我现在有一个删除对象的问题,本周早些时候这段代码工作正常,但现在我得到一个空引用异常,即使我试图删除的对象,以及实体框架的实例不是空的.
MHNHubEntities _entities = new MHNHubEntities();
// Get,GetList,Add,Save etc.
public void Delete(PackageProduct packageProduct)
{
_entities.PackageProducts.DeleteObject(packageProduct);
}
packageProduct是一个有效的packageProduct,除此删除之外的所有其他内容都有效.通常我不会问如何解决空引用异常 – 因为它非常明显,检查空值.然而 – 在这种情况下,我很难过,昨天突然发生的事情不是,这就是抛出异常的原因.任何帮助将不胜感激,我已经确认抛出此异常时不涉及空对象.
编辑
我不想排除某些东西是空的并导致这种情况 – 因为抛出异常的本质.根据请求,这里是堆栈跟踪：
at MHNHub.Areas.Store.Controllers.SettingsController.DeletePackage(Int32 id,FormCollection collection) in C:\Users\Grahame\Desktop\Projects\MHN Hub\Visual Studio Project\MHNHub\MHNHub\Areas\Store\Controllers\SettingsController.cs:line 618 at lambda_method(Closure,ControllerBase,Object[] ) at System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller,Object[] parameters) at System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext,IDictionary`2 parameters) at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext,ActionDescriptor actionDescriptor,IDictionary`2 parameters) at System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClassd.<InvokeActionMethodWithFilters>b__a() at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter,ActionExecutingContext preContext,Func`1 continuation)
继承我的控制器动作：
[HttpGet]
public ActionResult DeletePackage(int id,FormCollection collection)
{
try
{
IPackageRepository packageRepository = new PackageRepository();
var package = packageRepository.GetPackage(id);
IPackageProductRepository packageProductRepository = new PackageProductRepository();
var packageProducts = package.PackageProducts.ToList();
foreach (var packageProduct in packageProducts)
{
packageProductRepository.Delete(packageProduct);
}
packageRepository.Delete(package);
packageRepository.Save();
return Json(new { Success = "true" },JsonRequestBehavior.AllowGet);
}
catch (Exception ex)
{
//return JSON with exception
var result = new { Message = ex.Message,InnerException = ex.InnerException.ToString() };
return Json(result,JsonRequestBehavior.AllowGet);
}
}
解决方法
好吧,如果它正在这条线上：
_entities.PackageProducts.DeleteObject(packageProduct);
并假设这不是由于内联DeleteObject(即错误实际存在于那里),那么NullReferenceException只有两个可能的原因：
> _entities为null
> _entities.PackageProducts为null
如果这种情况可重复发生,应该很容易找出它是什么：
public void Delete(PackageProduct packageProduct)
{
var x = _entities;
if (x == null)
{
throw new Exception("_entities was null");
}
var y = x.PackageProducts;
if (y == null)
{
throw new Exception("_entities.PackageProducts was null");
}
y.DeleteObject(packageProduct);
}
(当然,仅用于诊断目的.)
