You should rarely have to call these methods at all, as you should use constructor injection where ever possible. 

In rare cases, such as factories or to dynamically instantiate command handlers, you can resolve it yourself.

That being said, you should use `GetRequiredService` where you **require** the service. It will throw an exception, when the service is not registered. 

`GetService` on the other side is for **optional** dependencies, which will just return `null` when there is no such service registered. 

The difference is that `GetService&lt;T&gt;()` returns `null` if it can&#39;t find the service. `GetRequiredService&lt;T&gt;()` throws an `InvalidOperationException` instead.

I&#39;m trying to bottom-center a widget at the bottom of a Column, but it keeps aligning to the left.

    return new Column(
      new Stack(
        new Positioned(
          bottom: 0.0, 
          new Center(
            new Container(),
          ),
        ),
      ),
    ); 

The existence of the Positioned forces the Container to the left, instead of centering. Removing the Positioned, however, puts the Container in the middle-center.

Flutter: Trying to bottom-center an item in a Column, but it keeps left-aligning

The documentation of [`docker ps`](https://docs.docker.com/engine/reference/commandline/ps/) and [`docker container ls`](https://docs.docker.com/engine/reference/commandline/container_ls/) both says &quot;List containers&quot;, but does not mention the other command. Is there a difference between those two commands?

The output looks exactly the same:

    CONTAINER ID        IMAGE                      COMMAND                  CREATED             STATUS              PORTS                    NAMES
    bbe3d7158eaa        flaskmysqldockerized_web   &quot;python app.py&quot;          5 hours ago         Up 18 seconds       0.0.0.0:8082-&gt;5000/tcp   flaskmysqldockerized_web_1
    4f7d3f0763ad        mysql                      &quot;docker-entrypoint...&quot;   6 hours ago         Up 18 seconds       0.0.0.0:3307-&gt;3306/tcp   flaskmysqldockerized_db_1


Is there a difference between &quot;docker ps&quot; and &quot;docker container ls&quot;?

What are the differences between `IServiceProvider.GetRequiredService()` and `IServiceProvider.GetService()`?

When is it a better idea to use `GetRequiredService()`? 

On IServiceProvider what are the differences between the GetRequiredService and GetService methods?

<p>What are the differences between <code>IServiceProvider.GetRequiredService()</code> and <code>IServiceProvider.GetService()</code>?</p>
<p>When is it a better idea to use <code>GetRequiredService()</code>?</p>


Two design patterns namely Dependency Injection and Dependency Inversion exist out there, Articles are there in the net trying to explain the difference. But the need to explain it in easier words is still there. Any one  out there to come up to ?

I need to understand it in PHP.

Difference between dependency injection and dependency inversion

In my ASP.NET Core application, I get the following error:

&gt; InvalidOperationException: Unable to resolve service for type &#39;Cities.Models.IRepository&#39; while attempting to activate &#39;Cities.Controllers.HomeController&#39;.

I the `HomeController` I am trying to pass the `Cities` getter to the view like so:

``` c#
public class HomeController : Controller
{
    private readonly IRepository repository;

    public HomeController(IRepository repo) =&gt; repository = repo;

    public IActionResult Index() =&gt; View(repository.Cities);
}
```


I have one file `Repository.cs` that contains an interface and its implementation like so:

``` c#
public interface IRepository
{
    IEnumerable&lt;City&gt; Cities { get; }
    void AddCity(City newCity);
}

public class MemoryRepository : IRepository
{
    private readonly List&lt;City&gt; cities = new List&lt;City&gt;();

    public IEnumerable&lt;City&gt; Cities =&gt; cities;

    public void AddCity(City newCity) =&gt; cities.Add(newCity);
}
```

My `Startup` class contains the default-generated code from the template. I have made any changes:

``` c#
public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddControllersWithViews();
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        ...
    }
}
```

