Nick's .NET Travels

Continually looking for the yellow brick road so I can catch me a wizard....

Debugging Not Working for .NET Standard library in UWP Application

I was attempting to debug some code in a .NET Standard library that was being referenced from a Xamarin.Forms base UWP application. Unfortunately, it didn’t matter where I set the breakpoint in the library, they were never hit. Initially I thought that this was related to it being a multi-targeted project but it turns out this same issue applies to a regular .NET Standard library.

The only hint I had was when the application was running there was a yellow warning triangle on my breakpoint which a pretty unhelpful, yet accurate, message.

image

Now you’d have thought that since this project was included in the same solution as the application, that it was being built by Visual Studio as part of building and running the application, that you wouldn’t have to do anything special to get step through debugging to work. This is not the case – it appears that debug symbols can’t be loaded – huh! I mean seriously, we expect better.

I had also recently installed the first preview of Visual Studio 2017 15.9 so I thought that might be the issue but no, even opening it in 15.8 still showed the same issue.

So it turns out that there is an issue with the default build configuration – open project properties for the .NET Standard library and click on Advanced under the Build tab

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The default “Debugging information” value of Portable is what the issue is. Change this to Full or Pdb-only

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Doing this will set the debugging settings for the currently selected target framework and platform. For example for my project it generated:

<PropertyGroup Condition="'$(Configuration)|$(TargetFramework)|$(Platform)'=='Debug|netstandard2.0|AnyCPU'">
   <DebugType>pdbonly</DebugType>
   <DebugSymbols>true</DebugSymbols>
</PropertyGroup>

I simplified this so that it would always use these debugging settings when doing a Debug build

<PropertyGroup Condition="'$(Configuration)'=='Debug'">
   <DebugType>pdbonly</DebugType>
   <DebugSymbols>true</DebugSymbols>
</PropertyGroup>

And there you have it – step through debugging should now work. I’m not sure why it’s so hard for Visual Studio to either use this option by default, or at least provide a useful warning that directs the developer to either documentation, or actually switches the setting automatically.

Getting Started with Xamarin.Forms, Refactoring MvvmCross and Services

Previous posts in this sequence:
Getting Started with Xamarin.Forms and Multi-Targeting in Visual Studio
Getting Started with Xamarin.Forms and SDK Versions
Getting Started with Xamarin.Forms with MvvmCross
Getting Started with Xamarin.Forms and Authenticating with ADAL

In this post I’m going to do a bit of a refactor based on the work completed in the previous post where we added code directly into the MainViewModel to use the Azure Active Directory Authentication Library. This would be fine if the MainViewModel was the only view model in the application that needed access to the Authenticate method. As I will probably want to make use of it elsewhere, I’ve decided to refactor that code into a class called CredentialService.

When I wired up MvvmCross a couple of posts ago, I did so without going into much detail on how the relationship between view models and their corresponding page is setup. I’m not going to delve into the inner workings of MvvmCross but suffice to say that there is some reflection magic that goes on based on the names of the classes. A view model with the name MainViewModel will be paired with a page called MainPage.

In addition to the magic that glues the view model and pages together (and thus the navigation model) MvvmCross also has a quite powerful dependency injection framework. The CredentialService that I’ll be creating will be registered with the DI framework as a singleton that can be easily accessed.

Let’s start by creating the CredentialService and it’s corresponding interface ICredentialService in a folder called Services in the Core library.

public partial class CredentialService:ICredentialService
{
     private const string AuthEndpoint = "
https://login.microsoftonline.com/{0}/oauth2/token";

    private const string ResourceId = "https://graph.windows.net/";
     private const string TenantId = "[your tenantId]";
     private const string ClientId = "[your clientId]";
     private const string RedirectURI = "[your redirectURI]";

    public string AccessToken { get; set; }

    public async Task<string> Authenticate()
     {
         string authority = string.Format(CultureInfo.InvariantCulture, AuthEndpoint, TenantId);
         var authContext = new AuthenticationContext(authority);

        var result = await authContext.AcquireTokenAsync(ResourceId, ClientId, new Uri(RedirectURI), this.PlatformParameters);
         AccessToken = result.AccessToken;
         return AccessToken;
     }
}

public interface ICredentialService
{
     Task<string> Authenticate();
}

The platform specific code will need to be extracted out of the MainViewModel.Platform.cs into the corresponding CredentialService.Platform.cs. For example the UWP class would be:

public partial class CredentialService
{
     private IPlatformParameters PlatformParameters => new PlatformParameters(PromptBehavior.Always, false);
}

