DotNetMaui (Xamarin.Forms) is Not a XAML Platform

Yeh I know I’m going to get a ton of abuse about how this title is just click bait but before you start with the comments, hear me out. Firstly, the title is actually just missing a word DotNetMaui is Not JUST a XAML Platform In this post we’ll go through why DotNetMaui/Xamarin.Forms is/is not … Continue reading “DotNetMaui (Xamarin.Forms) is Not a XAML Platform”

Yeh I know I’m going to get a ton of abuse about how this title is just click bait but before you start with the comments, hear me out. Firstly, the title is actually just missing a word

DotNetMaui is Not JUST a XAML Platform

In this post we’ll go through why DotNetMaui/Xamarin.Forms is/is not a XAML platform and discuss the inclusive approach that the team has taken that allows for the inclusive of approaches such as those proposed by Vincent (C# markup) and James (Comet).

I want to start off by saying that Xamarin.Forms is a great cross-platform technology for rapidly building apps that work across iOS, Android, Windows (UWP), MacOS etc. At Built to Roam we continue to deliver apps for customers using this technology. DotNetMaui will continue this trend and will no doubt be a great platform for developers to build apps that work across various operating systems and devices. This post is in no way supposed to be a criticism, rather an objective look at what DotNetMaui/Xamarin.Forms is and is not. This is 100% from my perspective and I respect that other developers are entitled to their opinions (feel free to leave a comment!)

XAML as Declarative Markup

Historically, there have been various technologies/frameworks that have used XAML as the markup language. Typically, we think of the UI frameworks such as Windows Presentation Foundation (WPF), Silverlight, Windows Phone, Windows (UWP) but XAML has been used as the markup language for other non-UI technologies, for example Windows Workflow Foundation. XAML is fundamentally about declarative markup and in the case of UI frameworks it was for describing layout.

For those developers who have built, or are even still building, using Windows Forms, you’ll remember the pain of trying to coerce the designer to behave. The designer was really just a glorified code generator but the frustration came because if you attempted to modify the generated code, when you reopened the designer it would undo or break your changes. With XAML, this shouldn’t happen because, assuming it’s well-formed, it adheres to the schema…. in theory anyhow.

At this point it’s worth pointing out that in some regards XAML is literally just a way of declaring the creation of a hierarchy of objects. In fact, I’ve often added instances of non-UI classes in XAML just so that they’re available as resources that I can reference from XAML or code throughout my application. If you continue down this line of reasoning, it’s no surprise that you can indeed create your UI in markup (a proposition being peddled heavily by Vincent with his contribution to C# markup for Xamarin.Forms).

XAML Databinding

When developers think about XAML, they often package that together with MVVM and/or data binding. This is not unreasonable since the data binding framework was one of the main selling points that Microsoft would talk about when promoting any XAML technology.

Xamarin.Forms does have great support for data binding. Whilst it doesn’t support the x:Bind syntax introduced in Windows (UWP) which uses code generation to make data binding strongly typed, it does support compiled bindings making XAML quite an efficient technique for defining layout and data binding.

Here’s the question though – if the compiler is just going to convert XAML into compiled code, why don’t we just write it in C# and remove the need to learn the XAML abstraction? (i.e. back to Vincent’s point about C# markup!)

Model-View-Update (MVU)

Over the last couple of years there have been a number of new frameworks and technologies that have provided alternative strategies for updating the UI. Web frameworks such as React use a virtual DOM to deliver rendering efficiencies. More recently we’ve seen Flutter take the learnings from building the rendering engine behind Chrome and applying it as an application framework. This has lead to a lot of excitement about MVU (for the moment I’m going to ignore the argument that Flutter, SwiftUI and Comet/DotNetMaui are not MVU as proposed by the Elm architecture).

There have been several spikes on implementing MVU style frameworks for both Xamarin.Forms and Windows/UWP. All of them that I’ve seen focus on replacing XAML with C# code that declares the layout, with some smarts that only push differences to the UI rendering engine.

As Xamarin.Forms evolves to DotNetMaui we’re going to see some changes to the rendering framework. As the work by James Clancey on Comet is integrated there will be changes to the use of platform renderers. Microsoft is taking a gamble that as they make the necessary changes to Xamarin.Forms/Xamarin.iOS/Xamarin.Android/UWP to align with the .NET roadmap, they’ll take this opportunity to address some of the limitations/frustrations felt by developers with the current rendering engine.

Rendering Engine

There is no proposal to fundamentally change the way that Xamarin.Forms/DotNetMaui uses the native platform controls. The premise is that apps should use the controls that have been provided by the platform. This should encourage developers to build apps that belong on each platform. This thinking is dated, and most customers don’t care about platforms details, they just want their apps to look consistent on every platform.

This lead the team to add the Visual attribute and subsequently the Material Visual. If you’re looking to build a great looking app out of the gate, using the Material Visual is the way to go. However, you do have to ask yourself why did they need to introduce the concept of a Visual when we have styles? and can’t we just change the template of controls to change how they look?

Lookless Controls make a XAML Platform

I’ve conceded early in this post that a XAML platform is really any technology that uses XAML as a markup; thus DotNetMaui/Xamarin.Forms is indeed a XAML platform. However, when we consider what we mean by a XAML platform we typically associate it with a number of capabilities (in no particular order, and I’m sure there are other things that I’ve left off the list):

  • Styles and Resources
  • Data binding
  • Data Templates
  • Visual States
  • Control Templates

Further more I would go so far to say that one of the core principles of a XAML platform is that of Lookless Controls (this term seems to have been lost to history somewhat but was heavily used in the context of WPF and the way controls were templated). This is the ability to completely re-template a control without losing the basic functionality. This is something that has never been adopted by Xamarin.Forms and isn’t likely to emerge in DotNetMaui. In order for a platform to support the concept of Lookless Controls, each control needs to have a ControlTemplate that can be used to define both the static look and feel of the control but also the various Visual States (and transitions) of the control.

Developers considering different cross platform technologies might ask what the difference is between the DotNetMaui/Xamarin.Forms approach and that taken by the Uno Platform. Without listing all the differences, one of the core differences is the support for Lookless Controls and control templating. As ControlTemplates and Visual States are fundamental to the delivery of Lookless Controls on the Windows (UWP/WinUI) platform, they are a core part of the way that the Uno Platform renders apps on each platform.

Not JUST a XAML Platform

The last section seems like I’m being overly negative on the DotNetMaui/Xamarin.Forms platform and I must admit for the longest time I was frustrated that the team hadn’t prioritised making it easier for developers to re-template controls. Whilst I still prefer a platform where I’m in control and can change the template of controls as needed, I recognise that in the majority of cases, this isn’t required in order to deliver great looking apps.

If we look at what’s in scope for DotNetMaui we see that there inclusive approach will provide developers with many options to develop and style their application. This will make DotNetMaui a great starting point for developers wanting to build apps using the Microsoft tool chain, and of course provide a great feeder into building apps that connect and work well with Azure.

Picking Your Platform

At this point you might be asking yourself how do you decide which platform to pick for building your next cross platform application. This is a question that I ask daily and the answer is that it really depends on the situation, the customer, the development team etc. So for a minute, lets limit the scope to the Microsoft ecosystem and consider the following three options:

  • Power Apps – I haven’t talked about these in this post but if you’re looking for a minimal code platform that connects to Microsoft 365 and the Power platform, then this is your best option. It’s not really a true cross platform app platform but worth considering as it’s massively powerful for working with enterprise data and workflows
  • DotNetMaui/Xamarin.Forms – If you’re looking to rapidly deliver great looking apps where the designs are derived from the Material design language without wanting to curate animations, effects and styles, then DotNetMaui/Xamarin.Forms is the way to go. Pick the approach (eg MVVM or MVU) and language (eg C# or XAML) that suits your team.
  • Uno Platform/WinUI – If you’re looking for granular control over every aspect of your application then you can’t go past the Uno Platform. This platform is evolving at an amazing pace providing support for Web Assembly, Skia backend and much more. Each control has a ControlTemplate that you can override and customise precisely the way you want it.

Windows (UWP) Designer in Visual Studio and Blend for Visual Studio

If you’ve been looking at the release notes for the Visual Studio previews, you’ll have noted that there’s some work being done on the XAML designer that now supports both WPF and UWP. I figured I would take this opportunity to go through and document some of the features that I use and some of … Continue reading “Windows (UWP) Designer in Visual Studio and Blend for Visual Studio”

If you’ve been looking at the release notes for the Visual Studio previews, you’ll have noted that there’s some work being done on the XAML designer that now supports both WPF and UWP. I figured I would take this opportunity to go through and document some of the features that I use and some of the new features that have appeared in the previews. Note that this isn’t an exhaustive list by any means – would love feedback on what other features you use and what you think is missing in the designer.

One of the reasons that the designer experience in Visual Studio and Blend is so relevant is that you can take the design you’ve done for your Windows app and port it across to iOS, Android, MacOS and even the web (using Web Assembly). All these platforms are available via the Uno platform – If you’re new to the Uno Platform, head over to and get started with building cross-platform mobile, desktop and Web applications.

New Project

Ok, so let’s start by creating ourselves a new Windows (UWP) project based on the Blank App (Universal Windows) template.

As usual, give the project a name to get started – you’ll be prompted to pick which target and minimum versions of Windows you want but for the purpose of this post I just went with the defaults.

Visual Studio Designer

Once created, depending on your setup of Visual Studio, you’ll probably have the MainPage.xaml already open. If not, find MainPage.xaml in the Solution Explorer tool window and double-click it to open it. Here you can see that I have the Toolbox on the left of the design surface and the Properties window, above the Solution Explorer, on the right side. I find this layout works well for working with the designer but you can easily customise the layout of the tool windows to suit how you work.

Design in Blend

We’re actually going to switch across to Blend for Visual Studio for the rest of this post. I prefer to do any designer work in Blend because I prefer to have the tool windows in a different position when doing design work, than when writing code. Switching between Visual Studio and Blend also gives me a mental switch to go between designer mode (well at least “layout-oriented work” mode, since I’m clearly not a designer) and developer mode.

It’s worth noting that the designer experience in Visual Studio and Blend is very similar – Microsoft made the decision years ago to build a consistent experience with the majority of functionality now available in both tools. Blend still retains a number of designer oriented features, such as creating visual states and animations with storyboards, that haven’t been exposed in the Visual Studio designer.

You can easily switch to Blend by right-clicking on the project or a XAML file in Solution Explorer and selecting Design in Blend.

As you can see the tool windows are labeled slightly differently in Blend and have a different default position. Again, feel free to reposition them to suit how you work.


If you look at the main design surface, you’ll note that the initial position of the MainPage is very small. Working at this zoom level will be quite hard as each of the elements will be small and hard to manipulate.

In the bottom left corner of the design surface there’s a series of icon buttons and a dropdown. Expanding the dropdown allows you to select from a number of predefined zoom levels.

Alternatively you can select Fit all, or Fit selection, in order to bring the whole page into view.

The other way that you can control the positioning of the design area is using the mouse:

  • Scroll up/down – Two-finger drag on touch pad, or scroll wheel on mouse
  • Scroll left/right – Hold Shift + Two-finger drag on touch pad, or scroll wheel on mouse
  • Zoom in/out – Hold Ctrl + Two-finger drag on touch pad, or scroll wheel on mouse

Adding Controls with Assets Tool Window

Let’s start to add some controls to the page. We’ll use the Assets tool window to locate the TextBlock control using the search function.

If I just click and drag the TextBlock onto the design surface, Blend will add the control where I drop it.

Objects and Timeline Tool Window

If we take a look at the XAML you’ll note that a very arbitrary margin has been set on the TextBlock

Layout – Reset All

Right-click on the TextBlock in the Objects and Timelines tool window and select Reset All from the Layout menu.

Now the TextBlock has been reposition to take up the whole page.

However because text flows from the top-left, the word TextBlock is in the top left corner of the page.

Edit Style – Apply Resource

Next, let’s increase the size of the text. Instead of manually setting FontSize, we’re going to make use of one of the existing TextBlock styles. Right-click on the TextBlock again in the Objects and Timeline window and select Edit Style, Apply Resource and then we’ll select HeaderTextBockStyle. You can read more about predefined styles and the use of typography here.

This gives our TextBlock a nice size, without hard coding font sizes and styles randomly throughout the application.

Design Surface

Up to now I haven’t given you much context for this app – we’re going to build a simple interface that shows a list of contacts. The TextBlock we’ve added so far will act as a header/title for the page, and then beneath it we’ll need a ListView showing the list of our contacts.

Drawing Grid Rows

Before we can add the ListView, let’s create two rows in the Grid that the TextBlock is sitting in. Select the Grid in the Objects and Timelines window and then on the design surface, if you move the mouse cursor near the edge of the page, you’ll see the cursor change to one that’s got a small plus sign on it. Clicking at this position will add a row to the Grid.

Once added, you can then adjust the sizing of the row. In this scenario we’re going to change the row from 33* to being Auto, which will mean the row will be sized based on the height of the TextBlock.

Reset Grid.RowSpan in Properties Tool Window

One thing you may notice is that after adjusting the row size, the row seems to disappear. This is because in creating the row, Blend decided that the TextBlock was going to span both rows. To fix this, we can change the RowSpan on the TextBlock from 2 to 1 using the Properties tool window.

In this case, we’re going to select the Reset option, rather than setting it explicitly to 1. This will mean one fewer attributes in XAML that needs to be parsed.

Assets Button

Next up, we’re going to add the ListView to the second row. This time, instead of going all the way to the Assets tool window, we’re going to use the dropdown from the chevrons on the top left of the designer. This allows us to easily search and add controls, without having to open the tool windows – when doing a lot of design work I will often hide the tool windows (or even detach them and put them on a different monitor), so not having to open the tool windows to find a control is quite handy.

Runtime Toolbar

After dragging the ListView onto the page and making sure it’s sitting in the second row, I’m going to run the application to see what it looks like. Note that despite me not doing anything, the color of the title bar has aligned with my Windows theme (and yes, it’s pink because I’m using the setting where the theme is derived off the background I have set, which in turn is changed daily using the Dynamic Theme app).

Hot Reload

You’ll also note at the top of the window there is a toolbar that’s been added whilst I’m debugging the application. This toolbar has been available for a while but the Hot Reload indicator is a new addition. Hot Reload allows you to make changes to your XAML and for it to immediately take effect on the page when you save the XAML file (Hot Reload can be configured via Options off the Tools menu).

Display Layout Adorners

I’m going to toggle the Display Layout Adorners button (immediately adjacent to the left of the Hot Reload green tick).

Select Element

Next I’m going to click on the Select Element button (second in from the left) and click on the open space immediately below the TextBlock. As you can see, this highlights the whole area in a light blue (the layout adorner) which is the ListView.

Go to Live Visual Tree

Next I can click on the Go to Live Visual Tree button (first from the left) which will switch back to Visual Studio with the focus being set on the appropriate node in the Live Visual Tree.

XAML Editor

You’ll also note that the corresponding code in the XAML editor has been selected. As I start to type in the XAML editor I get intellisense showing me what options I have.

I’ve gone ahead and set a simple data template for the ListView which will determine what’s displayed for each item in the list. In this case it’s just going to print the word “Hi” for each item.

XAML Highlighting

Note that as I move the cursor around the XAML editor, the matching pairs of XML tags are highlighted, making it easy to see start and end of the blocks of XAML.

DataContext for Data Binding

Currently, despite setting a data template, the ListView isn’t going to show any items because I haven’t connected it to any data. To allow me to continue to layout elements on the page I’ve created some mock, or fake, data.

public class FakeData
    public Contact[] Contacts { get; } = new[]
        new Contact(){Name="Bob Jones",PhoneNumber="+1 442 002 3234", Photo="ms-appx:///Assets/Photos/p0.jpg"},
        new Contact(){Name="Jessica Phelps",PhoneNumber="+1 394 234 1235", Photo="ms-appx:///Assets/Photos/p1.jpg"},
        new Contact(){Name="Andrew Jenkins",PhoneNumber="+1 232 282 29321", Photo="ms-appx:///Assets/Photos/p2.jpg"},
        new Contact(){Name="Francis Davis",PhoneNumber="+1 92329 2923 923", Photo="ms-appx:///Assets/Photos/p3.jpg"},
        new Contact(){Name="Xavier Smith",PhoneNumber="+1 93483 3923423", Photo="ms-appx:///Assets/Photos/p4.jpg"},
        new Contact(){Name="Kevin Chow",PhoneNumber="+1 343 994 39342", Photo="ms-appx:///Assets/Photos/p5.jpg"},
        new Contact(){Name="Phil Stevenson",PhoneNumber="+1 885 367 44432", Photo="ms-appx:///Assets/Photos/p6.jpg"},
        new Contact(){Name="Heath Sales",PhoneNumber="+1 903 912 9392", Photo="ms-appx:///Assets/Photos/p7.jpg"},
        new Contact(){Name="Sarah Wright",PhoneNumber="+1 347 399 499234", Photo="ms-appx:///Assets/Photos/p8.jpg"},
        new Contact(){Name="Geoff Sans",PhoneNumber="+1 834 1232 01923", Photo="ms-appx:///Assets/Photos/p9.jpg"}

I can go ahead and create an instance of the FakeData class as a Resource on the Page. This instance is then set as the DataContext for the root Grid element on the page (and subsequently the DataContext for all elements on the page).

The ItemsSource on the ListView is then data bound to the Contacts property on the FakeData instance. The running application updates immediately to show a list of “Hi” down the screen.

Hide the Runtime Toolbar

As we start to design the page, the toolbar at the top can often get in the way. If you click on the chevron on the right side of the toolbar, the first click will reduce the size of the Hot Reload indicator (removing the words Hot Reload). The second click will minimise the toolbar completely.

Let’s amend the data template for the list, this time data binding to the Name property.

The ListView is immediately looking better, showing the names of the people in the Contacts list.

Edit ListView Item Template

If your working in the designer there are a number of ways you can make changes to the data template for the list. In this example we’re using the dropdown at the top left corner of the design area. Clicking the down button, followed by Edit Additional Template, then Edit Current, then Edit Generated Items (ItemTemplate).

Objects and Timeline – Group Into

You’ll notice that the Objects and Timeline window updates to show the tree from the perspective of the data template. Right-clicking on the TextBlock I can select Group Into, followed by StackPanel, to wrap the TextBlock in a StackPanel.

TextBlock Button

Next, I can add a TextBlock to the newly created StackPanel but simply double-clicking the TextBlock button on the left of the design area.

XAML Suggested Actions

One of the newest additions to the designer is the XAML Suggested Actions. Anyone who’s worked in Word or Excel is familiar with the suggested actions toolbar that often appears to try to make more of the tools are accessible when you need them. in this case we can click on the lightbulb button to display an in-situ property editor.

In this case we’re going to click through to Create Data Binding.

Create Data Binding

From the Create Data Binding window we can traverse down to the PhoneNumber property on the Contact object.

Note that there’s a minor bug at this point because the data binding that’s created isn’t 100% accurate. Instead of data binding to the PhoneNumber property (eg {Binding PhontNumber}) the generated binding is with Contacts.PhoneNumber. Simply removing the “Contacts.” prefix is enough to get it to work.

Edit ColumnDefinitions

I’m going to follow a similar approach to before – select the StackPanel and group into a Grid. From the Properties tool window find the ColumnDefinitions.

Click the … to open the Collection Editor for the ColumnDefinitions. Here we’re going to limit the first column to 50 pixels and then leave the second column as *.

I’ve update the data template with the profile picture as an image. Simply add an Image control and follow the same process as before to setup data binding to the Photo property on the Contact.

WinUI – ProfilePicture Control

To improve the layout of the contacts I’m going to use the ProfilePicture control, which will ensure all the images are the same size.. Instead of using the built in control, I’m going to grab the ProfilePicture control from the WinUI toolkit. Using the nuget package manager, select the Microsoft.UI.Xaml package and install it.

Once you’ve added the nuget package, make sure you don’t ignore the readme file that’s displayed to remind you to include the appropriate runtime values.

We’re almost there, we just need to add the PersonProfile, which we can do by discovering it in the Assets window (even though its from a third party)

And so now we have all our contacts appearing.

Final Design

After applying some minor tweaks to the layout of the data set, we can have a nicer looking sample app.

Before I copied the final code to this post, I just wanted to format the XAML. From the Options window, you can configure how you want your XAML files to appear.

Then, once you have the formatting options the way you want them, you can invoke Format Document from the various places around the design surface.

Final XAML

And here’s the final source code

<Page xmlns=""
        <local:FakeData x:Key="DesignTimeData" />

        <ThemeResource ResourceKey="ApplicationPageBackgroundThemeBrush" />

    <Grid DataContext="{StaticResource DesignTimeData}">
            <RowDefinition Height="Auto" />
            <RowDefinition />
        <TextBlock Margin="16"
                   Style="{StaticResource HeaderTextBlockStyle}" />
        <ListView Grid.Row="1"
                  ItemsSource="{Binding Contacts}">
                    <Grid Margin="8">
                            <ColumnDefinition Width="50" />
                            <ColumnDefinition />
                        <StackPanel Orientation="Vertical"
                            <TextBlock Text="{Binding Name}"
                                       Style="{StaticResource BaseTextBlockStyle}" />
                            <TextBlock Text="{Binding PhoneNumber}"
                                       Style="{StaticResource BodyTextBlockStyle}" />
                        <Custom:PersonPicture Width="50"
                                              ProfilePicture="{Binding Photo}" />

And that’s it – hopefully you’ve learnt a bit more about how to use the XAML editor and the new designer features.

iOS Hot Restart, Multi-Targeting and Solution Template for Cross-Platform Applications with Uno

In my last couple of posts I covered setting up multi-targeting and improving the developer experience with multi-targeting. This was in the context of an application that supported iOS (Xamarin iOS), Android (Xamarin Android) and Windows (UWP). In this post we’re going to look at a template for Uno cross-platform applications. If you’re new to … Continue reading “iOS Hot Restart, Multi-Targeting and Solution Template for Cross-Platform Applications with Uno”

In my last couple of posts I covered setting up multi-targeting and improving the developer experience with multi-targeting. This was in the context of an application that supported iOS (Xamarin iOS), Android (Xamarin Android) and Windows (UWP). In this post we’re going to look at a template for Uno cross-platform applications.

If you’re new to the Uno Platform, head over to and get started with building cross-platform mobile, desktop and Web applications.

The main points we’ll review are:

  • Creating a Uno application that targets iOS, Android, MacOS, Windows and Wasm (browsers/web).
  • Add class library, Core, for housing business logic (eg ViewModels)
  • Add class library, UI, for housing pages, controls etc
  • Add Hot Restart to the iOS head project
  • Add target framework switching and solution filters.
  • Refactoring project files to extract Uno references to make it easier to update references

If you want to jump straight to the final project/solution structure, then you can take a look at the final source code on the GitHub repository

Creating Your First Uno Application

For the purposes of this post we’re going to work with a new Uno application. However, there’s no reason why you can’t retrofit any, or all, of these steps to an existing project.

Start by searching for the Uno application template (If you don’t have these templates, then install them from the marketplace).

Give the application a name – We’ll use MultiTargetingWithUno.

Creating Uno Class Libaries

In this example, we’re going to create separate class libraries to house our pages and our ViewModels. But before we get on with creating them, we’re going to do a quick bit of tidying up.

Create PlatformHeads Solution Folder, and move all existing projects into PlatformHeads folder. This will group the head projects (i.e. the application projects that you can deploy and run) so that they don’t have other projects intermingled with them.

The next thing to do is to create two libraries: Core and UI. Search for Uno again but this time pick the Cross Platform Library option.

Next, give your library a name, and then repeat the process for both MultiTargetingWithUno.Core and MultiTargetingWithUno.UI libraries.

Delete the default Class1.cs file from both Core and UI projects, and make sure there is a reference from the UI project to Core.

Add reference to both UI and Core projects to the Shared project (so it gets added to each head project).

<?xml version="1.0" encoding="utf-8"?>
<Project xmlns="">
    . . .
    <ProjectReference Include="..\..\MultiTargetingWithUno.Core\MultiTargetingWithUno.Core.csproj" />
    <ProjectReference Include="..\..\MultiTargetingWithUno.Core\MultiTargetingWithUno.UI.csproj" />


This step is primarily around refactoring the Core and UI projects to make them easier to maintain by relocating various properties so that both projects share the same declarations.

In both Core and UI project files, the sdk references is MSBuild.Sdk.Extras/2.0.54. Change this by removing the specific version number, i.e. 2.0.54. Instead of specifying the version of the package inline, we’re going to specify it in a global.json file located in the solution folder.

Inside the globa.json we just need to include the sdk and its corresponding version number.

    "msbuild-sdks": {
        "MSBuild.Sdk.Extras": "2.0.54"

Your solution structure should look similar to the following.

Next we’re going to add a new solution item, libraries.targets. This is going to contain most of the properties that are in common across the Core and UI projects. This way if we need to adjust properties, we can do it in one place and have it applied to both libraries.

		<!-- Ensures the .xr.xml files are generated in a proper layout folder -->
	<PropertyGroup Condition="'$(TargetFramework)'=='netstandard2.0'">
	<ItemGroup Condition="'$(TargetFramework)'=='xamarinios10' or '$(TargetFramework)'=='MonoAndroid90' or '$(TargetFramework)'=='monoandroid10.0' or '$(TargetFramework)'=='netstandard2.0'">
		<PackageReference Include="Uno.UI" Version="2.4.0" />
		<Page Include="**\*.xaml" Exclude="bin\**\*.xaml;obj\**\*.xaml" />
		<Compile Update="**\*.xaml.cs">
		<UpToDateCheckInput Include="**\*.xaml" Exclude="bin\**\*.xaml;obj\**\*.xaml" />

Update the Core csproj file to remove everything inside the Project element, except the Import that references the newly created libraries.targets file.

<?xml version="1.0" encoding="utf-8"?>
<Project Sdk="MSBuild.Sdk.Extras">
	<Import Project="..\libraries.targets" />

Repeat this for the UI csproj file. However, you need to keep the project reference to the Core project.

<?xml version="1.0" encoding="utf-8"?>
<Project Sdk="MSBuild.Sdk.Extras">
	<Import Project="..\libraries.targets" />
		<ProjectReference Include="..\MultiTargetingWithUno.Core\MultiTargetingWithUno.Core.csproj" />

Target Framework Switching and Solution Filtering

As we did in my previous post, we’re going to update the Core and UI projects to allow for easy switching between active target framewrks.

We first need to add to the solution folder. This is used to setup various project properties that can be used to conditionally set what target frameworks are defined.

		<IsLibraryProject>!$(IsWasmHeadProject) and !$(IsAndroidHeadProject) and !$(IsiOSHeadProject) and !$(IsMacOSHeadProject) and !$(IsWindowsHeadProject)</IsLibraryProject>



	<PropertyGroup Condition=" '$(Configuration)' == 'Debug' ">

	<PropertyGroup Condition=" '$(Configuration)' != 'Debug' ">

Next, update the libraries.targets. The main changes are in bold, where the TargetsToBuild property is used to determine what target frameworks are defined.

	<PropertyGroup Condition=" '$(TargetsToBuild)' == 'All' ">
		<TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">uap10.0.16299;$(TargetFrameworks)</TargetFrameworks>

	<PropertyGroup Condition=" '$(TargetsToBuild)' != 'All' ">
		<TargetFrameworks Condition=" '$(TargetsToBuild)' == 'Android' ">monoandroid10.0;</TargetFrameworks>
		<TargetFrameworks Condition=" '$(TargetsToBuild)' == 'Windows' ">uap10.0.16299</TargetFrameworks>
		<TargetFrameworks Condition=" '$(TargetsToBuild)' == 'iOS' ">xamarinios10</TargetFrameworks>
		<TargetFrameworks Condition=" '$(TargetsToBuild)' == 'Mac' ">xamarinmac20</TargetFrameworks>
		<TargetFrameworks Condition=" '$(TargetsToBuild)' == 'Wasm' ">netstandard2.0</TargetFrameworks>

		<Compile Remove="**\*.netstandard.cs" Condition="'$(IsWASM)' != 'true'"/>
		<Compile Remove="**\*.droid.cs" Condition="'$(IsAndroid)' != 'true'"/>
		<Compile Remove="**\*.mac.cs" Condition="'$(IsMac)' != 'true'" />
		<Compile Remove="**\*.ios.cs" Condition="'$(IsiOS)' != 'true'"/>
		<Compile Remove="**\*.windows.cs" Condition="'$(IsWindows)' != 'true'" />
	<PropertyGroup Condition="'$(TargetFramework)'=='netstandard2.0'">
	<ItemGroup Condition="'$(TargetFramework)'=='xamarinios10' or '$(TargetFramework)'=='MonoAndroid90' or '$(TargetFramework)'=='monoandroid10.0' or '$(TargetFramework)'=='netstandard2.0'">
		<PackageReference Include="Uno.UI" Version="2.4.0" />
		<Page Include="**\*.xaml" Exclude="bin\**\*.xaml;obj\**\*.xaml" />
		<Compile Update="**\*.xaml.cs">
		<UpToDateCheckInput Include="**\*.xaml" Exclude="bin\**\*.xaml;obj\**\*.xaml" />

So that we can see what target framework was built, we’ll add the AppProperties.cs and each platform file (eg that we created in the previous post.

In order to switch target frameworks, add the launch batch files and solution filters – see previous post.

MainPage and MainViewModel

Ok, so now we can get on to adding some functionality. We’ll start by creating a ViewModels folder in Core project and then adding a basic class, MainViewModel.

namespace MultiTargetingWithUno.Core.ViewModels
    public class MainViewModel
        public string WelcomeText { get; } = "Hello World!";

The MainPage already exists, but it’s currently in the Shared project. Move the MainPage to UI project. After moving the MainPage, make sure you double check the csproj file for the UI project – Visual Studio has a nasty habit of adding unnecessary elements to the csproj. In this case, you shouldn’t have any explicit entries for MainPage.xaml or MainPage.xml.cs, since they will both be added to the project by default with the correct build action.

Update MainPage to correct the namespace from MultiTargetingWithUno.MainPage to MultiTargetingWithUno.UI.MainPage. We’ll also update the Text attribute on the TextBlock to use x:Bind to show the welcome message from WelcomeText property on the the ViewModel that’s created in the code behind.

    <StackPanel Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <TextBlock Text="{x:Bind ViewModel.WelcomeText}" Margin="20" FontSize="30" />

And the code behind which instantiates the MainViewModel.

using MultiTargetingWithUno.Core.ViewModels;

namespace MultiTargetingWithUno.UI
    public sealed partial class MainPage 
        public MainViewModel ViewModel { get; } = new MainViewModel();

        public MainPage()

Update App.xaml.cs in the Shared project to reference the MainPage (you may need to rebuild the solution in order for the intellisense to kick in and help you add the necessary using statements)

Set Windows head project (ie MultiTargetingWithUno.UWP) as the startup project and attempt to build and run the application.

If you see a message in Output window such as “Project not selected to build for this solution configuration”, change the Solution Platform to either x86 or x64 (alternatively you can modify the configuration to include the UWP head project when AnyCPU is selected).

Sometimes building for the first time you may need to force a rebuild of Core, UI and then the UWP head project.

At the time of writing, if you’d followed the steps to this point you’ll actually get an error similar to “error CS0103: The name ‘InitializeComponent’ does not exist in the current context”.

This is because the Uno.UI package hasn’t been added to the Mac target framework. To fix this, change the Condition for ItemGroup in the UI csproj from “‘$(TargetFramework)’==’xamarinios10’ or ‘$(TargetFramework)’==’MonoAndroid90’ or ‘$(TargetFramework)’==’monoandroid10.0’ or ‘$(TargetFramework)’==’netstandard2.0′” to just “‘$(TargetFramework)’!=’uap10.0.16299′” eg.

<ItemGroup Condition="'$(TargetFramework)'!='uap10.0.16299'">
	<PackageReference Include="Uno.UI" Version="2.4.0" />

And then, just when you thought we’d be done, you’ll also see another error, this time when you launch the UWP application:

System.AccessViolationException (0x80004003). Attempted to read or write protected memory. This is often an indication that other memory is corrupt.

This is a nasty error introduced by Microsoft at some point, preventing UWP applications from launching if there’s no pages defined in the application project. The solution is to add a dummy page to the UWP head project, call it “DoNotRemoveOrUsePage.xaml”.

Now you should be able to build and run the application but as you can see, there’s no indication of what platform we’re running on.

Let’s just update the WelcomeText on the MainViewModel to return platform information

public string WelcomeText { get; } = "Hello World! " + AppProperties.AppName;

That’s looking better – at this point you should be able to run the other platforms and see the welcome text vary with each platform.

Project File Refactor

In this section we’re going to do a bit of a tidy up of the Uno package references, extracting them out of the various project files so that they’re easier to manage in a central location.

Firstly we’ll add the logging packages to, since they’ll be used by the Core, UI and all the head projects.

	<PackageReference Include="Microsoft.Extensions.Logging.Console" Version="1.1.1" />
	<PackageReference Include="Microsoft.Extensions.Logging.Filter" Version="1.1.1" />

Next, we’ll create a new file, uno.targets, in the solution folder. This will include the Uno.Core (which all projects will refernece), along with Imports for different platforms. This will seem quite messy, and to be honest it is, but the way this is structured is based on a limitation of the legacy project system used by UWP, iOS, Android and Mac. The legacy project system won’t process conditional ItemGroups. However, they do support conditional Import statements, such as those in the uno.targets.

     <PackageReference Include="Uno.Core" Version="2.0.0" />

  <Import Project="uno.ui.targets"  Condition="'$(IsWindows)' != 'true' and '$(IsWindowsHeadProject)' != 'true'"/> 

  <Import Project=""  Condition="'$(IsAndroidHeadProject)' == 'true'"/>
  <Import Project="uno.wasm.targets"  Condition="'$(IsWasmHeadProject)' == 'true'"/>

  <Import Project="uno.debugging.targets"  Condition="'$(Configuration)' == 'Debug'"/> 

The uno.targets is imported into the so that it gets added to each project in the solution.

<Import Project="uno.targets" />

Create the uno.ui.targets file which includes a reference to the Uno.UI package. As you can see from the uno.targets file, the Uno.UI package needs to be imported into every project other than the Windows or Windows head projects

		<PackageReference Include="Uno.UI" Version="2.4.4"  />

Next up is the, which is used to add the Uno.UniversalimageLoader package to the Android head project.

		<PackageReference Include="Uno.UniversalImageLoader" Version="1.9.32" />

Then, the uno.wasm.targets includes the Bootstrap packages which are required by the Wasm head project:

		<PackageReference Include="Uno.Wasm.Bootstrap" Version="1.2.0" />
		<PackageReference Include="Uno.Wasm.Bootstrap.DevServer" Version="1.2.0" />

Lastly the uno.debugging.targets is only included for the Debug configuration.

		<PackageReference Include="Uno.UI.RemoteControl" Version="2.4.4"  />

With the uno.targets (and its nested imports) added to the, we can go through an clean up any references to Uno packages throughout the various project files.

  • In libraries.targets, remove ItemGroup with Condition “‘$(TargetFramework)’!=’uap10.0.16299′” that includes a package reference for Uno.UI
  • Remove references to Uno from head projects: Uno.UI, Uno.UI.RemoteControl, Uno.UniversalImageLoader, Uno.Wasm.Bootstrap, Uno.Wasm.Bootstrap.DevServer, Microsoft.Extensions.Logging.Console and Microsoft.Extensions.Logging.Filter

The other piece of refactoring we’ll do is to add a file to the solution folder, which defines various helpful properties and constants. These are useful if you ever have to write conditional logic in your code, or tweak debug output etc.

	<PropertyGroup Condition=" '$(Configuration)' == 'Debug' ">
	<PropertyGroup Condition="$(IsWASM)">
	<PropertyGroup Condition="$(IsWindows)">
	<PropertyGroup Condition="$(IsiOS)">
	<PropertyGroup Condition="$(IsMac)">
	<PropertyGroup Condition="$(IsAndroid)">

iOS Hot Restart

The last feature we’re going to add is support for iOS Hot Restart – the ability to run on an iOS device without needing a Mac! The Uno team blogged about this already but I’ll repeat it here to make things easier.

Add the following to main.cs – this will only be included in a debug build, so you don’t need to worry about it polluting your production code. Hot Restart works by pushing out a pre-built Xamarin.Forms application to the iOS device and then dynamically loading your application into it. This Uno doesn’t use Xamarin.Forms, this extra code is required to piggy-back on the process Microsoft has created for Hot Restart.

	public class HotRestartDelegate : Xamarin.Forms.Platform.iOS.FormsApplicationDelegate
		public override bool FinishedLaunching(UIApplication uiApplication, NSDictionary launchOptions)
			Windows.UI.Xaml.Application.Start(_ => new App());
			return base.FinishedLaunching(uiApplication, launchOptions);

Create uno.debugging.hotrestart.targets that references the Xamarin.Forms package.

		<PackageReference Include="Xamarin.Forms" Version="" />

Update uno.debugging.targets to conditionally import the uno.debugging.hotrestart.targets for the iOS head project.

<Import Project="uno.debugging.hotrestart.targets" Condition=" '$(IsiOSHeadProject)' == 'true' " />

Launch, Build and Run

There, we’re done and ready to run out application. If you load the MultiTargetingwithUno solution file, you should see all five head projects, along with the shared project, and then two class libraries. In this mode you can pick any head project as the start up project and run that application. However, it will be slow as it will have to build every target framework for the Core and UI libraries.


If instead, you double-click the Launch.iOS.bat, it will restrict the target framework to just iOS and then launch the ios solution filter. The Solution Explorer only loads the iOS head project and the two class libaries and the build is significantly quicker as it’s only building for iOS.


Next up is Android. Again by running the Launch.Android.bat you only see the Droid head project.

Windows (UWP)

Launch.Windows.bat will load the UWP project and again limit the build to only include the UWP target framework.

Web (WebAssembly / WASM)

The same process applies to WebAssembly (WASM).


Finally for MacOS, the bat files won’t work (since they won’t run on Mac). However, you can still manually adjust the TargetsToBuildDeveloperOverride property and set it to Mac.

Solution filters aren’t supported yet by visual Studio for Mac, so you may consider creating a Mac specific solution file, rather than having to load all of the projects.

One really neat feature I noticed as i was debugging on Mac is that the application automatically supports theming – here’s screenshot running in Light and Dark mode. This also works on the other platforms!!

Now you’ve been through it, make sure you check out the raw source code at the GitHub repository

Microsoft Build 2020: Uno Platform + WinUI = Future of Cross Platform Apps

I’ve been a long time supporter of the work that the team at Uno Platform have been doing. The announcement today of v3.0 of the Uno Platform comes hot on the heals of releases 2.3 and 2.4 that introduced AndroidX and MacOS support. This isn’t just any old announcement, v3 aligns the Uno Platform with … Continue reading “Microsoft Build 2020: Uno Platform + WinUI = Future of Cross Platform Apps”

I’ve been a long time supporter of the work that the team at Uno Platform have been doing. The announcement today of v3.0 of the Uno Platform comes hot on the heals of releases 2.3 and 2.4 that introduced AndroidX and MacOS support. This isn’t just any old announcement, v3 aligns the Uno Platform with the preview of WinUI 3.

At Built to Roam we’ve been building XAML based applications across a variety of technologies: WPF, Silverlight, WinPhone/Win8, UWP. Each iteration of Windows 10, new features were added to UWP but this limited the reach of the application to devices running the latest version of Windows 10. With WinUI 3.0 Microsoft is detaching the XAML platform away from the Windows version – this means that WinUI can iterate faster and bring newer controls and features to developers. In addition, WinUI also brings with it support for Win32 based applications – more on WinUI here.

So, why is it important that Uno Platform supports WinUI 3.0? Well, if you think of WinUI extending UWP to support all Windows 10 devices, then the addition of the Uno Platform takes WinUI across iOS, Android, macOS and Web via WebAssembly #WinUIEverywhere.

For more information, check out the Announcement of Uno Platform 3.0