Unable to resolve service for type while attempting to activate

I use in kotlin activity ViewPager and I want in Kotlin Fragment use the dagger injection. I have got Error: Dagger does not support injection into private fields.
In Java Fragment the dagger injection work.
Why can i not inject dagger in kotlin faragment ?

in my kotlin activity

    mPagerAdapter = object : FragmentPagerAdapter(supportFragmentManager) {

            private val mFragments = arrayOf(KotlinFragment(), JavaFragment())
            private val mFragmentNames = arrayOf(getString(R.string.cashdocuments), getString(R.string.action_absmysql))

            override fun getItem(position: Int): Fragment {
                return mFragments[position]
            }

            override fun getCount(): Int {
                return mFragments.size
            }

            override fun getPageTitle(position: Int): CharSequence {
                return mFragmentNames[position]
            }
        }

my kotlin fragment

    class KotlinFragment : Fragment()  {


    @Inject
    internal var mSharedPreferences: SharedPreferences? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        (activity.application as SamfantozziApp).dgaeacomponent().inject(this)

    }

    override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        super.onCreateView(inflater, container, savedInstanceState)
        val rootView = inflater!!.inflate(R.layout.activity_absserver, container, false)
        
        return rootView
    }
    
    }

messages gradle build

[![enter image description here][1]][1]


  [1]: https://i.stack.imgur.com/WDYxt.png

Kotlin Error: Dagger does not support injection into private fields

My understanding is that when using the built in the dependency injection, a .NET Core console app will require you to create and manage all scopes yourself whereas a ASP.NET Core app will create and manage the `HttpRequest` scope by default through defined middleware(s). 

With ASP.NET Core, you can optionally create and manage your own scopes that by calling `CreateScope()` for when you need services that live outside of a `HttpRequest`.

It is clear that calling `IServiceScopeFactory.CreateScope()` will create a new `IServiceScope` every time; however, does calling the `IServiceProvider.CreateScope()` extension method also create a new `IServiceScope` every time?

Basically, is there a meaningful difference between the following ways to create scope in both ASP.NET Core and .NET Core console apps:

    public class Foo()
    {
        public Foo(IServiceProvider serviceProvider)
        {
            using(var scope = serviceProvider.CreateScope())
            {   
                scope.ServiceProvider.GetServices&lt;&gt;();           
            }
        }
    }


and

    public class Bar()
    {
        public Bar(IServiceScopeFactory scopeFactory)
        {
            using(var scope = scopeFactory.CreateScope())
            {   
                scope.ServiceProvider.GetServices&lt;&gt;();           
            }
        }
    }



.NET Core IServiceScopeFactory.CreateScope() vs IServiceProvider.CreateScope() extension

What is the proper way to register a custom hosted service in ASP.NET Core 2.1? For example, I have a custom hosted service derived from [BackgroundService](https://docs.microsoft.com/en-us/dotnet/api/microsoft.extensions.hosting.backgroundservice?view=aspnetcore-2.1) named `MyHostedService`. How should I register it?

    public IServiceProvider ConfigureServices(IServiceCollection services)
    {           
        //...
        services.AddSingleton&lt;IHostedService, MyHostedService&gt;();
    }

or

    public IServiceProvider ConfigureServices(IServiceCollection services)
    {           
        //...
        services.AddHostedService&lt;MyHostedService&gt;();
    }

?

[Here](https://blogs.msdn.microsoft.com/cesardelatorre/2017/11/18/implementing-background-tasks-in-microservices-with-ihostedservice-and-the-backgroundservice-class-net-core-2-x/) we can see the first case, but [here](https://docs.microsoft.com/en-us/aspnet/core/fundamentals/host/hosted-services?view=aspnetcore-2.1) there is a second case.

Are these methods equal?

Proper way to register HostedService in ASP.NET Core. AddHostedService vs AddSingleton

In some reason, I need to use SQL in EFCore, and I will use table name of mapped entity. How can I get it?