In order to register the CredentialService with the DI framework, we just need to add a small bit of code to the Initialize method of the App class in the Core library

public override void Initialize()
{
     CreatableTypes()
         .EndingWith("Service")
         .AsInterfaces()
         .RegisterAsLazySingleton();

    RegisterAppStart<MainViewModel>();
}

The last step is to make use of the service in the MainViewModel. We do this by adding a parameter of type ICredentialService to the MainViewModel constructor.

private ICredentialService CredentialService { get; }
public MainViewModel(ICredentialService credentialService)
{
     CredentialService = credentialService;
}

private async Task Authenticate()
{
     Debug.WriteLine(await CredentialService.Authenticate());
}

And that’s it – we haven’t changed any functionality but the solution is better organised and structured in a way that services can easily be added without cluttering up view models.

image

Getting Started with Xamarin.Forms and Authenticating with ADAL

Previous posts in this sequence:
Getting Started with Xamarin.Forms and Multi-Targeting in Visual Studio
Getting Started with Xamarin.Forms and SDK Versions
Getting Started with Xamarin.Forms with MvvmCross

Now that we’ve got the basics of an application, we’re going to add some authentication using the Azure Active Directory Authentication Library. We’re going to start with registering an application with Azure Active Directory (AAD) (the docs do cover this here but I figured I’d cover it again anyway). Start by heading over to the Azure portal and selecting Azure Active Directory from the set of tabs on the left.

image

In the list of tabs for the AAD, find the App Registrations tab

image

Click “New application registration” and fill in the details for the new app

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Note that the Sign-on URL doesn’t have to be a real URL, just one that both the portal and the app know about – we’ll use this later! After you’re done creating the app registration you should be able to retrieve the Application ID. Save this information for later as we’ll need it when we’re authenticating the user within our application.

image

The pieces of information you’ll need in order to use ADAL within your application are:

clientId – This is the Application ID that was displayed after you created the app registration in the Azure portal. This is a GUID

redirectUri – This is the Redirect URI that you specified when creating the app registration. If you didn’t write this down, or you want to double check, or change it, you can do so by clicking the Redirect URIs tab under Settings for the app registration. This is a URL (e.g. https://stratapark)

resourceId – This is the identifier of the resource you want to access. In this case we just want to authenticate the user, so we’re going to use the default resource, which is the AAD directory itself, https://graph.windows.net/. This can be a URL or a GUID depending on the type of resource you’re referencing

tenantId – This is the identifier of the tenant that you’re authenticating against. This can be the URL or GUID of your tenant.

To retrieve the tenantId you need to select the Properties tab of the Azure Active Directory and copy the Directory ID

imagehttps://www.nuget.org/packages/Microsoft.IdentityModel.Clients.ActiveDirectory/

Now that we’ve setup the app registration, we’re good to start writing some code. Firstly, we need to add a reference to the ADAL library from NuGet – search for Microsoft.IdentityModel.Clients.ActiveDirectory

image

Add the ADAL library to all projects.

Let’s start with the UI and add a button to the MainPage.

<Button Text="Authenticate" Command="{Binding AuthenticateCommand}" />

And of course we need a command within the MainViewModel. In fact we’ll add the bulk of the authentication code to the MainViewModel too:

private IMvxCommand authenticateCommand;
public IMvxCommand AuthenticateCommand => authenticateCommand ?? (authenticateCommand = new MvxAsyncCommand(Authenticate));

private const string AuthEndpoint = "https://login.microsoftonline.com/{0}/oauth2/token";

private const string ResourceId= "https://graph.windows.net/";
private const string TenantId = "[your tenantId]";
private const string ClientId = "[your clientId]";
private const string RedirectURI = "[your redirectUri]”;

public async Task Authenticate()
{
     string authority = string.Format(CultureInfo.InvariantCulture, AuthEndpoint, TenantId);
     var authContext = new AuthenticationContext(authority);

    var result = await authContext.AcquireTokenAsync(ResourceId, ClientId, new Uri(RedirectURI), PlatformParameters);
     Debug.WriteLine( result.AccessToken);
}

The only thing missing is the PlatformParameters (bolded in the code above). As the name suggests, these are platform specific parameters required by the ADAL library. For each platform we need to expose a property that returns an IPlatformParameters within the MainViewModel.Platform.cs for each platform.

