I am having issues with Platform Effects in Xamarin Forms. These effects worked in a shared library format, and we are now migrating to .NET Standard 2.0 for reasons outside of the scope of this post.
Project Setup
VS 2017 15.8.0
Xamarin Forms 3.1.0.697729
Two .Net Standard 2.0 projects (one is for components, the other for the main UI)
Two Android projects (one that runs, the other is an Android .dll)
Two iOS projects (same deal)
Main Issue
None of my platform effects in the Android .dll work. They all resolve as null effect.
According to the documentation, my setup is correct. (Documentation here)
I found two different issues and have hit a brick wall.
When I follow the instructions exactly and place [assembly: ResolutionGroupName("MyGroupName")] on the platform renderer itself, I get exceptions with Xamarin's dependency resolver. There is no message, just an exception and stack trace that leads back to the constructor of the RoutingEffect.
When I use a slightly different pattern and register that on the namespace of an empty file in my .NET Standard 2.0 project, all effects return as null effect.
I've been Googling and digging through forums to no avail. Does anyone have an idea what could be the problem?
Side notes: All of the custom renderers work after using the static Init() trick, but not the effects. I have also tried making the typeof() statement reference both the Android version of the class and the .NET Standard 2.0 version of the class.
For the sake of completeness, here's what I have going.
NET Standard 2.0:
namespace MyBaseNamespace.Components.Effects
{
public class SearchBarStylingEffect : RoutingEffect
{
public SearchBarStylingEffect() : base("MyGroupName.SearchBarStylingEffect")
{
}
}
}
Android:
[assembly: ResolutionGroupName("MyGroupName")]
[assembly: ExportEffect(typeof(SearchBarStylingEffect), "SearchBarStylingEffect")]
namespace MyBaseNamespace.Components.Android.Renderers.Effects
{
public class SearchBarStylingEffect : PlatformEffect
{
…
}
}
(iOS is the same as Android, only the namespace is different)
I also posted this on Xamarin's forums, and Billy Liu from Xamarin asked a question that ultimately led me down the right path. I'll link to that here and also post what fixed it.
link: Xamarin Forms Post
Here's the resolution from that post:
In short, I had to do the following things to get this functional
(which it now is):
Ensure that the GroupNameResolution tag was on the first Effect ever initialized in the app.
Remove the empty file initializer from my .Net 2.0 project.
???
Profit.
Related
Trying to use Prism 8, ContainerLocator, IHttpClientFactory and Platform-Specific Service registration with DryIoc Extensions (not Magician) in a Xamarin Forms application
I have these nuget packages installed
Prism.DryIoc.Extensions
Prism.Forms
My main Xamarin Application inherits from PrismApplicationBase.
In platform code (eg Android) I have IPlatformInitializer implented by MainActivity and for platform-specific services I use:
LoadApplication(new App(this));
as documented here:
https://prismlibrary.com/docs/dependency-injection/platform-specific-services.html
This line causes the IContainerExtension to be resolved in the shared code
protected override IContainerExtension CreateContainerExtension()
...but I can't find a way to successfully return a valid IContainerExtension implementation.
I've attempted:
https://prismlibrary.com/docs/dependency-injection/container-locator.html
var createContainerExtension = () => new DryIocContainerExtension();
ContainerLocator.SetContainerExtension(createContainerExtension);
But the code given here can't even compile - the DryIocContainerExtension class created is defined INTERNAL and isn't available to my application code.
If I use...
PrismContainerExtension.Init();
or
return ContainerLocator.Current;
...as worked previously (eg Prism 7.2) I get a runtime error as described here:
https://githubmemory.com/repo/dansiegel/Prism.Container.Extensions/issues/180
ValueFactory attempted to access the Value property of this instance.
Please can someone advise what I'm doing wrong, or do I have to get my company to pay for Magician to resolve my issue?
So I was jsut wondering why in the Prism Doc and VS template this line is included in the App Class.
public App() : this(null) { }
Since today I commented it out and the App still started without any issues in both iOs and Android.
Best Regards
Basecrusher
If you don't need/want an IPlatformInitializer, it's fine to pass null, and the default implementation does so.
I guess the code is in there to remind you that you could pass an IPlatformInitializer if you needed/wanted to.
"With Xamarin.Forms you may have read how you can add the Dependency attribute for an impelementing type in your Platform Specific code and then resolve it with the Xamarin.Forms DependencyService. This is considered a major Anti-Pattern that should be avoided when you are using a proper Dependency Injection container. It is for this reason that Prism has dropped all support for working with the DependencyService as of Prism 7.0. Starting with Prism 6.3 the IPlatformInitializer was introduced. This allows you to easily register types with Prism's container."
https://prismlibrary.com/docs/xamarin-forms/dependency-injection/platform-specific-services.html
I have my UWP Application inherited from Base class, which inherits from MvxApplication<Setup, CoreApp>:
public sealed partial class App : WindowsApplication
{
public App()
{
InitializeComponent();
}
}
public class WindowsApplication : MvxApplication<Setup, CoreApp>
{
}
public class Setup : MvxWindowsSetup<CoreApp>
{
public override IEnumerable<Assembly> GetViewAssemblies()
{
// need to do this as otherwise I receive the message that corresponding view to view model is not found
var assemblies = base.GetViewAssemblies().ToList();
assemblies.Add(typeof(Forms.App).Assembly);
return assemblies;
}
}
However, when launching it, receiving the following error message:
The type MvxContentPagePresentationAttribute is not configured in the
presenter dictionary
As I understand, all that is not proper way to launch Xamarin.Forms MvvmCross application, as UWP App and Setup should be inherited from something like MvxFormsApplication and MvxFormsWindowsSetup<CoreApp, Forms.App> respectively (to have Xamarin.Forms app properly initialized).
But:
MvxFormsApplication is not generic and doesn't provide ability of passing Forms-generic setup.
even if I inherit the App from MvxFormsApplication and use this.RegisterSetupType<MvxFormsWindowsSetupInheritor>();, Visual Studio compiler never allows me to compile the project because of some weird error message (something like The name “WindowsApplication” does not exist in the namespace “…”) (this might be some issue of Visual Studio, but I have VS 15.7 version, which expects the code to work (again, MvvmCross declares they support UWP and XF)).
So, from my understanding, if there is Xamarin.Forms app, there must be also some way of passing actually Xamarin.Forms App class to the UWP App class initialization.
MvvmCross, again, stands for UWP and Xamarin.Forms support, but I can't see any clear example of the way to setup such type of application.
MvvmCross documentation as always is quite "modest". There are some instructions about setting up MvvmCross UWP app as well as setting up MvvmCross XF iOS/Android, but the only word about MvvmCross XF UWP is:
You are now free to place your custom renderers in a different
assembly. All you have to do to make it work is to add your assembly
to the Setup.ViewAssemblies collection.
(in official website docs)
(which is still sounds weird, as iOS and Android versions don't need that additional code, which makes me think that such (current) documentation isn't quite actualized)
and
UWP, WPF
Extend App from MvxApplication. ( App : MvxApplication { } )
from MvvmCross.Forms package readme.txt file, when all other platforms, again, expect inheritance for the app classes from MvxForms*-based ones.
MvvmCross guys, any thoughts on that?
When I set up a new Xamarin.Forms project, I always follow the Playground sample in the MvvmCross GitHub as this example evolves along with the API and is always up-to-date, as it is part of the MvvmCross solution, so any commits need to preserve its functionality. So if you want to see how everything should look in a minimal UWP + Xamarin.Forms project see the Playground.Forms.UI and Playground.Forms.Uwp projects in the linked folder.
I've got two questions here. The first one is just specific and another one is more general, but is a source of the first one.
So, my specific problem: I want to use Encryption (actually, Hashing) algorithms with using System.Security.Cryptography namespace (for instance, SHA256Managed class).
I found out that (happily) Xamarin has implemented those in System.dll.
But it is not portable and obviously can not be used from Core application directly.
