝试按下“保存”按钮时出现此错误。
请帮帮我，这是错误：
The parameter conversion from type 'System.String' to type 'ULIV.ViewModels.NewProposal' failed because no type converter can convert between these types.
ModelState.IsValid为false。
以下是使用的视图模型：
public class PurchaseOrderViewModel
{
[Key]
public int ID { get; set; }
public IEnumerable<Institution> Institution { get; set; }
[Required]
public string PurchaseOrderNo { get; set; }
[Required]
public DateTime PurchaseOrderDate { get; set; }
[Required]
public DateTime ReceivedDate { get; set; }
public string Remarks { get; set; }
public IEnumerable<NewProposal> Proposal { get; set; }
public IEnumerable<PODetail> PODetail { get; set; }
public IEnumerable<NewProposal> AddedProposal { get; set; }
}
这是控制器动作：
[HttpPost]
public ActionResult Create(PurchaseOrderViewModel purchaseorderviewmodel)
{
purchaseorderviewmodel.AddedProposal = (List<ULIV.ViewModels.NewProposal>)Session["AddedProposal"];
//purchaseorderviewmodel.Proposal = db.NewProposal.Where(x => x.Status.StatusID == 3).ToList();
int instituionId = Convert.ToInt32(Session["InstitutionID"]);
purchaseorderviewmodel.Institution = db.Institutions.Where(x => x.InstitutionID == instituionId).ToList();
if (ModelState.IsValid)
{
db.PurchaseOrderViewModels.Add(purchaseorderviewmodel);
db.SaveChanges();
return RedirectToAction("Index","Fulfillment");
}
ViewBag.Proposal = new SelectList(db.NewProposal.Where(x => x.Status.StatusID == 3), "ProposalID", "ProposalCode");
return View(purchaseorderviewmodel);
}
此外，这些是即时窗口上的值：
((List<ULIV.ViewModels.NewProposal>)Session["AddedProposal"]).FirstOrDefault()
DateModified: {1/15/2014 2:57:52 PM}
FinalUnitPrice: 23
FinalVolume: 34
getdatestring: "1/15/2014"
Institution: {System.Data.Entity.DynamicProxies.Institution_B01649AB79941CE0188D081B425698F4FD6629E82FDB13CCE17B03E348459273}
InstitutionID: 1
Product: {ULIV.Models.ProductModel}
ProductID: 1
ProposalCode: "PC-2014-00001"
ProposalID: 1
ProposedUnitPrice: 3
ProposedVolume: "2"
RelatedProposalCode: ""
Remarks: "hello"
Status: {ULIV.Models.Status}
StatusID: 3
VaccineType: {ULIV.Models.VaccineType}
VaccineTypeID: 1
((List<ULIV.ViewModels.NewProposal>)Session["AddedProposal"]).FirstOrDefault()
这是视图：
<div class="row">
@using (Html.BeginForm("Create", "PurchaseOrder",
new { ReturnUrl = ViewBag.ReturnUrl },
FormMethod.Post, new { @class = "form-horizontal" }))
{
@Html.AntiForgeryToken()
@Html.ValidationSummary(true)
<h1 class="subpage-headline font-global">New Purchase Order</h1>
<div class="row">
<h2 class="subpage-headline2 font-global">New Purchase Order</h2>
@*<form class="form-horizontal" role="form">*@
@foreach (var inst in Model.Institution)
{
<div class="row-div">
<div class="form-group">
<label class="col-sm-2 control-label">Institution Name:</label>
<div class="col-sm-3">
<label class="control-text-label">@Html.DisplayFor(modelItem => inst.InstitutionName)</label>
</div>
</div>
<div class="form-group">
<label class="col-sm-2 control-label">Account Classifications:</label>
<div class="col-sm-3">
<label class="control-text-label">Private</label>
</div>
</div>
<div class="form-group">
<label class="col-sm-2 control-label">Employee Population:</label>
<div class="col-sm-3">
<label class="control-text-label">50</label>
</div>
</div>
</div>
<div class="row-div">
<div class="form-group">
<label class="col-sm-2 control-label">Address:</label>
<div class="col-sm-4">
<label class="control-text-label">Ninoy Aquino Ave. Clark Pampanga Clark Freeport Zone 1500</label>
</div>
</div>
<div class="form-group">
<label class="col-sm-2 control-label">Telephone No.:</label>
<div class="col-sm-3">
<label class="control-text-label">599-3146</label>
</div>
</div>
</div>
}
@*</form>*@
@*<form class="form-horizontal" role="form">*@
<div class="form-group">
<label class="col-sm-2 control-label">Purchase Order Number:</label>
<div class="col-sm-4">