Android

private IPlatformParameters PlatformParameters => new PlatformParameters(CurrentActivity, true, PromptBehavior.Auto);
public Activity CurrentActivity
{
     get
     {
         var top = Mvx.IoCProvider.Resolve<IMvxAndroidCurrentTopActivity>();
         return top.Activity;
     }
}

iOS

private IPlatformParameters PlatformParameters => new PlatformParameters(GetTopViewController(),true, PromptBehavior.Auto);
public static UIViewController GetTopViewController()
{
     var window = UIApplication.SharedApplication.KeyWindow;
     var vc = window.RootViewController;
     while (vc.PresentedViewController != null)
         vc = vc.PresentedViewController;

    if (vc is UINavigationController navController)
         vc = navController.ViewControllers.Last();

    return vc;
}

UAP

private IPlatformParameters PlatformParameters => new PlatformParameters(PromptBehavior.Always, false);

NetStandard

private IPlatformParameters PlatformParameters => null;

Note: you need to provide the NetStandard implementation otherwise the NetStandard target won’t build.

There is one more thing we need to add. Android requires an additional piece of code within the Activity that hosts the Xamarin.Forms application

protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
{
     base.OnActivityResult(requestCode, resultCode, data);
     AuthenticationAgentContinuationHelper.SetAuthenticationAgentContinuationEventArgs(requestCode, resultCode, data);
}

If your Android application authenticates but doesn’t ever return the access token, chances are that your OnActivityResult override is either missing, or on the wrong Activity – I spent a bit of time trying to work out why iOS and UWP worked but Android would just hang; turns out I was missing this override.

There you have it – you’re good to go with using ADAL to authenticate your users within your Xamarin.Forms application

Getting Started with Xamarin.Forms with MvvmCross

Previous posts in this sequence:

Getting Started with Xamarin.Forms and Multi-Targeting in Visual Studio

Getting Started with Xamarin.Forms and SDK Versions

Next up is adding in MvvmCross – no surprises here: Add the MvvmCross package to all projects in the solution

image

We need to make a few adjustments to the Core library. First up, we need to add an App class to Core that inherits from MvxApplication. For the moment the only thing this class is going to do is to set the initial view model of the application. One of the core ideas behind MvvmCross is that navigation is driven from view models, rather than at the view level. By setting the initial view model, we’re effectively defining which view will be shown when our application launches.

public class App : MvxApplication
{
     public override void Initialize()
     {
         RegisterAppStart<MainViewModel>();
     }
}

We’ll do a bit of tidying up whilst we’re making changes to the Core project. We’ll create a ViewModels folder and move MainViewModel into folder

We’ll update MainViewModel and MainViewModel.Platform.cs (all four) to add ViewModels to namespace. We’ll also update MainViewModel to inherit from MvxViewModel.


Now that we’ve updated the Core library, we’ll turn our attention to the UI library and the head projects. We’ll add the MvvmCross.Forms NuGet reference to all projects, except Core.

image

The only other change we need to make to the UI library for the moment is to update MainPage to inherit from MvxContentPage instead of ContentPage. You’ll need to do this in both the xaml and xaml.cs files. However, I would recommend dropping the inheritance from the xaml.cs file as it is not required in multiple places.


Next up we need to adjust each of the head projects (UWP, iOS and Android) so that they use MvvmCross to launch the Xamarin.Forms views.

UWP

Rename MainPage to HostPage (in both MainPage.xaml and MainPage.xaml.cs, and the filenames themselves) in the UWP head project – we do this to avoid any confusion between the name of the page and any views that are automatically associated with MainViewModel. Also update HostPage to inherit from MvxFormsWindowsPage.

For UWP we need an additional step due to some limitation around the support for generics. Add a help class ProxyMvxApplication, defined as follows:

public abstract class ProxyMvxApplication : MvxWindowsApplication<MvxFormsWindowsSetup<Core.App, UI.App>, Core.App, UI.App> { }

Change App.xaml and App.xaml.cs to inherit from ProxyMvxApplication, and remove all code in App.xaml.cs other than the constructor which should contain a single call to InitializeComponent. Override the HostWindowsPageType method in the App class

protected override Type HostWindowsPageType()
{
     return typeof(HostPage);
}

Build and run the UWP application

iOS

Update the AppDelegate as follows

public partial class AppDelegate : MvxFormsApplicationDelegate<MvxFormsIosSetup<Core.App, UI.App>, Core.App, UI.App>
{ }

Build and run the iOS application.

Android

Rename and update the MainActivity as follows. Again, we rename the activity to avoid confusion with any activity or view that would be automatically associated with MainViewModel.

public class HostActivity
         : MvxFormsAppCompatActivity<MvxFormsAndroidSetup<Core.App, UI.App>, Core.App, UI.App>
{ }

Build and run the Android application.