How to get Table Name of mapped entity in Entity Framework Core

I&#39;m trying to migrate my auth stuff to Core 2.0 and having an issue using my own authentication scheme. My service setup in startup looks like this:

    var authenticationBuilder = services.AddAuthentication(options =&gt;
    {
    	options.AddScheme(&quot;myauth&quot;, builder =&gt;
    	{
    		builder.HandlerType = typeof(CookieAuthenticationHandler);
    	});
    })
    	.AddCookie();

My login code in the controller looks like this:

    var claims = new List&lt;Claim&gt;
    {
    	new Claim(ClaimTypes.Name, user.Name)
    };
    
    var props = new AuthenticationProperties
    {
    	IsPersistent = persistCookie,
    	ExpiresUtc = DateTime.UtcNow.AddYears(1)
    };
    
    var id = new ClaimsIdentity(claims);
    await HttpContext.SignInAsync(&quot;myauth&quot;, new ClaimsPrincipal(id), props);

But when I&#39;m in a controller or action filter, I only have one identity, and it&#39;s not an authenticated one:

    var identity = context.HttpContext.User.Identities.SingleOrDefault(x =&gt; x.AuthenticationType == &quot;myauth&quot;);

Navigating these changes has been difficult, but I&#39;m guessing that I&#39;m doing .AddScheme wrong. Any suggestions?

EDIT: Here&#39;s (essentially) a clean app that results not in two sets of Identities on User.Identies:

    namespace WebApplication1.Controllers
    {
        public class Testy : Controller
        {
    	    public IActionResult Index()
    	    {
    		    var i = HttpContext.User.Identities;
    		    return Content(&quot;index&quot;);
    	    }
    
    	    public async Task&lt;IActionResult&gt; In1()
    	    {
    			var claims = new List&lt;Claim&gt; { new Claim(ClaimTypes.Name, &quot;In1 name&quot;) };
    		    var props = new AuthenticationProperties  { IsPersistent = true, ExpiresUtc = DateTime.UtcNow.AddYears(1) };
    		    var id = new ClaimsIdentity(claims);
    		    await HttpContext.SignInAsync(CookieAuthenticationDefaults.AuthenticationScheme, new ClaimsPrincipal(id), props);
    		    return Content(&quot;In1&quot;);
    		}
    
    	    public async Task&lt;IActionResult&gt; In2()
    	    {
    		    var claims = new List&lt;Claim&gt; { new Claim(ClaimTypes.Name, &quot;a2 name&quot;) };
    		    var props = new AuthenticationProperties { IsPersistent = true, ExpiresUtc = DateTime.UtcNow.AddYears(1) };
    		    var id = new ClaimsIdentity(claims);
    		    await HttpContext.SignInAsync(&quot;a2&quot;, new ClaimsPrincipal(id), props);
    		    return Content(&quot;In2&quot;);
    	    }
    
    	    public async Task&lt;IActionResult&gt; Out1()
    	    {
    		    await HttpContext.SignOutAsync(CookieAuthenticationDefaults.AuthenticationScheme);
    		    return Content(&quot;Out1&quot;);
    		}
    
    	    public async Task&lt;IActionResult&gt; Out2()
    	    {
    		    await HttpContext.SignOutAsync(&quot;a2&quot;);
    		    return Content(&quot;Out2&quot;);
    	    }
    	}
    }

And Startup:

    namespace WebApplication1
    {
        public class Startup
        {
            public Startup(IConfiguration configuration)
            {
                Configuration = configuration;
            }
    
            public IConfiguration Configuration { get; }
    		
            public void ConfigureServices(IServiceCollection services)
            {
    			services.AddAuthentication(options =&gt;
    			{
    				options.DefaultScheme = CookieAuthenticationDefaults.AuthenticationScheme;
    		        })
    		        .AddCookie(CookieAuthenticationDefaults.AuthenticationScheme)
    		        .AddCookie(&quot;a2&quot;);
    
    			services.AddMvc();
            }
    		
            public void Configure(IApplicationBuilder app, IHostingEnvironment env)
            {
                app.UseAuthentication();
    
                app.UseMvc(routes =&gt;
                {
                    routes.MapRoute(name: &quot;default&quot;, template: &quot;{controller=Home}/{action=Index}/{id?}&quot;);
                });
            }
        }
    }




How do I setup multiple auth schemes in ASP.NET Core 2.0?

In MVC, we have used the following code to download a file. In ASP.NET core, how to achieve this?

```csharp
    HttpResponse response = HttpContext.Current.Response;                 
    System.Net.WebClient net = new System.Net.WebClient();
    string link = path;
    response.ClearHeaders();
    response.Clear();
    response.Expires = 0;
    response.Buffer = true;
    response.AddHeader(&quot;Content-Disposition&quot;, &quot;Attachment;FileName=a&quot;);
    response.ContentType = &quot;APPLICATION/octet-stream&quot;;
    response.BinaryWrite(net.DownloadData(link));
    response.End();
```

How to download a file in ASP.NET Core?

After upgrading to ASP.NET Core 2.0, I can&#39;t seem to create migrations anymore.

I&#39;m getting 

&gt; &quot;An error occurred while calling method &#39;BuildWebHost&#39; on class
&gt; &#39;Program&#39;. Continuing without the application service provider. Error:
&gt; One or more errors occurred. (Cannot open database &quot;...&quot; requested by
&gt; the login. The login failed. Login failed for user &#39;...&#39;&quot;

and

&gt; &quot;Unable to create an object of type &#39;MyContext&#39;. Add an implementation
&gt; of &#39;IDesignTimeDbContextFactory&lt;MyContext&gt;&#39; to the project, or see
&gt; https://go.microsoft.com/fwlink/?linkid=851728 for additional patterns
&gt; supported at design time.&quot;

The command I previously ran was `$ dotnet ef migrations add InitialCreate --startup-project &quot;..\Web&quot; ` (from the project/folder with the DBContext).

Connection string: `&quot;Server=(localdb)\\mssqllocaldb;Database=database;Trusted_Connection=True;MultipleActiveResultSets=true&quot;`


This is my Program.cs

     public class Program
    {
        public static void Main(string[] args)
        {
            BuildWebHost(args).Run();
        }

        public static IWebHost BuildWebHost(string[] args) =&gt;
           WebHost.CreateDefaultBuilder(args)
               .UseStartup&lt;Startup&gt;()
               .Build();
    }
 


Unable to create migrations after upgrading to ASP.NET Core 2.0

I have the following class in NET Core2.0 App.

    // required when local database does not exist or was deleted
    public class ToDoContextFactory : IDesignTimeDbContextFactory&lt;AppContext&gt;
    {
        public AppContext CreateDbContext(string[] args)
        {
            var builder = new DbContextOptionsBuilder&lt;AppContext&gt;();
            builder.UseSqlServer(&quot;Server=localhost;Database=DbName;Trusted_Connection=True;MultipleActiveResultSets=true&quot;);
            return new AppContext(builder.Options);
        }
    }

This is required in Core 2.0 with migration when Database does not exist and has to be created when you run *update-database*.&lt;br&gt;
[https://stackoverflow.com/questions/45782446/unable-to-create-migrations-after-upgrading-to-asp-net-core-2-0][1]

I would like not having ConnectionString in 2 places(here and in appsettings.json) but only in .json
so I have tried to replace

    &quot;Server=localhost;Database=DbName;Trusted_Connection=True;MultipleActiveResultSets=true&quot;

with

    ConfigurationManager.ConnectionStrings[&quot;DefaultConnection&quot;].ConnectionString

but it&#39;s not working, I&#39;m getting null value.

UPDATE 1:&lt;br&gt;
Just to note that adding explicitly .json is not necessery in Core 2 so the problem is not with the file.&lt;br&gt;
[https://andrewlock.net/exploring-program-and-startup-in-asp-net-core-2-preview1-2/][2]&lt;br&gt;
&lt;br&gt;
UPDATE 2:&lt;br&gt;
Also I am already using Configuration for sending ConnectionString from .json to Context:

    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }
    
        public IConfiguration Configuration { get; }
    
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddDbContext&lt;AppContext&gt;(options =&gt; options.UseSqlServer(Configuration.GetConnectionString(&quot;DefaultConnection&quot;)));
        }
    }

But I can not use this for *ToDoContextFactory* because it does not have Configuration, and *ToDoContextFactory* is used by migrations so the App is not running at all.&lt;br&gt;

SOLUTION:
Based on answer from @JRB I made it work like this:

    public AppContext CreateDbContext(string[] args)
    {
        string projectPath = AppDomain.CurrentDomain.BaseDirectory.Split(new String[] { @&quot;bin\&quot; }, StringSplitOptions.None)[0];
        IConfigurationRoot configuration = new ConfigurationBuilder()
            .SetBasePath(projectPath)
            .AddJsonFile(&quot;appsettings.json&quot;)
            .Build();
        string connectionString = configuration.GetConnectionString(&quot;DefaultConnection&quot;);
    
        var builder = new DbContextOptionsBuilder&lt;AppContext&gt;();
        builder.UseSqlServer(connectionString);
        
        return new AppContext(builder.Options);
    }


  [1]: https://stackoverflow.com/questions/45782446/unable-to-create-migrations-after-upgrading-to-asp-net-core-2-0
  [2]: https://andrewlock.net/exploring-program-and-startup-in-asp-net-core-2-preview1-2/

Get ConnectionString from appsettings.json instead of being hardcoded in .NET Core 2.0 App

I&#39;ve been on quite an adventure to get JWT working on DotNet core 2.0 (now reaching final release today).  There is a *ton* of documentation, but all the sample code seems to be using deprecated APIs and coming in fresh to Core, It&#39;s positively dizzying to figure out how exactly it&#39;s supposed to be implemented. I tried using Jose, but app. UseJwtBearerAuthentication has been deprecated, and there is no documentation on what to do next.

Does anyone have an open source project that uses dotnet core 2.0 that can simply parse a JWT from the authorization header and allow me to authorize requests for a HS256 encoded JWT token?

The class below doesn&#39;t throw any exceptions, but no requests are authorized, and I get no indication _why_ they are unauthorized.  The responses are empty 401&#39;s, so to me that indicates there was no exception, but that the secret isn&#39;t matching.

One odd thing is that my tokens are encrypted with the HS256 algorithm, but I see no indicator to tell it to force it to use that algorithm anywhere.

Here is the class I have so far:

	using System;
	using System.Collections.Generic;
	using System.IO;
	using Microsoft.AspNetCore.Authentication;
	using Microsoft.AspNetCore.Authentication.JwtBearer;
	using Microsoft.AspNetCore.Builder;
	using Microsoft.AspNetCore.Hosting;
	using Microsoft.AspNetCore.Http;
	using Microsoft.Extensions.Configuration;
	using Microsoft.Extensions.DependencyInjection;
	using Microsoft.Net.Http.Headers;
	using Newtonsoft.Json.Linq;
	using Microsoft.IdentityModel.Tokens;
	using System.Text;

	namespace Site.Authorization
	{
		public static class SiteAuthorizationExtensions
		{
			public static IServiceCollection AddSiteAuthorization(this IServiceCollection services)
			{
				var signingKey = new SymmetricSecurityKey(Encoding.ASCII.GetBytes(&quot;SECRET_KEY&quot;));

				var tokenValidationParameters = new TokenValidationParameters
				{
					// The signing key must match!
					ValidateIssuerSigningKey = true,
					ValidateAudience = false,
					ValidateIssuer = false,
					IssuerSigningKeys = new List&lt;SecurityKey&gt;{ signingKey },


					// Validate the token expiry
					ValidateLifetime = true,
				};

				services.AddAuthentication(options =&gt;
				{
					options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
					options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;


				})
				