@Html.TextBoxFor(model => model.PurchaseOrderNo, new { @class = "form-control", @type = "text" })
</div>
</div>
<div class="form-group">
<label class="col-sm-2 control-label">Purchse Order Date:</label>
<div class="col-sm-4">
@Html.TextBoxFor(model => model.PurchaseOrderDate, new { @class = "form-control datepicker", @type = "text" })
</div>
</div>
<div class="row">
<label class="col-sm-2"></label>
<label class="col-sm-2 font-md">Proposal Code <span class="required">*</span></label>
<label class="col-sm-2 font-md">Description <span class="required">*</span></label>
<label class="col-sm-2 font-md">Unit Price w/ VAT <span class="required">*</span></label>
<label class="col-sm-1 font-md">Total Units <span class="required">*</span></label>
<label class="col-sm-2 font-md">Total Amount w/ VAT <span class="required">*</span></label>
<label class="col-sm-1"></label>
</div>
<div class="form-group">
<label class="col-sm-2 control-label">Proposal:</label>
<div class="col-sm-2">
@Html.DropDownList("ProposalID", new SelectList(ViewBag.Proposal, "Value", "Text"), "SELECT Proposal", new { @class = "form-control input", @type = "text", @name = "ddlInst" })
</div>
<div class="col-sm-2">
<input type="text" class="form-control" id="prodDesc_0">
</div>
<div class="col-sm-2">
<input type="text" class="form-control" id="unitPrice_0">
</div>
<div class="col-sm-1">
<input type="text" class="form-control" id="totalUnits_0">
</div>
<div class="col-sm-2">
<input type="text" class="form-control" id="totalAmount_0">
</div>
<div class="col-sm-1">
<button type="button" class="btn btn-primary" onclick="AddProposal()">Add</button>
</div>
</div>
<div class="form-group">
<label class="col-sm-2 control-label">Product:</label>
<div class="col-sm-9">
<table class="table table-bordered table-hover">
<thead>
<tr class="th-center">
<th>Proposal Code</th>
<th>Description</th>
<th>Unit Price VAT</th>
<th>Total Units</th>
<th>Total Amount w/ VAT</th>
<th>Action</th>
</tr>
</thead>
<tbody>
@Html.HiddenFor(model => model.AddedProposal)
@if (Model.AddedProposal != null)
{
foreach (var prop in Model.AddedProposal)
{
<tr class="text-center">
<td>@Html.DisplayFor(modelItem => prop.ProposalCode)</td>
<td>@Html.DisplayFor(modelItem => prop.Product.Description)</td>
<td>@Html.DisplayFor(modelItem => prop.FinalUnitPrice)</td>
<td>@Html.DisplayFor(modelItem => prop.FinalVolume)</td>
<td>3875.75</td>
<td class="text-center">
<a href="#">
<img src="../../Images/icon_delete.png" width="16" height="16"></a>
</td>
</tr>
}
}
@if (Model.AddedProposal == null)
{
}
</tbody>
</table>
</div>
</div>
<div class="form-group">
<label class="col-sm-2 control-label">Received Date:</label>
<div class="col-sm-4">
@Html.TextBoxFor(model => model.ReceivedDate, new { @class = "form-control datepicker", @type = "text" })
</div>
</div>
<div class="form-group">
<label class="col-sm-2 control-label">Remarks:</label>
<div class="col-sm-4">
@Html.TextBoxFor(model => model.Remarks, new { @class = "form-control", @type = "text" })
</div>
</div>
@*</form>*@
</div>
<div class="row col-xs-offset-2" style="padding-top: 30px;">
<button type="submit" class="btn btn-primary">Save</button>
<button type="button" class="btn btn-primary" onclick="window.location='@Url.Action("Index", "Fulfillment")'">Cancel</button>
</div>
}
请帮助这是我第一次遇到这种错误。我不确定错误是否来自“”
答案 0 :(得分：7)
GOT IT！
我刚删除了这行代码：
@Html.HiddenFor(model => model.AddedProposal)
答案 1 :(得分：1)
我刚刚发现了这个错误的非常原因。
public async Task<ActionResult> Add(string m = null) { }
[HttpPost]
public async Task<ActionResult> Add(FooViewModel m) { }
在Get方法中我有一个可选的string m = null参数，同时，Post方法当然传入了模型。好吧，因为在这种情况下我也命名了变量m，那是是什么导致了这个错误丑陋，也许是一个错误？
答案 2 :(得分：0)
对我而言，它引用了type而不是field。我所拥有的是：
Html.DropDownListFor(m => m.SiteExtendedAttributeValues[0] etc.
我把它改为：
Html.DropDownListFor(m => m.SiteExtendedAttributeValues[0].SiteExtendedAttributeDefinitionId
错误消失了。
答案 3 :(得分：-1)
Session["AddedProposal"]中可能存在字符串值，因此当您尝试将其显式转换为NewProposal时会出现错误