You may experience a build error when you attempt to build and run the Android application, relating to referencing the Mono.Android.Export library. In this case, use the Add Reference dialog to manually add the missing reference.

image


There you have it – all three platforms running Xamarin.Forms application powered by MvvmCross.

Getting Started with Xamarin.Forms and SDK Versions

In my previous post I did a walk through of creating a new Xamarin.Forms application and setting up the Core and UI projects for multi-targeting. Whilst I covered updating the various NuGet packages, I didn’t look at the SDK versions for the three platforms. In this post I’m going to look at the options for setting the SDK version, as it’s important that you update this to target the latest SDK version, even if your application is going to support older platform versions.

Android

If you right-click on the Android head project and select Properties you’ll see the Project Properties pane.

Start by increasing the Target Framework by selecting the highest Android version that you have installed

image

Next, on the Android Manifest tab, select “Use Compile using SDK version” under the Target Android version. On this tab you can also set the Minimum Android version if you don’t want to accept the defaults – this may be relevant if you don’t want a massive support matrix for your application as it will prevent installation on devices running a version of Android older than the minimum.

image

Build and run the Android application to make sure you haven’t broken anything and then commit your changes – in this case the first change would have made changes to the Android csproj file, whereas the second change would have changed the AndroidManifest.xml file.

iOS

Setting the SDK Version for iOS is straight forward and the recommendation is to leave the “Default” (which should be the default value) in the SDK Version dropdown on the iOS Build tab on the Properties pane for the iOS application.

image

If you want to adjust the minimum supported version of iOS, you can do this by double-clicking the Info.plist file for your iOS application and then adjusting the Deployment Target.

image


UWP

Both the Target and Min version of the UWP application can be set from the Application tab of the Project Properties pane. Setting the Target version defines the SDK version that will be used to compile the application and thus the APIs that are available.

image


Core and UI

Now that the Core and UI libraries are set to be multi-targeted it is also necessary to define what the target framework/version should be for each platform. If you don’t do this, you may be limited as to what platform APIs are available. Rather than setting these values in each of the libraries, we can create a file, Directory.build.targets, in the solution folder and include the appropriate elements there – this will get included in all projects that support the new csproj format. In this case the contents of our Directory.build.targets file will look like

<Project>
   <PropertyGroup Condition="$(TargetFramework.StartsWith('netstandard'))">
     <DefineConstants>$(DefineConstants);NETSTANDARD;PORTABLE</DefineConstants>
   </PropertyGroup>
   <PropertyGroup Condition="$(TargetFramework.StartsWith('uap'))">
     <DefineConstants>$(DefineConstants);NETFX_CORE;XAML;WINDOWS;WINDOWS_UWP</DefineConstants>
     <TargetPlatformVersion>10.0.17134.0</TargetPlatformVersion>
     <TargetPlatformMinVersion>10.0.16299.0</TargetPlatformMinVersion>
   </PropertyGroup>
   <PropertyGroup Condition="$(TargetFramework.StartsWith('Xamarin.iOS'))">
     <DefineConstants>$(DefineConstants);MONO;UIKIT;COCOA;IOS</DefineConstants>
   </PropertyGroup>
   <PropertyGroup Condition="$(TargetFramework.StartsWith('MonoAndroid'))">
     <DefineConstants>$(DefineConstants);MONO;ANDROID</DefineConstants>
   </PropertyGroup>
</Project>

The csproj for both Core and UI projects also needs to be updated to replace the target framework MonoAndroid81 with MonoAndroid90.

All your projects should now be targeting the latest framework/sdk versions. If you find that some, or all, of these changes don’t take effect, you may need to either reload specific projects, or restart Visual Studio.

Getting Started with Xamarin.Forms and Multi-Targeting in Visual Studio

I’ve walked through this a couple of times in the past (last year and in the Mvx+1 series I started) but I wanted to do an updated post to firstly point out that the getting started process in Visual Studio has stabilized quite a lot and the process of getting a new Xamarin.Forms project up and running is quite smooth. The second thing I wanted to add is how, and why, you can setup your .NET Standard libraries to be multi-targeted – this also has come a long way.

Note: I’m running Visual Studio 15.8 preview 5, so your experience may vary a little if you’re running a different version of Visual Studio. Before I get started I try to make sure all my components are up to date, including my MacMini which is what I use for building/debugging iOS applications.

Let’s get started by creating a new solution within Visual Studio, using the Mobile App (Xamarin.Forms) project template

image

This will prompt you to select what template to use, in this case we’re going to create a project based on a Blank template. In actual fact this template isn’t blank; it has 1 page which is required in order for the application to build and run. Also, make sure you select the .NET Standard Code Sharing Strategy. DO NOT select Shard Project – this options in my opinion should now be deprecated as multi-targeting is a much better option for achieving this same outcome.

image

After clicking OK to create the project, you’ll want to make sure you can successfully build all projects.

Next open the NuGet package manager for the solution and update all packages to the latest stable. In my case I just had to update Microsoft.NETCore.UniversalWindowsPlatform and Xamarin.Forms.

Now, make sure that each platform (i.e. iOS, Android and UWP) compiles and runs. Technically you don’t need to do this but if you run into difficulty later, at least doing a run check here gives you a “last known good” state to revert to. On that note, after checking that each platform runs, I would be making the initial commit to source control for your solution.

Next we’re going to add a new project based on the Class Library (.NET Standard) project template. This will be our Core project that will contain all our view models, services and business logic for the application.

image

The new project will come with Class1. Rename both the file and class name to MainViewModel.

Next we’re going to do a bit of a tidy up. By default the project that contains the XAML for the application (i.e. App.xaml) and for the main page of the application (MainPage.xaml) was given the same name as the solution itself. I’m not a big fan of that so I rename this to have the UI suffix. To do this you need to remove the existing project, rename the folder and project name, and add the existing project back into the solution. Don’t forget that you’ll need to update the namespace for both App and MainPage classes (in both XAML and code behind files) to include UI (e.g. the full type name of the MainPage class should be StrataPark.UI.MainPage)

After renaming the UI project, we need to double check that all the projects have the correct references. The only project reference the UI project should have is to the Core project

image

All three of the head projects (i.e. for iOS, Android and UWP) should reference both the Core and UI projects

image

Now’s another time to check that everything builds and runs (all three platforms) and then commit your changes!

Both the Core and UI projects are currently just .NET Standard 2.0 projects. This means that all code is the same for all platforms. By making these projects multi-targeted, we can enable platform specific code to be included where necessary. This is similar to the way shared libraries used to work. However, the difference is that the code stays in a separate assembly, away from the head projects.

To make use of multi-targeting, first create a file called global.json in solution folder, with the following contents:

{
     "msbuild-sdks": {
         "MSBuild.Sdk.Extras": "1.6.47"
     }
}

The MSBuild.Sdk.Extras package extends the raw multi-targeting support provided by Visual Studio/MSBuild. For both Core and UI projects, edit the csproj and replace the default TargetFramework element at the beginning of the file with the following (make sure you include the Project element as this sets the Sdk to use)

<Project Sdk="MSBuild.Sdk.Extras">
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0;Xamarin.iOS10;MonoAndroid81;uap10.0.16299</TargetFrameworks>
   </PropertyGroup>

  <ItemGroup>
     <Compile Remove="Platforms\**\*.cs" />
     <None Include="Platforms\**\*.cs" />
   </ItemGroup>
  
   <ItemGroup Condition=" $(TargetFramework.StartsWith('netstandard')) ">
     <Compile Include="Platforms\Netstandard\**\*.cs" />
   </ItemGroup>
  
   <ItemGroup Condition=" $(TargetFramework.StartsWith('uap')) ">
     <Compile Include="Platforms\Uap\**\*.cs" />
   </ItemGroup>

  <ItemGroup Condition=" $(TargetFramework.StartsWith('Xamarin.iOS')) ">
     <Compile Include="Platforms\Ios\**\*.cs" />
   </ItemGroup>

  <ItemGroup Condition=" $(TargetFramework.StartsWith('MonoAndroid')) ">
     <Compile Include="Platforms\Android\**\*.cs" />
   </ItemGroup>

If you take a look at the code that was added to the csproj, you can see that there are some conditional inclusions based on the target platform. We’ll make use of this to return a platform specific welcome text for our application.

Add a Platforms folder to the Core project

Add Netstandard, Ios, Android and Uap sub-folders to the Platforms folder

Add a file called MainViewModel.Platform.cs to each sub-folder of the Platforms folder with the following text. Replace Netstandard with the name of the platform (i.e. the sub-folder name)

public partial class MainViewModel
{
     private string PlatformWelcomeText => "Welcome from Netstandard";
}

Next, we’ll modify the MainViewModel.cs file. Note how the WelcomeText property returns the platform specific text

public partial class MainViewModel
{
    public string WelcomeText => PlatformWelcomeText;
}

In the MainPage.xaml, add a new Label element that is bound to the WelcomeText property

<Label Text="{Binding WelcomeText}" />

In the codebehind for the MainPage.xaml, add the following code to the end of the MainPage constructor

BindingContext = new MainViewModel();

Now when we build and run the application on each platform, we’ll see a platform specific welcome.

image

This technique can be used to include all sorts of platform specific code within your application, making it easier to deal with the Mvvm abstraction when you need to tie into platform specific APIs. In the past you’d have typically had to create a service in the head project, or some other clumsy workaround.

