I have an MVC application that uses dynamic business objects that inherit from the parent type of an object. For example, a base class Clientcan have two subclasses of Vendorand ServiceProvider, and all of them are handled by the same controller. I have a partial view that I load on the right side of the page when viewing client details called _Aside.cshtml. When I download the client, I try to search for a specific version first and cannot load the general one. Below is the code code.
@try
{
@Html.Partial("_" + Model.Type.TypeName + "Aside")
}
catch (InvalidOperationException ex)
{
@Html.Partial("_Aside")
}
The TypeName property will contain the word "Provider" or "ServiceProvider" in it.
Now this works fine, but the problem is that I only want it to fail, if the view is not found, it also fails when there is an actual InvalidOperationExceptionone deduced by the partial view (usually the result of a child action it can call). I thought about checking with Exception.Message, but it seems a bit hacky. Is there any other way to get the desired result without checking the property Messageor is this my only option at this point?
ex.Message = "The partial view '_ServiceProviderAside' was not found or no view
engine supports the searched locations. The following locations were
searched: (... etc)"
The UPDATE . This is a class with extension methods that I have in my project based on Jack's answer, as well as Chao's suggestion.
public static class ViewExtensionMethods
{
public static bool PartialExists(this HtmlHelper helper, string viewName)
{
if (string.IsNullOrEmpty(viewName)) throw new ArgumentNullException(viewName, "View name cannot be empty");
var view = ViewEngines.Engines.FindPartialView(helper.ViewContext, viewName);
return view.View != null;
}
public static bool PartialExists(this ControllerContext controllerContext, string viewName)
{
if (string.IsNullOrEmpty(viewName)) throw new ArgumentNullException(viewName, "View name cannot be empty");
var view = ViewEngines.Engines.FindPartialView(controllerContext, viewName);
return view.View != null;
}
public static MvcHtmlString OptionalPartial(this HtmlHelper helper, string viewName)
{
return PartialExists(helper, viewName) ? helper.Partial(viewName) : HtmlString.Empty;
}
public static MvcHtmlString OptionalPartial(this HtmlHelper helper, string viewName, string fallbackViewName)
{
return OptionalPartial(helper, viewName, fallbackViewName, null);
}
public static MvcHtmlString OptionalPartial(this HtmlHelper helper, string viewName, object model)
{
return PartialExists(helper, viewName) ? helper.Partial(viewName, model) : MvcHtmlString.Empty;
}
public static MvcHtmlString OptionalPartial(this HtmlHelper helper, string viewName, string fallbackViewName, object model)
{
return helper.Partial(PartialExists(helper, viewName) ? viewName : fallbackViewName, model);
}
public static void RenderOptionalPartial(this HtmlHelper helper, string viewName)
{
if (PartialExists(helper, viewName))
{
helper.RenderPartial(viewName);
}
}
public static void RenderOptionalPartial(this HtmlHelper helper, string viewName, string fallbackViewName)
{
helper.RenderPartial(PartialExists(helper, viewName) ? viewName : fallbackViewName);
}
}
. ASP.NET Core MVC, PartialExists() HtmlHelper IHtmlHelper . , ASP.NET Core
public static class ViewExtensionMethods
{
public static bool PartialExists(this IHtmlHelper helper, string viewName)
{
var viewEngine = helper.ViewContext.HttpContext.RequestServices.GetService<ICompositeViewEngine>();
if (string.IsNullOrEmpty(viewName)) throw new ArgumentNullException(viewName, "View name cannot be empty");
var view = viewEngine.FindView(helper.ViewContext, viewName, false);
return view.View != null;
}
public static bool PartialExists(this ControllerContext controllerContext, string viewName)
{
var viewEngine = controllerContext.HttpContext.RequestServices.GetService<ICompositeViewEngine>();
if (string.IsNullOrEmpty(viewName)) throw new ArgumentNullException(viewName, "View name cannot be empty");
var view = viewEngine.FindView(controllerContext, viewName, false);
return view.View != null;
}
public static bool PartialExists(this ViewContext viewContext, string viewName)
{
var viewEngine = viewContext.HttpContext.RequestServices.GetService<ICompositeViewEngine>();
if (string.IsNullOrEmpty(viewName)) throw new ArgumentNullException(viewName, "View name cannot be empty");
var view = viewEngine.FindView(viewContext, viewName, false);
return view.View != null;
}
}
...
@Html.OptionalPartial("_" + Model.Type.TypeName + "Aside", "_Aside")
//or
@Html.OptionalPartial("_" + Model.Type.TypeName + "Aside", "_Aside", Model.AsideViewModel)