Microsoft's .NET Framework is a development platform that includes a Common Language Runtime (CLR) that manages the execution of code and a rich library of classes for building applications.

Microsoft designed the .NET Framework to have the possibility of being cross-platform, but Microsoft put their implementation effort into making it work best with Windows.

Practically speaking, the .NET Framework is Windows-only.

The open source community developed a cross-platform .NET implementation named the Mono project (http://www.mono-project.com/).

Mono is cross-platform, but it fell well behind Microsoft's implementation of .NET Framework. It has found a niche as the foundation of the Xamarin mobile platform.

Today, we live in a truly cross-platform world. Modern mobile and cloud development have made Windows a much less important operating system. So, Microsoft has been working on an effort to decouple the .NET Framework from its close ties with Windows.

While rewriting .NET to be truly cross-platform, Microsoft has taken the opportunity to refactor .NET, to remove major parts that are no longer considered "core".

This new product is branded as the .NET Core 1.0, which includes a cross-platform implementation of the CLR, known as CoreCLR , and a streamlined library of classes known as CoreFX.

Another .NET initiative is .NET Native which compiles C# code to native CPU instructions ahead-of-time (AoT) rather than using the CLR to compile IL just-in-time (JIT) to native code later.

The .NET Native compiler improves execution speed and reduces the memory footprint for applications. It supports the following:

The following table summarizes and compares Microsoft's three .NET technologies:

Start Notepad (or your favorite text editor) and enter the following code:

class Program { static void Main() { System.Console.
WriteLine("Hello C#!"); } }

You can type the code all on one line or spread it out over multiple lines and indent your lines to make it easier to read.

From the File menu, choose Save As.

In the dialog box, change to drive C: (or any drive that you want to use to save your projects), click on the New Folder button, and name the folder Code.

In the Save as type field, select All Files from the drop-down list to avoid appending the .txt file extension, and enter the file name as myfirstapp.cs, as shown in the following screenshot:

Your code in Notepad should look something like the following screenshot:

Start the Developer Command Prompt for VS2015 by typing the letters deve in the Windows 10 Search box, as you can see in the following screenshot. You will also find it on the Start Menu or Start Screen listed in All apps in the Visual Studio 2015 folder:

At the Command Prompt, enter the commands to do the following:

Here are the commands:

cd C:\Code
csc myfirstapp.cs
dir
myfirstapp

The output in the Command Prompt window should look like this:

Note that your source code, the file named myfirstapp.cs, has been compiled into an assembly named myfirstapp.exe. When you enter the name of the assembly, it is loaded and executed by .NET Framework 4.6 and its CLR.

You can copy the myfirstapp.exe file onto any computer with Windows 10 and it will run correctly because all copies of Windows 10 have .NET Framework 4.6 installed. Actually, you can copy the file onto a computer with an older version of Windows as long as it has .NET Framework 4.0 or later installed.

If the compiler displays errors, read them carefully, and fix them in Notepad. Save your changes and recompile.

A typical error might be using the wrong case, a missing semi-colon at the end of a line, or a mismatched pair of curly braces. For example, if you had mistyped a lowercase m for the Main method you would see this error message:

error CS5001: Program does not contain a static 'Main' method suitable for an entry point

The C# compiler converts your source code into Intermediate Language (IL) code and stores the IL in an assembly (a DLL or EXE file).

IL code statements are like assembly language instructions, but they are executed by the .NET virtual machine known as the Common Language Runtime (CLR).

At runtime, the CLR loads the IL code from the assembly, JIT compiles it into native CPU instructions, and then it is executed by the CPU on your machine.

The benefit of this two-step compilation process is that Microsoft can create CLRs for Linux and Mac OS X as well as for Windows. The same IL code runs everywhere because of the second compilation process that generates code for the native operating system and CPU instruction set.

Regardless of which language the source is written in, all .NET applications use IL code for their instructions, stored in an assembly. Microsoft provides a tool that can open an assembly and reveal this IL code.

Disassembling a compiled assembly is an advanced technique. I will walk you through the process, but do not worry about fully understanding what you are seeing yet!