MVX=1F: TipCalc with Xamarin.Forms (MVX+1 days of MvvmCross)

In this post I’m going to extend the TipCalc to include Xamarin.Forms targets, similar to what we did in the post MVX=0F: A first MvvmCross Application (MVX+1 days of MvvmCross)

Adding Xamarin.Forms

Note: The following instructions can be applied to any project by simply replacing TipCalc with the name of your project

  1. Add a New Project based on the Mobile App (Xamarin.Forms) template 
    image

  2. In the New Cross Platform App dialog, select Blank App, check the Platforms you want, select .NET Standard and click OK
    image

  3. Upgrade the Xamarin.Forms NuGet to latest for all four Forms projects
  4. Add MvvmCross NuGet Package to all Forms projects (Forms, Forms.iOS, Forms.Android and Forms.UWP)
  5. Add MvvmCross.Forms NuGet Package to all Forms projects (Forms, Forms.iOS, Forms.Android and Forms.UWP)

Update the TipCalc.Forms project

  1. Remove all code in App class except for constructor with a call to InitializeComponent
  2. Create Views folder
  3. Move MainPage into Views folder and rename to FirstView
  4. Adjust FirstView.xaml and FirstView.xaml.cs to change class name to FirstView and to make it inherit from MvxContentPage

Update the FirstDemo.Forms.Uwp project

  1. Update Microsoft.NETCore.UniversalWindowsPlatform
  2. Add reference to TipCalc.Core
  3. Change MainPage to inherit from MvxFormsWindowsPage
  4. Remove all code other than the InitializeComponent method call in the constructor of MainPage
  5. Add ProxyMvxApplication
    public abstract class ProxyMvxApplication : MvxWindowsApplication<MvxFormsWindowsSetup<Core.App, TipCalc.Forms.App>, Core.App, TipCalc.Forms.App, MainPage>
  6. Change App.xaml and App.xaml.cs to inherit from ProxyMvxApplication
  7. Remove all code other than the constructor, with a single call to InitializeComponent, in App.xaml.cs

Update the FirstDemo.Forms.Android project

Note (1): If you run into the following error, you may need to rename your project. In this case we renamed it to Forms.Droid (as well as the folder the project resides in)
1>C:\Program Files (x86)\Microsoft Visual Studio\Preview\Enterprise\MSBuild\Xamarin\Android\Xamarin.Android.Common.targets(2088,3): error MSB4018: System.IO.PathTooLongException: The specified path, file name, or both are too long. The fully qualified file name must be less than 260 characters, and the directory name must be less than 248 characters.

Note (2): If you’re using the preview build of Visual Studio, you may run into an error: “error XA4210: You need to add a reference to Mono.Android.Export.dll when you use ExportAttribute or ExportFieldAttribute.” If you do, you just need to Add Reference to Mono.Android.Export (search in the Add Reference dialog).

  1. Change Forms.Android project to target latest Android SDK
  2. Upgrade Xamarin.Android.Support.* to latest for the Forms.Android project
  3. Add reference to TipCalc.Core
  4. Change MainActivity inheritance, remove code except for a constructor:
    public class MainActivity : MvxFormsAppCompatActivity<MvxFormsAndroidSetup<Core.App, App>, Core.App, App>
    {
    }

Update the TipCalc.Forms.iOS project

  1. Add reference to TipCalc.Core
  2. Changed inheritance of AppDelegate
    public partial class AppDelegate : MvxFormsApplicationDelegate<MvxFormsIosSetup<Core.App, TipCalc.Forms.App>, Core.App, TipCalc.Forms.App>


Adding TipCalc Xamarin.Forms Layout

Update the TipCalc.Forms project by updating the FirstView.xaml with the following XAML.

