AkiVaMu Just tiny things come to mind...

First .NET Core application

16 Oct 2018
Java DotNet

Create app

This post is similar to Getting started with .NET Core on Windows/Linux/macOS using the command line.

We will go step by step to create simple console app that run on .NET Core.

Install .NET core first, and then we go.

Prepare working dir

mkdir HelloDotnetCore
cd HelloDotnetCore

Initialize app from template

dotnet new console

Here we use dotnet tool to create a console application using template. It’s similar to Maven archetype, or Vue-CLI…

The command line output:

The template "Console Application" was created successfully.

Processing post-creation actions...
Running 'dotnet restore' on HelloDotnetCore.csproj...
  Restoring packages for HelloDotnetCore.csproj...
  Generating MSBuild file .\obj\HelloDotnetCore.csproj.nuget.g.props.
  Generating MSBuild file .\obj\HelloDotnetCore.csproj.nuget.g.targets.
  Restore completed in 174.98 ms for HelloDotnetCore.csproj.

Restore succeeded.

Notice the line:

Running 'dotnet restore' on HelloDotnetCore.csproj...

From official docs

The dotnet restore command uses NuGet to restore dependencies as well as project-specific tools that are specified in the project file

Yeah, dependency management, good! Just like Maven.

From .NET Core 2.0, the command dotnet new calls dotnet restore implicitly.

dotnet restore calls into NuGet (.NET package manager) to restore the tree of dependencies. NuGet analyzes the .csproj file, downloads the dependencies defined in the file (or grabs them from a cache on your machine), and writes the obj/project.assets.json file, which is necessary to compile and run the sample.

Project structure

Here is our folder content:

Program.cs
HelloDotnetCore.csproj
obj\
-- HelloDotnetCore.csproj.nuget.g.props
-- HelloDotnetCore.csproj.nuget.g.targets
-- HelloDotnetCore.csproj.nuget.cache
-- project.assets.json

First, Program.cs is our program source code.

obj folder is created when executing dotnet restore. We should ignore this folder in CVS.

Project file HelloDotnetCore.csproj

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

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp2.1</TargetFramework>
  </PropertyGroup>

</Project>

See Understanding the Project File.
In short, project file is used for build system, similar to maven pom.xml.

In MS world, there are MSBuild and dotnet CLI tool. See their relationship.
dotnet CLI tool uses MSBuild as its build engine.

Dependencies Management

NuGet is dependencies manager for .NET. It’s similar to maven in Java world, or npm in JavaScript.

Let’s add a dependency to our project: Newtonsoft.Json

dotnet add package Newtonsoft.Json --version 11.0.2

After executed, we can see these lines are added to our project file HelloDotnetCore.csproj:

<ItemGroup>
  <PackageReference Include="Newtonsoft.Json" Version="11.0.2" />
</ItemGroup>

Feel free to play with it in our code Program.cs.

Build and Run

We build the app by the command dotnet build:

dotnet build

Notice this command also executes dotnet restore, result:

Microsoft (R) Build Engine version 15.8.166+gd4e8d81a88 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

  Restore completed in 40.1 ms for HelloDotnetCore.csproj.
  HelloDotnetCore -> .\bin\Debug\netcoreapp2.1\HelloDotnetCore.dll

Build succeeded.

This command uses MSBuild under the hood.

The bin folder is created:

Debug
└───netcoreapp2.1
        HelloDotnetCore.deps.json
        HelloDotnetCore.dll
        HelloDotnetCore.pdb
        HelloDotnetCore.runtimeconfig.dev.json
        HelloDotnetCore.runtimeconfig.json
  • HelloDotnetCore.dll
    • Binary files in Intermediate Language (IL)
    • Wonder why .dll here? See this issue.
  • HelloDotnetCore.pdb
    • Symbol files for debugging
  • HelloDotnetCore.deps.json
    • List of the dependencies of the application.
    • You can see Newtonsoft.Json library is listed in this file.
  • HelloDotnetCore.runtimeconfig.json and HelloDotnetCore.runtimeconfig.dev.json
    • Specifies the shared runtime and its version for the application

Note: this build did NOT include external libraries (like Newtonsoft.Json from NuGet). So we can’t bring this output folder to another computer to run.

Run the app

dotnet .\bin\Debug\netcoreapp2.1\HelloDotnetCore.dll

You can actually build and run in one command:

dotnet run

Build for deployment

There are 2 types of deployment:

  • Framework-dependent deployments (FDD)
    • The app contains only its own code and any third-party dependencies
    • The system provides run-time environment
  • Self-contained deployments (SCD)
    • The app contains all code, libs and runtime

See tutorial Deploying .NET Core apps with command-line interface (CLI) tools

Framework-dependent deployments

dotnet publish -f netcoreapp2.1 -c Release

Similar to dotnet build, but with additional action: copy dependencies from the NuGet cache into the output folder.

We can see new folder Release and sub folder publish

Release
└─netcoreapp2.1
  └─publish
        HelloDotnetCore.deps.json
        HelloDotnetCore.dll
        HelloDotnetCore.pdb
        HelloDotnetCore.runtimeconfig.json
        Newtonsoft.Json.dll

Newtonsoft.Json.dll is copied to from NuGet cache to this folder.
Now we can bring this publish folder to another computer (with .NET Core 2.1 installed) and run.

Self-contained deployment

Publish with OS platform specified by -r params:

dotnet publish -r win10-x64 -c Release

We can see new folder win10-x64 in bin\Release\netcoreapp2.1\.

The publish folder contains a lot of files, included our application and .NET runtime.

Bring this publish folder to another computer (without any .NET runtime) and run .exe file

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