Start the IL Disassembler by entering the following at the Developer Command Prompt:

ildasm myfirstapp.exe

You will see the IL DASM tool with the compiled EXE assembly loaded:

Double-click on MANIFEST in the tree view to show the metadata version (4.0.30319) of .NET and the Microsoft Core Library (mscorlib) assembly version (4.0.0.0) that this assembly needs to run. The following screenshot tells us that to run this assembly, we would need .NET Framework 4.0 or later installed:

Close the MANIFEST window, expand Program, and then double-click on the Main method. Note the IL instructions: ldstr (load string), nop (no operation), and ret (return). Remember that IL is an assembly language that is executed by the .NET CLR:

Anyone can use this tool to see any .NET assembly's IL code. Don't panic! This is not a reason to avoid C#.

All applications are lists of instructions that must be visible to the machine that runs it. If the machine can read these instructions, so can anything else. Therefore, all software can be reverse-engineered. It's just a matter of the effort required. .NET just happens to make it very easy!

Start Microsoft Visual Studio 2015.

Navigate to File | New | Project menu or press Ctrl + Shift + N.

At the top of the New Project dialog box, choose .NET Framework 4.6.1 (or later). From the Installed Templates list on the left, choose Visual C#. In the list at the center, choose Console Application. Enter the name Ch01_MyFirstApp, set the location to C:\Code, enter Chapter01 as the solution name, and click on OK or press Enter:

In the code editor, inside the Main method, press Enter to insert a new line between the innermost braces { }, and then type the letters sy, as you can see in the following screenshot:

Note that IntelliSense shows a list of keywords, namespaces, and types that contain the letters sy, and highlights the first one that starts with sy, which happens to be the namespace that we want—System.

Type a dot (also known as decimal point or full stop). IntelliSense automatically completes the word System for you, enters the dot, and displays a list of types and namespaces, such as AccessViolationException and Action, in the System namespace, as shown in the following screenshot:

Type the letters con and IntelliSense shows a list of matching types and namespaces:

Press the down arrow on your keyboard to highlight Console, and then type a dot.

IntelliSense shows a list of the members of the Console class:

Type the letters wr. IntelliSense shows two matching members containing these letters:

Use the down arrow to highlight WriteLine and then type an open parenthesis (.

IntelliSense autocompletes WriteLine and enters a pair of parentheses.

You will also see a tooltip telling you that the WriteLine method has 19 variations:

Type a double quote ("). IntelliSense enters a pair of double quotes for you and leaves the keyboard cursor in between them.

Type the text Hello C#!, as shown in the following screenshot:

The red squiggle at the end of the line indicates an error, because every C# statement must end in a semicolon. Move the cursor to the end of the line by pressing End, and type a semicolon to fix the error.

From the Debug menu, choose Start Without Debugging or press Ctrl + F5. Your completed application runs in a console window and closes when you press any key:

To save space and to make the output clearer, I will usually not include screenshots of output from console applications as I did previously. Instead, I will show the output like this:

Hello C#!

Let's make two deliberate errors.

Change the M of the Main method to the lowercase letter m.

Delete the e at the end of the method name WriteLine.

On the Build menu, choose Build Ch01_MyFirstApp or press Shift + F6.

After a few seconds, the status bar tells us that the build failed and the error list is activated. You can also view the error list by pressing Ctrl + W, E:

The Error List can be filtered to show Errors, Warnings, and informational Messages by clicking on the toggle buttons at the top of the window.

If an error shows the line number, for example Line 13 in the preceding screenshot, then you can double-click on the error to jump to the line causing the problem.

If it's a more general error, such as the missing Main method, the compiler can't tell you the line number. You might want a method named main as well as a method named Main (remember that C# is case sensitive so you're allowed to do that).

Fix the two (as shown in the preceding screenshot) errors before you continue. Note that the error list updates to show no errors.

Although Visual Studio has always had an Immediate window with limited REPL (read-eval-print loop) support, Visual Studio 2015 with Update 1 includes an enhanced window with full IntelliSense and color syntax code, named C# Interactive.

On the View menu, choose Other Windows, and then C# Interactive.

We will write some interactive code to download the About page from Microsoft's public website.