<?xml version="1.0" encoding="utf-8" ?>
<views:MvxContentPage
     xmlns:views="clr-namespace:MvvmCross.Forms.Views;assembly=MvvmCross.Forms"
     xmlns="
http://xamarin.com/schemas/2014/forms"
              xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
              x:Class="TipCalc.Forms.Views.FirstView">
  
  <StackLayout>
         <Label Text="SubTotal"/>
         <Editor Text="{Binding SubTotal, Mode=TwoWay}"/>
         <Label Text="How generous?"/>
         <Slider Value="{Binding Generosity, Mode=TwoWay}"
                     Minimum="0"
                     Maximum="100"/>
         <Label Text="Tip:"/>
         <Label Text="{Binding Tip}"/>
         <Label Text="SubTotal:"/>
         <Label Text="{Binding Total}"/>
     </StackLayout>

</views:MvxContentPage>

That’s it – there’s nothing more to do in order to add Xamarin.Forms targets (iOS, Android and UWP) to the TipCalc

MVX=0F Side Note: Adding a Splash Screen

I received some feedback on my previous post on setting up MvvmCross for Xamarin.Forms, asking how to add a splash screen to the Android Forms application. In the post MVX=0 I converted the MainActivity that comes as part of the standard Xamarin Android project into a SplashScreen but when it came to the Android project for Xamarin.Forms I left it without a splash screen.

Luckily adding a splash screen is really easy, so let’s add one to the Forms.Droid project:

  1. Copy the SplashScreen.axml from the /Resources/layout folder in the FirstDemo.Droid project into the /Resources/layout folder in the Forms.Droid project
  2. Remove “MainLauncher = true” from the Activity attribute on the MainActivity
  3. Change the MainActivity inheritance:
    public class MainActivity : MvxFormsAppCompatActivity<MainViewModel>
  4. Add a new class, SplashScreen.cs:
    [Activity(Label = "FirstDemo.Forms.Splash", Theme = "@style/MainTheme", MainLauncher = true, NoHistory = true)]
    public class SplashScreen : MvxFormsSplashScreenAppCompatActivity<MvxFormsAndroidSetup<Core.App, App>, Core.App, App>
    {
         public SplashScreen() : base(Resource.Layout.SplashScreen)
         {
         }
  5.     protected override void RunAppStart(Bundle bundle)
         {
             StartActivity(typeof(MainActivity));
             base.RunAppStart(bundle);
         }
    }

And there you have it – the Android Xamarin.Forms project will launch with a splash screen before redirecting to the MainActivity which will host the Xamarin.Forms content.

Declarative C# as an alternative to XAML

Yesterday I had one of those moment where one minute you’re super opinionated on something, only for someone to point out how things have changed and that you should re-evaluate your position – As much as I have my personal preferences on a lot of developer related topics, I try to listen to those around me and look at why they’re doing things their way, and whether I can adapt/learn/extend what I’m doing.

Yesterday in my post talking about CSS in Xamarin.Forms I made a comment that developers building for Xamarin.Forms should be using XAML and “if you’re doing it in code, you’re wasting everyone’s time”. Almost immediately after posting this I was following a related twitter thread (Adam’s thread on whether XAML is holding Xamarin.Forms back) and I saw a link to the work that Vincent has been doing on using declarative c# instead of XAML. This started with a discussion on the Xamarin forums: https://forums.xamarin.com/discussion/123771/using-declarative-style-c-instead-of-xaml-should-xamarin-redirect-xaml-efforts-elsewhere? Then Vincent provided a link to his repo on Github: https://github.com/VincentH-Net/CSharpForMarkup

My issue with using C# to define layout is that out of the box it’s very difficult to construct layouts without it making it look like a jumbled mess – XAML makes the layout very clean and easy for any XAML developer to easily grok what’s going on. However, what Vincent has done is provide some simple extensions that make it possible to define the layout in a very fluent manner.

Whilst I still prefer, and would recommend using XAML, if you must use C# to define layouts, you should look at the work Vincent has done and perhaps leverage it in your code. Furthermore I’d love to see some metrics on whether there is a noticeable performance gain in using C# versus compiled XAML, and how to handle styles, templates and other resources in code.

Xamarin Forms gets CSS to pander to web developers

I just finished reading a good post by fellow Microsoft MVP, Sam Basu, looking at how to use CSS for styling web development. Since becoming aware of the intent to add CSS as a styling option with Xamarin Forms I’ve been an advocate against it, not because I’m “not a web guy” but because the platform doesn’t need options. Xamarin Forms is a great platform and one that I’ve been talking, blogging and working with since it was created; it’s not perfect but it’s incredibly powerful in how quickly cross-platform applications can be generated. What it does not need is a second alternative for styling.

