我遇到了编辑功能添加一个新条目而不是更新数据的问题，但是现在我更改了代码，它给了我如下错误：
object reference not set to an instance of an object
我已经尝试过返回视图模型，但是它仍然不能像更改存储库中的代码那样有效，但是仍然无法使它正常工作。我已经阅读了同一问题的一些答案，但是并不能解决我的问题。如果您仍然需要有关该程序的信息，请务必告诉我，谢谢！！
控制器：
//EDIT
[HttpGet]
public ActionResult Edit(int id)
{
var repo = new ManagementRepository();
var DVM = new DriverViewModel();
Driver editDriver = db.Drivers.Find(id);
// repo.UpdateDriver(editDriver);
return View(DVM);
}
[HttpPost]
public ActionResult Edit(DriverViewModel DVM)
{
var repo = new ManagementRepository();
var driver = new Driver();
using (var db = new VehicleReservationEntities())
{
var existingDriver = (from data in db.Drivers
where data.DriverID == DVM.DriverID
select data).FirstOrDefault();
existingDriver.DriverID = DVM.DriverID;
existingDriver.DriverLastName = DVM.DriverLastName;
existingDriver.DriverFirstName = DVM.DriverFirstName;
existingDriver.DriverLicense = DVM.DriverLicense;
existingDriver.LicenseExpiry = DVM.LicenseExpiry;
existingDriver.MobileNumber = DVM.MobileNumber;
existingDriver.BusinessUnit = DVM.BusinessUnit;
repo.UpdateDriver(existingDriver);
}
return View(DVM);
}
}
查看模型：
public class DriverViewModel
{
public int DriverID { get; set; }
public string DriverLastName { get; set; }
public string DriverFirstName { get; set; }
public string MobileNumber { get; set; }
public string DriverLicense { get; set; }
public Nullable<System.DateTime> LicenseExpiry { get; set; }
public string BusinessUnit { get; set; }
public bool IsActive { get; set; }
public System.DateTime DateRegistered { get; set; }
public string FullName
{
get { return DriverLastName + ", " + DriverFirstName; }
}
}
查看：
@model VehicleReservation.ViewModels.DriverViewModel
@{
ViewBag.Title = "Edit";
}
@section Jscripts{
<script type="text/javascript">
$(function () {
$("#LicenseExpiry").datepicker({
changeMonth: true,
changeYear: true,
format: "yyyy-MM-dd"
}
).datepicker("setDate", new DateTime());
});
</script>
<script src="@Url.Content("~/Scripts/jquery.validate.min.js")" type="text/javascript"></script>
<script src="@Url.Content("~/Scripts/jquery.validate.unobtrusive.min.js")" type="text/javascript"></script>
}
<h2>Edit Driver</h2>
<div class="row">
<div class="col-md-12 ">
<div class="panel" style="margin-top:3%; margin-bottom: 5%;">
<div class="panel-heading">
<div class="panel-title">
</div>
<div class="panel-body">
@using (Html.BeginForm())
{
@Html.AntiForgeryToken()
@Html.ValidationSummary(true, "", new { @class = "text-danger" })
@Html.HiddenFor(model => model.DriverID)
@Html.HiddenFor(model => model.DateRegistered) @Html.HiddenFor(model => model.DateRegistered)
@Html.HiddenFor(model => model.IsActive)
<div class="col-md-12">
<div class="col-md-4">
<div class="form-group">
<div class="form-group control-label">
<label>
Last Name
</label>
</div>
<div>
@Html.EditorFor(model => model.DriverLastName, new { htmlAttributes = new { @class = "form-control" } })
@Html.ValidationMessageFor(model => model.DriverLastName, "", new { @class = "text-danger" })
</div>
</div>
</div>
<div class="col-md-4">
<div class="form-group">
<div class="form-group control-label">
<label>
First Name
</label>
</div>
<div>
@Html.EditorFor(model => model.DriverFirstName, new { htmlAttributes = new { @class = "form-control" } })
@Html.ValidationMessageFor(model => model.DriverFirstName, "", new { @class = "text-danger" })
</div>
</div>
</div>
<div class="col-md-4">
<div class="form-group">
<div class="form-group control-label">
<label>
Mobile Number
</label>
</div>
<div>
@Html.EditorFor(model => model.MobileNumber, new { htmlAttributes = new { @class = "form-control" } })
@Html.ValidationMessageFor(model => model.MobileNumber, "", new { @class = "text-danger" })
</div>
</div>
</div>
</div>
<div class="col-md-12">
<div class="col-md-4">
<div class="form-group">
<div class="form-group control-label">
<label>
Driver's License
</label>
</div>
<div>
@Html.EditorFor(model => model.DriverLicense, new { htmlAttributes = new { @class = "form-control" } })
@Html.ValidationMessageFor(model => model.DriverLicense, "", new { @class = "text-danger" })
</div>
</div>
</div>
<div class="col-md-4">
<div class="form-group">
<div class="form-group control-label">
<label>
License Expiry
</label>
</div>
<div>
@Html.EditorFor(model => model.LicenseExpiry, new { htmlAttributes = new { @class = "form-control datepicker", @autocomplete = "off" } })
@Html.ValidationMessageFor(model => model.LicenseExpiry, "", new { @class = "text-danger" })
</div>
</div>
</div>
<div class="col-md-4">
<div class="form-group">
<div class="form-group control-label ">
<label>
Business Unit ID
</label>
</div>
<div>
@Html.EditorFor(model =>
model.BusinessUnit, new { htmlAttributes = new { @class = "form-control", @type = "text", @style = "width:50%" } })
@Html.ValidationMessageFor(model => model.BusinessUnit, "", new { @class = "text-danger" })
</div>
</div>
</div>
</div>
<div class="form-group">
<div class="col-sm-12">
<input type="submit" value="Save" class="btn btn-success" /> |
@Html.ActionLink("Back To List", "List", null, new { @class = "btn btn-primary btn-large" })
</div>
</div>
}
</div>
</div>
</div>
</div>
</div>
存储库：
public void UpdateDriver(Driver editDriver)
{
using (var db = new VehicleReservationEntities())
{
// var existingDriver = (from data in db.Drivers
// where data.DriverID == editDriver.DriverID
// select data).FirstOrDefault();
db.Entry(editDriver).State = EntityState.Modified;
db.SaveChanges();
}
/* using (var db = new VehicleReservationEntities())
{
db.Entry(id).State = EntityState.Modified;
db.SaveChanges();
}
*/
}
答案 0 :(得分：1)
Public Sub TestMe()
Dim arrColors As Variant
arrColors = Array(12, 2, 3, 4, 5) 'these are colors
Dim i As Long
For i = LBound(arrColors) To UBound(arrColors)
Worksheets(i + 1).Tab.ThemeColor = arrColors(i)
Next i
End Sub
如果数据库中没有具有该ID的驱动程序，则此行将返回“ null”。以后，这样做会导致空引用异常：
var existingDriver = (from data in db.Drivers
where data.DriverID == DVM.DriverID
select data).FirstOrDefault();