Windows IoT Core application using Xamarin Forms


Screenshot of my first Windows 10 IoT Core Xamarin Forms application running on a Raspberry Pi 3. The app is the first exercise in Udemy’s Xamarin Forms course. The UWP build targeting Windows IoT Core was created following Adding a Universal Windows Platform (UWP) App. Take a look at how other native UWP IoT Core samples look and work. Also take a look at Xamarin Forms sample apps available at GitHub. You can also create an OS X application following Bringing macOS to Xamarin.Forms.


.NET Core class library solution from scratch

This post documents using the dotnet command to create a class library solution from scratch. The solution builds a class library project, and a MS unit test project that tests the class library.

To create an empty solution called MySolution.sln

dotnet new sln [--force] -n MySolution

sln is just one of several templates supported by the command. To see a list, try dotnet new -l. Additional templates can be installed using dotnet new --install e.g. AvaloniaUI.

To create a new class library project

dotnet new classlib [--force] -n MyLibrary

This creates a folder called MyLibrary and a MyLibrary.csproj file in it. Any C# files in the MyLibrary folder will be compiled during build.

If MyLibrary exists, use --force to replace the exiting project file.

If your project has an AssemblyInfo.cs that contains assembly attributes, you can edit project file to exclude autogeneration of assembly attributes

<Project Sdk="Microsoft.NET.Sdk">


    <PackageReference Include="Microsoft.CSharp" Version="4.4.0" />


Otherwise, you’ll get errors such as

obj/Debug/netcoreapp2.0/MyLibrary.AssemblyInfo.cs(10,12): error CS0579: Duplicate 'System.Reflection.AssemblyCompanyAttribute' attribute ...

Also, note the use of Microsoft.CSharp package in the project file. That is required to use C# language features such as dynamic. Without it, you’ll get an error such as

MyClass.cs(177,50): error CS0656: Missing compiler required member 'Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo.Create'

To add package reference, head into the MyLibrary project folder and run

dotnet add MyLibrary.csproj package Microsoft.CSharp

Then, run the following to restore package(s) from nuget

dotnet restore

Head over to the solution folder. To add the class library project to the solution, and build the solution

dotnet sln [MySolution.sln] add MyLibrary/MyLibrary.csproj
dotnet build

Specifying solution name is optional if you’ve got just one solution file in a folder.

To add a new MS unit test project

dotnet new mstest [--force] -n MyLibraryTest

Head into MyLibraryTest and add a reference to MyLibrary and package references

dotnet add MyLibraryTest.csproj reference ../MyLibrary/MyLibrary.csproj
dotnet add MyLibraryTest.csproj package Microsoft.CSharp
dotnet restore

Head over to the solution folder, build, and run unit tests

dotnet build
dotnet test MyLibraryTest

That wraps up the basic usage of dotnet to create and maintain a simple .NET Core class library project.

Self-signed code signing certificates

Some setup and application executables need to be signed so that they are not flagged as a security risk by security software on Windows. Especially those that have virus-like behavior such as embedded executable resources that are extracted, and executed.

The following steps were performed on Windows, from the Developer Command Prompt installed by Visual Studio.

To generate self-signed certificate for code signing, run

makecert.exe -n -r -h 0 -eku "," -e 12/31/2017 -pe -sv Test.pvk Test.cer

Here’s a brief overview of the command line
-n subject name
-r create self-signed certificate
-h max height of tree below this cert
-eku comma separated enhanced key usage ids
-e expiration date
-pe private key is exportable
-sv private key file name

You may specify a password or leave it empty.

To convert self-signed certificate to PFX format for usage with SignTool, run

Pvk2Pfx -pvk Test.pvk -spc Test.cer -pfx Test.pfx

To use SignTool to sign an executable, run

SignTool sign /fd SHA256 /a /f Test.pfx filepath.exe

Install certificate (Test.cer) to local machine before running executable.Screen Shot 2017-02-23 at 09.17.03.png

Signing a Wix Toolset setup bundle

You cannot just sign the setup bundle executable and get it to work, because the embedded executable (engine.exe) remains unsigned and will be flagged as a security risk. Use the following steps to prepare setup bundle for installation without being flagged as a security risk.

First, detach the engine from setup as follows

insignia -ib setup.exe -o engine.exe

Sign engine.exe with your certificate using SignTool

SignTool sign /fd SHA256 /a /f Test.pfx engine.exe

Re-attach the signed engine.exe to the bundle

insignia -ab engine.exe setup.exe -o setup.exe

Sign setup.exe with your certificate

SignTool sign /fd SHA256 /a /f Test.pfx setup.exe

JSON syntax highlighting in ScintillaNET

I am studying the excellent ScintillaNET code editing component, to enable basic JSON editing in a .NET application.

Inspired by the C# code highlighting example, here’s the code snippet to enable basic JSON syntax highlighting


Bluetooth serial client using Windows socket API

This post shows how you can discover paired Bluetooth devices, and communicate with them, using Windows socket API. The Windows socket API is available in .NET through the excellent 32feet.NET library.

This is how you can discover Bluetooth devices paired with Windows

client = new BluetoothClient();
devices = client.DiscoverDevices(10, true, true, false);

This is how you can connect with a device, and obtain a NetworkStream to read from

Guid MyServiceUuid = new Guid("{00001101-0000-1000-8000-00805F9B34FB}");
client.Connect(devices[0].DeviceAddress, MyServiceUuid);
NetworkStream stream = client.GetStream();

Here’s the implementation of ReadAsync

byte[] buffer = new byte[100];
while (true)
        int length = await stream.ReadAsync(buffer, 0, buffer.Length);
        // do something with buffer

The application can send data at any time as follows

stream.Write(buffer, 0, buffer.Length);

The code above is available at GitHub as part of the Bluetooth Serial Client Tool.


Bluetooth serial server using Windows socket API

This post describes a means to simulate a Bluetooth serial device on Windows. This can be useful to test Bluetooth applications running on Android and Windows, that use a virtual serial port to communicate with devices.

Windows Bluetooth socket API can be used to create a server (listener). I use 32feet.NET here, a neat .NET library layered over the C/C++ socket APIs provided by Microsoft.

Here’s how you can create a Bluetooth listener on the primary adapter/radio

Guid MyServiceUuid = new Guid("{00001101-0000-1000-8000-00805F9B34FB}");
BluetoothListener listener = new BluetoothListener(MyServiceUuid); // Listen on primary radio
listener.BeginAcceptBluetoothClient(acceptBluetoothClient, null);

The acceptBluetoothClient callback will be called when a client connects, and may be implemented as follows

if (listener == null) return;
client = listener.EndAcceptBluetoothClient(ar);
stream = client.GetStream();

ReadAsync is an async method that continuously receives data over the Bluetooth socket, and does something useful with it

byte[] buffer = new byte[100];
while (true)
        int length = await stream.ReadAsync(buffer, 0, buffer.Length);
        // do something useful with data in buffer

The application can send data at any time as follows

stream.WriteAsync(buffer, 0, buffer.Length);

As a bonus to the reader who’s come this far, the code above is available at GitHub as part of the Bluetooth Serial Server Tool.


Hello World with .NET Core

.NET Core is Microsoft’s new cross-platform Command Language Runtime (CLR). This post is an elementary getting started guide where I create, build and run a “Hello World!” console application with .NET Core.

Let’s begin by downloading and installing .NET Core for your platform. To create a new console applications run

dotnet new

That will create two files – project.csproj and Program.cs. Edit Program.cs using your favorite editor.

I recommend using the multi-platform VS Code. You can extend the capabilities of VS Code by downloading extensions from the VisualStudio Marketplace. VS Code should prompt you to download the C# extension when you open Program.cs.

To build the new program from the command line run

dotnet build

To execute the program run

dotnet run

You can also edit, and run or debug the program using VS Code, as shown in this screenshot

.NET CLR with VS Code

Console applications can be very powerful, but .NET CLR can also be used to build Web applications using ASP.NET Core.