In talking with the product team and other Xamarin Forms developers I’m always keen to understand their opinions, so I decided that I’d review Sam’s list of CSS benefits and try to boil them down into why I think the decision was made to add CSS. My summary of the list it comes down to (I’ve discounted the other comments because they’re just statements, not really benefits of CSS over XAML styling):

- The developer ecosystem is inundated with web developers (ie people who know and understand CSS) so let’s give them a technology they’re familiar with (without having to learn anything new)

- CSS is less verbose

- CSS offers additional styling inheritance

-  CSS can be shared between web and Xamarin Forms applications

Let me leave the first point for a second – I promise I’ll come back to it. The second point regarding CSS being less verbose is a bit irrelevant since intellisense/autocomplete makes writing XAML styles super quick; XAML styles are then compiled and so don’t need to be parsed in the way CSS does. I have to admit, one of the only benefits I see of using CSS is around styling inheritance and referencing – this has always been a limitation of XAML styles and one that I would love to see a fix for, rather than cobbling some other styling alternative. The last point regarding sharing CSS between web and Forms might be nice in theory but as we’ve seen say across Phone, Windows, Xbox, the reality is that most of the styling needs to be adjusted per platform anyhow, so the benefits are marginal at best.

The article goes on to talk about some caveats – I’ll rephrase this as “Here are the reasons you should never use CSS in you Xamarin Forms application”:

- XAML styling is, and I’m guessing, will continue to be the primary way to do styling in Xamarin Forms – anything else will be built on top of this meaning that all new features will come later, if at all, to CSS

- There are some limitations on what CSS can do, even today – do you think this will get addressed any time soon? I wouldn’t be betting the future of any project on these getting addressed in the short term, if ever.

- CSS is parsed – Xamarin/Xamarin Forms adds enough overhead as it is, do you really want to slow down your mobile apps further. Just on this note, please make sure you optimise your apps, leveraging XAML compilation

Ok so I mentioned I’d come back to the first benefit of using CSS which is that it’s a familiar technology for web developers – the reality is that Xamarin.Forms is for building mobile applications and unless you’ve come from a background of building SPAs with offline capabilities (such as building a PWA), chances are you’re going to need to learn a bunch more than just XAML syntax. Furthermore, if you’re going to be building with Xamarin.Forms you need to be using XAML to layout your pages (if you’re doing it in code, you’re wasting everyone’s time), so why wouldn’t you use XAML styling too.

Now, do I think that XAML styling is perfect? – it is definitely not. The lack of even simple things like multiple inheritance, and in the case of Xamarin.Forms, basic control templates for the standard controls, are annoyances and need to be fixed. I think there is an opportunity to learn from CSS and adapt it to improve XAML across the board. Do I think this is a good enough reason for adding CSS? NO, I repeat NO – you can’t imagine the resource drain that CSS will have on the Xamarin.Forms product team (bugs, feature requests, support for new features).

Going forward I’d like Xamarin.Forms to focus on core requirements with a view to “bringing back the magic”.

PWA Follow Up

It’s clear that talking about Progressive Web Applications (PWAs) is all the rage. I noticed today that fellow Microsoft MVP, Adam Pedley who runs the Xamarin Help website and blog, posted about where PWAs and Xamarin.Forms fit. Whilst I’m not sure I agree with his opening statement about PWAs being started by Google (there is a long legacy of different browsers providing pseudo-offline features which pre-date the term PWA, so the concept itself isn’t new), I will definitely agree that it has been Google that has been championing the cause, with Microsoft adding some behind the curtain support (eg PWABuilder.com). One of the most interesting points that’s worth highlighting is the disconnect between the device features/capabilities that the web and client applications (native, Xamarin or Xamarin Forms) can take advantage of. Whilst the difference is being progressively eroded, there are still plenty of areas where a client application is the way to go. Shout out to https://whatwebcando.today/

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New BuildIt Release for NetStandard 2.0 (General, States and Forms)

A new release of the following libraries is available via NuGet (v1.1.0.134):

- BuildIt.General

- BuildIt.States

- BuildIt.Forms

Whilst not much has changed in terms of features, behind the scenes there was quite a significant change as we adjusted the solution/project structure, and thus the nuget package structure. We took advantage of the ability to multi-target which meant we no longer have to have separate projects/libraries in order to support platform specific features. BuildIt.General, which used to have a UWP specific library, is now a single libary. Same goes for BuildIt.States. BuildIt.Forms has two libraries, down from the 5 that it used to have.

Additionally we also added direct support for netstandard 2.0. As part of the build process, each library is compiled for netstandard 1.0, netstandard 2.0 and then any platforms that have additional features.

In this release we’ve released multiple packages with the same version number, even though there is an interdependency between them (Forms –> States –> General).

Please reach out and let me know if you see any issues in this release with any of these libraries. We’ll be working to release updates to the other BuildIt libraries over the coming weeks.