At the C# Interactive prompt, we will enter commands to do the following:

Type each of the following commands after the > prompt and then press Enter:

> #r "System.Net.Http"
> using System.Net.Http;
> var client = new HttpClient();
> client.BaseAddress = new Uri("http://www.microsoft.com/");
> var response = await client.GetAsync("about");
> response.StatusCode
OK
> response.Content.Headers.GetValues("Content-Type")
string[1] { "text/html" }
> await response.Content.ReadAsStringAsync()
"<!DOCTYPE html ><html xmlns:mscom=\"http://schemas.microsoft.com/CMSvNext\" xmlns:md=\"http://schemas.microsoft.com/mscom-data\" lang=\"en\" xmlns=\"http://www.w3.org/1999/xhtml\"><head><meta http-equiv=\"X-UA-Compatible\" content=\"IE=edge\" /><meta charset=\"utf-8\" /><meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\" /><link rel=\"shortcut icon\" href=\"//www.microsoft.com/favicon.ico?v2\" /><script type=\"text/javascript\" src=\"http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.7.2.min.js\">\r\n        // Third party scripts and code linked to or referenced from this website are licensed to you by the parties that own such code, not by Microsoft. See ASP.NET Ajax CDN Terms of Use - http://www.asp.net/ajaxlibrary/CDN.ashx.\r\n    </script><script type=\"text/javascript\" language=\"javascript\">/*<![CDATA[*/if($(document).bind(\"mobileinit\",function(){$.mobile.autoInitializePage=!1}),navigator.userAgent.match(/IEMobile\\/10\\.0/)){var msViewportStyle=document.createElement(\"style ...

Visual Studio has lots of other useful windows, including the following:

If you ever can't see a window you need, go to the View menu to make it reappear or learn its keyboard shortcut, as shown here:

To ensure that a project will work cross-platform, we can install and run the Visual Studio 2015 extension named .NET Portability Analyzer.

It allows you to choose multiple platforms that you would like to target and then scans your compiled assemblies, passes a list of the types and methods that you use to a web service, and produces a report that lists which ones are not supported on each platform along with recommendations for fixes.

Installing the .NET Portability Analyzer

In Visual Studio, go to the Tools menu and choose Extensions and Updates….

On the left-hand side of the dialog, click on Online. In the Search Visual Studio Gallery box, type portability and press Enter.

Click on the .NET Portability Analyzer entry and then click on the Download button. Once the extension is installed, restart Visual Studio:

Configuring the .NET Portability Analyzer

In Visual Studio, go to the Tools menu and choose Options.

In the Options dialog box, scroll down through the left-hand side list and choose .NET Portability Analyzer. In the Target Platforms section, deselect everything except for the following:

• .NET Core (Cross-platform) 1.0 (shown as 5.0 in the following screenshot)
• .NET Framework 4.5
• .NET Native 1.0
• ASP.NET Core 1.0 (shown as ASP.NET 5 in the screenshot below):

Tip

Microsoft Azure has a Platform-as-a-Service (PaaS) feature named Cloud Services, which is limited to the .NET Framework 4.5; this is why it is a common target platform to check with the analyzer.

Analyzing a solution

In Visual Studio, open the previous solution, named Chapter01. In the Solution Explorer window, right-click on the project named Ch01_MyFirstApp (not the solution), choose Analyze, and then choose Analyze Assembly Portability.

After a few seconds, a report will display in the main area.

Tip

Be patient with the .NET Portability Analyzer because it has to send data to a web service and wait for a response.

Note that the Console class in the System namespace and its WriteLine method are supported by the following:

• .NET Core (Cross-Platform) 1.0 (shown as 5.0 in the following screenshot)
• .NET Framework 4.5
• ASP.NET Core 1.0 (shown as ASP.NET 5 in the following screenshot)

However, it is not supported by .NET Native 1.0:

Note

At the time of writing this, the .NET Portability Analyzer has not been updated to show the new version branding for .NET Core and related products, which can be found at http://www.hanselman.com/blog/ASPNET5IsDeadIntroducingASPNETCore10AndNETCore10.aspx.

Press Ctrl + W, E to view the error list, which has also been populated. As we saw earlier, double-clicking on an error will jump the code editor to the line that could cause an issue:

Let's recreate the console application, but this time, target the .NET Core from the start.

Creating a .NET Core application using Command Line Tools

Start the Developer Command Prompt for VS2015. At the prompt, enter the following command:

dotnet

You should see the following output:

Enter the following at the prompt to create a new directory, change to it, create a new console application in the directory, and then list the files it created:

cd C:\Code\Chapter01
mkdir Ch01_MySecondApp
cd Ch01_MySecondApp
dotnet new
dir

You should see that the dotnet tool has created three new files for you: NuGet.Config, Program.cs, and project.json.