				.AddJwtBearer(o =&gt;
				{
					o.IncludeErrorDetails = true;
					o.TokenValidationParameters  = tokenValidationParameters;
					o.Events = new JwtBearerEvents()
					{
						OnAuthenticationFailed = c =&gt;
						{
							c.NoResult();

							c.Response.StatusCode = 401;
							c.Response.ContentType = &quot;text/plain&quot;;

							return c.Response.WriteAsync(c.Exception.ToString());
						}

					};
				});

				return services;
			}
		}
	}

JWT on .NET Core 2.0

I was reading the announcement of entity framework core 2.0 https://blogs.msdn.microsoft.com/dotnet/2017/08/14/announcing-entity-framework-core-2-0/

It says that they added new Sql functions like `EF.Functions.Like` for performing the SQL `LIKE` operation.

I was wondering, what then would be the difference between `EF.Functions.Like` and `string.Contains`/`StartsWith`?

For example:

    var customers = context.Customers.Where(c =&gt; c.Name.StartsWith(&quot;a&quot;)); // Version A
    var customers = context.Customers.Where(c =&gt; EF.Functions.Like(c.Name, &quot;a%&quot;)); // Version B

What would be the difference between the two versions? 
EF already knows how to translate `string.Contains`/`StartsWith` to the corresponding SQL operations, doesn&#39;t it?

The only reason i can think of is that EF.Functions.Like would allow for more complex patterns like `&quot;a%b%&quot;` (although this one can be written as `StartsWith(&quot;a&quot;) &amp;&amp; Contains(&quot;b&quot;)`)

Is this the reason?

Entity framework EF.Functions.Like vs string.Contains

I use visual studio to update all my environments with a certain migration. It had worked fine using the command below.
     
    update-database -Migration initMigrationProduct -c ProductContext -Environment Production

In ef core 2.0 this command has been changed and parameter -Environment has been removed. In the docs it said.

&gt; &quot;With 2.0, you can use the ASPNETCORE_ENVIRONMENT environment variable
&gt; instead.&quot;

 
https://docs.microsoft.com/en-us/ef/core/miscellaneous/cli/dotnet

I have now tried all kinds of ways but when I run the `update-database` with ef core 2.0 it doesn&#39;t use the `ASPNETCORE_ENVIRONMENT` variable. I tried to set in registry, application properties. 

Please let me know what I need to do to get this working to update different environments?

If I start the application with different `launchsettings` it works but not using the package manager console.

ef core doesn&#39;t use ASPNETCORE_ENVIRONMENT during update-database

In the following console application (.Net core 2.0), the `scaffold-dbcontext` created the following `DbContext`

    public partial class MyContext : DbContext
    {
        public virtual DbSet&lt;Tables&gt; Tables { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            if (!optionsBuilder.IsConfigured) { optionsBuilder.UseSqlServer(Program.Conn); }
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder) { .... }
    }

In the Main() (`static void Main(string[] args)`), the following code

    var services = new ServiceCollection();
    var conn = configuration.GetConnectionString(&quot;MySource&quot;);
    services.AddDbContext&lt;MyContext&gt;(o =&gt; o.UseSqlServer(conn)); // Error

got the following run-time error? 

&gt; AddDbContext was called with configuration, but the context type &#39;MyContext&#39; only declares a parameterless constructor. This means that the configuration passed to AddDbContext will never be used

Content Type	Original Author	Original Content on Stackoverflow
Question	Art Base	View Question on Stackoverflow
Solution 1 - Dependency Injection	Tseng	View Answer on Stackoverflow
Solution 2 - Dependency Injection	tchelidze	View Answer on Stackoverflow

On IServiceProvider what are the differences between the GetRequiredService and GetService methods?

Dependency Injection Problem Overview

Dependency Injection Solutions

Solution 1 - Dependency Injection

Solution 2 - Dependency Injection

Is there a difference between "docker ps" and "docker container ls"?

Flutter: Trying to bottom-center an item in a Column, but it keeps left-aligning

Attributions