But I've also found another great project -- PclContrib -- which allows you to do that. But, unfortunately, they don't have the implementation for Touch and Android. (However, that still works great for Desktop (Web) and Windows Phone, plus, still can be included into Core (as it uses portable project)).
Anyway, to solve that nicely, I've decided to create some base class for the encryption methods and then override core methods which require the custom dll (for any custom system).
The way I did it (at least, trying to do) was:
Defining virtual method in Core App base class:
public virtual IEncryptionProvider CreateEncryptionProvider()
Overriding Core App class in Touch project with overriding CreateEncryptionProvider (which creates an instance of TouchEncryptionProvider class instance).
Core:
public class App : MvxApplication
Touch:
public class AppTouch : App
Launching it in Touch setup.cs:
protected override Cirrious.MvvmCross.ViewModels.IMvxApplication CreateApp (
{
return new AppTouch();
}
But, that does not work for me. On startup I've got this exception message in log:
"Exception masked KeyNotFoundException: Could not find view for Mynamespace.Etc.LoginViewModel", which works fine when I do new App() instead. I am not sure if that message shows actual problem (as before it was saying the same even that was a problem with some third-party dll, unrelated to views at all). But speaking shortly, that's just a primitive inheritance of App : MvxApplication, but placed not in Core but Touch project.
So, does it requeire some more custom initialization for such situations or do I miss something else?
And, actually, more general question is how should I build such Multiplatform approaches? Actually, now I've got similar problem with HttpUtility.UrlEncode, which I would want to use in my Core project.
What is the MvvmCross "philosophy" to handle such situations?
Thank you.
For the 'viewmodel not found' problem, this is caused because mvvmcross by default only looks for viewmodels in the Assembly containing your app.
If you want it to look in other assemblies, override ViewModelAssemblies in Setup.cs - see how this done in, for example, MvvmCross - structuring shared View Models and Views
For general multplatform approach, please read questions and answers like:
Platform-specific IoC in MVVMCross
Instantiation of ViewModels and Service classes
Please also remember you don't have to use PCLs - if you prefer to use file-linking between multiple platform-specific core projects, then you can of course use this approach.
Finally, please also try to ask one question per question - I find it makes stackoverflow work better for users and with search engines too. If you need to link questions, then you can just add a hyperlink reference - stackoverflow then marks them as related.
I've upgraded MVC3 from RC2 to RTM. We were using Ninject 2.1.0.76, but things stopped working once I upgraded. So I used the NuGet manager to get the latest Ninject, Ninject.MVC3 and Ninject.Web.Mvc libraries (2.1.0.91, 1.0.0.0 and 2.1.0.39 respectively). Now, it creates an AppStart_NinjectMVC3 file.
I removed NinjectHttpApplication from my global.asax and made it back into a regular HttpApplication. When I tried to build, I get;
"Exception has been thrown by the target of an invocation"
Looking further, if I disable the following line;
DependencyResolver.SetResolver(new NinjectServiceLocator(kernel));
The build goes through. But I'm pretty sure I don't want to do this.
Any ideas?
----- UPDATE ---------
I created a new MVC3 project, added the reference to Ninject.MVC3 and this builds and runs fine. I compared web.config, don't see any differences that relate to Ninject or MVC in the two. A fresh project doesn't add the Ninject.Web.Mvc library, so I removed it and commented out all code relating to that, and still, the error occurs.
Since ASP.NET MVC 3 Beta the IServiceLocator interface is replaced by IDependencyResolver. I'm not sure Ninject.MVC3 already has a release where they have implemented this interface.
Judging from the line DependencyResolver.SetResolver(new NinjectServiceLocator(kernel)) it appears they have not.
Here's a simple implementation of this interface for Ninject.
UPDATE: The Ninject.Web.Mvc library has a NinjectDependencyResolver class that extends from the IDependencyResolver interface. I think you should use this one (I do and everything works fine).
Download the dlls from here
https://github.com/ninject/ninject/archives/master
https://github.com/ninject/ninject.web.mvc/archives/master
Further more do not use Ninject.MVC3 all you need ist Ninject.Web.Mvc
I also have an article documenting same here