At the prompt, enter the following to start Notepad for editing the Program class:

notepad Program.cs

In Notepad, modify the WriteLine statement as follows:

Console.WriteLine("Hello C#, Welcome .NET Core!");

Save changes and exit Notepad.

At the prompt, enter the following commands:

dotnet restore
dotnet run

After a few seconds, all the dependency packages will be downloaded and your application will run, showing the following output:

To compile the source code into an assembly containing IL code, enter the following command:

dotnet build

The output in the Command Prompt window should look like this:

Enter the following commands to change to a subdirectory, list the files in it, and execute the compiled console application:

cd bin\Debug\dnxcore50
dir
Ch01_MySecondApp

Tip

The Debug is the name of the configuration and dnxcore50 is the name of the framework. This will change in the release version of the .NET Core.

Creating a .NET Core application using Visual Studio 2015

Start Visual Studio 2015 and open the Chapter01 solution.

In Visual Studio, navigate to File | Add | New Project.

In the Add New Project dialog box, in the Installed Templates list on the left-hand side, choose Visual C#. In the list at the center, choose Console Application (Package). Enter the name Ch01_DotNetCore, and click on OK or press Enter:

In the Solution Explorer window, right-click on the solution named Chapter01 and choose Properties.

Set the Startup Project to Current selection and click on OK.

Inside the Main method of the Program class, enter the following statements:

Console.WriteLine("Welcome, .NET Core!");
Console.ReadLine();

As you type code, you will notice that Visual Studio shows you which types and methods might not be available when targeting .NET Core. For example, the BufferHeight property is available when targeting the .NET Framework but not the .NET Core, as shown in the following screenshot as DNX 4.5.1 and DNX Core 5.0 respectively:

You can tell the compiler to include statements available only when .NET Framework is available by using conditional compilation symbols, as follows:

#if DNX451
    Console.BufferHeight = 300;
#elseif DNXCORE50
    // some alternative for .NET Core
#endif

Tip

In Chapter 5, Using Specialized .NET Types, you will learn more about conditional compilation symbols so that you can create projects that target both the .NET Framework and the .NET Core with a single code base.

Note

The names of the conditional compilation symbols will change in the future. Visit https://github.com/dotnet/corefx/blob/master/Documentation/architecture/net-platform-standard.md for more information.

In the Solution Explorer window, double-click on Properties for the Ch01_DotNetCore project.

In the Properties window, click on the Debug tab, select the Use Specific Runtime checkbox, and select the latest version of the .NET Core platform for the x64 CPU architecture, as shown in the following screenshot:

In the Visual Studio Debug menu, choose Start or press F5.

Note that the Command Prompt window shows that the console application is running the dnx-coreclr-win-x64.1.0.0-rc1-update1 runtime:

Tip

Throughout the first half of this book, I will show example code by creating console applications, so you can decide if you want to target the .NET Framework by choosing Console Application, or target the .NET Core by choosing Console Application (Package).

In Visual Studio, navigate to View | Team Explorer menu to see the Team Explorer window:

Although it is a good idea to sign up with an online source code management system provider, you can clone a GitHub repository without signing up for an account.

In the Team Explorer window, expand Local Git Repositories, click on the Clone menu, and then enter the following URL of a Git repository to clone it:

https://github.com/markjprice/cs6dotnetcore.git

Enter a path for the cloned Git repository:

C:\Code\Repos\cs6dotnetcore

Click on the Clone button:

Wait for the Git repository to clone locally:

You will now have a local copy of the complete solutions to all the hands-on practice exercises for this book.

Double-click on the cs6dotnetcore repo to open a detail view.

You can click on the options in the Project section to view Pull Requests and Issues, and other aspects of a repository.

You can double-click on an entry in the Solutions section to open it in the Solution Explorer:

Answer the following questions:

Practice closing and viewing windows, such as Error List and Toolbox.

You can pin, unpin, float, and rearrange windows by dragging their title bars. As you do so, Visual Studio will show blue tinted boxes and overlays to help you to understand where the window will be moved when you release the mouse button.

You do not need Visual Studio to practice writing C#. Simply go to the .NET Fiddle website (https://dotnetfiddle.net/) and start coding. It's also a great way to share snippets of C# code with other developers:

Use the following links to read more details about the topics covered in this chapter: