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Xamarin.UITesting NU1201 Error: Android 8.1 Is incompatible with .NETFramework 4.6.1

Have been having a little issue for the last couple of days now where I will create a new Xamarin Forms project on Visual Studio 2017 and add a Xamarin.UITest Cross-Platform Test Project for unit testing I recieve a series of NU1201 Errors when I reference the .Android App in the UITest Project.
Here is the exact error i get:
Error NU1201 Project App1.Android is not compatible with net461 (.NETFramework,Version=v4.6.1) / win-x64. Project App1.Android supports: monoandroid81 (MonoAndroid,Version=v8.1)
I have played around with the Android version numbers to see if the UITesting package doesnt support the latest android but no matter what version of android i target the problem remains the same.
Here is a screenshot of the project.
All the code is unchanged from the default project and runs in the simulator fine but only produces these errors when the Android app is referenced to the UITest project.

Solved it after many more hours of testing and trialling. Instead of adding the Android project to the references, Within the AppInitializer I added another method to the StartApp() call like so:
public class AppInitializer
{
public static IApp StartApp(Platform platform)
{
if (platform == Platform.Android)
{
return ConfigureApp.Android.InstalledApp("com.companyname.App1").StartApp();
}
return ConfigureApp.iOS.StartApp();
}
}
Therefore once I had already run the app via the emulator for the first time and installed on the device, the UITest simply uses the installed APK on the emulator instead of the project.

For those who ran into error NU1201, you might have come to the right place. This may not apply to the question asked but I ran into error NU1201 the other day and the reason for that is the nuproj configuration file for our nuget project has target configuration wrong. It should have been
<TargetFrameworkVersion>v4.6.2</TargetFrameworkVersion>
instead of
<TargetFramework>net462</TargetFramework>
because the project is not of "SDK-style."
References: https://learn.microsoft.com/en-us/visualstudio/msbuild/msbuild-target-framework-and-target-platform?view=vs-2019

WebApi controller tests method not found

I have a very simple WebAPI 2 controller running on .NET Framework 4.6.2, that looks like this:
[RoutePrefix("Invitations")]
public class InvitationsController : CqrsApiController
{
[HttpPost, Route("Clients/{id:long}/Actions/Cancel")]
public IHttpActionResult PostClientInvitationCancel(long id, [FromBody] ClientInvitationCancelCommand command)
{
Execute(command);
return SeeOther("Invitations/Clients/{0}", id);
}
}
and am trying to write an NUnit test for it, like this:
[TestFixture]
public class WhenExecutingAValidCommand
{
[Test]
public void ItShouldReturnARedirect()
{
var dispatcher = Substitute.For<ICqrsDispatcher>();
var urlHelper = Substitute.For<UrlHelper>();
urlHelper.Link(Arg.Any<string>(), Arg.Any<object>()).Returns("https://tempuri.org/");
var sut = new InvitationsController(dispatcher);
sut.Request = new HttpRequestMessage();
sut.Configuration = new HttpConfiguration();
sut.Url = urlHelper;
var response = sut.PostClientInvitationCancel(1, new ClientInvitationCancelCommand());
response.Should().BeOfType<SeeOtherRedirectResult>();
}
}
```
However, when I run the test, I get the following error:
System.MissingMethodException : Method not found: 'Void System.Web.Http.ApiController.set_Request(System.Net.Http.HttpRequestMessage)'.
at ApiProjectTests.InvitationsControllerTests.WhenExecutingAValidCommand.ItShouldReturnARedirect()
The same code seems to work fine in similar projects based on .NET Framework 4.5.1, so I'm wondering if there's some sort of DLL hell going on here. System.Web.Http is using Microsoft.AspNet.WebApi.Core.5.2.3, whereas System.Net.Http is coming from the GAC (well, C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\MSBuild\Microsoft\Microsoft.NET.Build.Extensions\net461\lib\System.Net.Http.dll to be more precise).
Update: if I try to debug into the unit test, the error occurs before I even enter the method. So although VS2017 compiles the tests just fine, when the test runner fires up, then everything falls apart. Sounds more like DLL hell to me.
Update 2: if I comment out the setting of the request, then I can debug into the test method. If I then put in a breakpoint, and then use the Immediate window to directly set the request property, it works, and there is no Method not found error. I also disabled Resharper and used VS2017's Test Explorer to run the tests, in case R# was caching something, but it made no difference.

It looks like my problem is indeed DLL hell, more specifically the DLL hell referenced by https://github.com/dotnet/corefx/issues/25773. The issue is caused by other NuGet packages that contain references to the newer version of System.Net.Http (4.2.0.0). The current solution appears to be to add a binding redirect to downgrade the assembly version to the expected version (4.0.0.0), but so far that has not helped me.
The solution that did work for me was to install the latest NuGet package of System.Net.Http, and use assembly binding redirects in my test project to ensure that it used the 4.2.0.0 version instead of 4.0.0.0.

This is often caused by early versions of nuget packages targeting .NET standard, which have dependencies on OOB ("out-of-band") packages. OOB packages are a kind of polyfill for dlls that are part of .NET framework but not .NET standard. Here is a very good explanation of what happened. In my case, the following helped:
I identified the nuget package that had a dependency on the system.net.http 4.2.0 nuget package, and upgrade that package.
The dependency was no longer present in the upgraded package, so i could uninstall the system.net.http 4.2.0 nuget package.
The upgraded package of course still expects the reference to the system.net.http 4.0.0 assembly, so in case of doubt, you may reinstall the upgraded package to make sure that the assembly reference is in your *.csproj file.

How to use iOS simulator/Android simulator from visual studio for Mac with xamarian.forms

I made mobile app at azure and quickstarted it as xamarian.forms and (after failing to publish downloaded table api application and deciding to edit it in browser) downloaded the client application they provided. Then when I tried to launch it with on (Debug>IPhone 8 Plus iOS 11.2) simulator, it (simulator) started but no application is visible (and nothing unusual is installed).
It shows warnings (could it be relevant?):
Warning MSB3276: Found conflicts between different versions of the same dependent assembly. Please set the "AutoGenerateBindingRedirects" property to true in the project file. For more information, see http://go.microsoft.com/fwlink/?LinkId=294190. (MSB3276)
(For Android simulator it gives some error like:
/Library/Frameworks/Mono.framework/Versions/5.4.1/lib/mono/xbuild/Microsoft/NuGet/Microsoft.NuGet.targets(5,5): Error: Your project is not referencing the "MonoAndroid,Version=v8.0" framework. Add a reference to "MonoAndroid,Version=v8.0" in the "frameworks" section of your project.json, and then re-run NuGet restore.
)
How can I see the ****** application?
Thank you. =)

Open the project.json file in your xxx.Droid project. Change the MonoAndroid version from:
"frameworks": {
"MonoAndroid,Version=v7.1": {}
}
to:
"frameworks": {
"MonoAndroid,Version=v8.0": {}
}
Now, Restore Nuget Packages for your solution.

The server factory could not be located for the given input: Microsoft.Owin.Host.HttpListener

I have implemente signalR in window service.
private IDisposable SignalR { get; set; }
public void Configuration(IAppBuilder app)
{
var hubconfig=new Microsoft.AspNet.SignalR.HubConfiguration();
hubconfig.EnableJSONP = true;
app.UseCors(CorsOptions.AllowAll);
app.MapSignalR(hubconfig);
}
private void StartSignalRServer(StringBuilder sbLog)
{
try
{
this.SignalR = WebApp.Start(ServerURI); //This throws exception
//this.SignalR= WebApp.Start<Startup>(ServerURI);
sbLog.Append(string.Format("{0}--------SignalR Server Started------",Environment.NewLine));
}
catch (Exception ex)
{
sbLog.Append(string.Format("{0}Exception in StartSignalRServer=>{1}", Environment.NewLine,ex.Message));
}
}
Exception:The server factory could not be located for the given input:
Microsoft.Owin.Host.HttpListener

The Microsoft.Owin.Host.HttpListener assembly is a runtime reference in WebApp.Start. You need to include it in the project's references for it to be available for loading. Check the bin\Debug (etc) directory to make sure it's included. May as well add it as a nuget dependency as well.

Install the package:
PM> Install-Package Microsoft.Owin.Host.HttpListener

Install the Microsoft.Owin.Host.HttpListener package from Nuget using:
PM> Install-Package Microsoft.Owin.Host.HttpListener
(unlike an earlier answer you should avoid using -IncludePrerelease in production code)

Hello for same error message but in slithly different context that i have encountered:
Due to stupid referencing optimization which is totally immature regarding reflection. It happens that MsBuild do not copies the Microsoft.Owin.Host.HttpListener.dll in your startup project if it references another project which uses Owin.
In my case I have the error messsage mentioned above and opted for explicit reference in project using Owin by adding explicit use of the problematic dll so that msbuild sees a reference needed so Microsoft.Owin.Host.HttpListener.dll will be copied (not needed for other dll) -This issue come from the fact that owin stuff does reflection inside itself leaving msbuild completely dummy by removing this dll-:
using Microsoft.Owin.Host.HttpListener;
...
_log.Debug("Loading type: "+ typeof(OwinHttpListener) + "..."); // Hack to force copy of Microsoft.Owin.Host.HttpListener.dll on target referencing project

I encountered same error.
In project A -- I am starting owin web service using WebApp.Start() in a function.
In Project B -- I am calling project A's function here. Unfortunately Project B is not my .Net solution's startup project.
Project C is my .Net Solution startup project.
If I Install nuget package using command Install-Package Microsoft.Owin.Host.HttpListener in solution's start up project i.e Project, C it works fine. If I do the same in Project B it does not work. So be careful while installing nuget package.

Execute MSI package in a custom Burn Bootstrapper Application

I am bundling a MSI package with the .NET 4.0 framework installer in Burn. Since i do not like the userinterface Burn applies, i have written my own custom Bootstrapper Application. The .NET framework is installed correctly, if it is not already installed. But i can not figure out how to install the MSI package. This is the code i have for my custom BA, i have checked that it gets executed.
public class ShopProtectBA : BootstrapperApplication
{
protected override void Run()
{
//Here i would like to run the bundled MSI package.
Engine.Quit(0);
}
}
The documentation on this is sparse. Should i not install the package in Run() ? How do this ting work?
Edit: I forgot to mention that is is a custom Managed Bootstrapper Application. If it makes any difference.
The best i can come up with is this:
var pl = new PlanMsiFeatureEventArgs("MyMsiPackage", "Complete", FeatureState.Local);
Engine.Detect();
OnPlanMsiFeature(pl);
Engine.Plan(LaunchAction.Install);
Engine.Elevate(FindWindow(null, "Setup"));
Engine.Apply(FindWindow(null, "Setup"));
But it results only in a window telling me that the installation is prepared. Then i closes and nothing more happends.

There's more to it than that: You have to ask the engine to detect machine state, plan package actions, and apply them. Take a look at the source code for the WiX BA itself: src\Setup\WixBA.