ASP.NET Core and Blazor updates in .NET Core 3.0 Preview 7

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ASP.NET Core and Blazor updates in .NET Core 3.0 Preview 7 - xSicKxBot - 07-26-2019

ASP.NET Core and Blazor updates in .NET Core 3.0 Preview 7

Daniel

July 23rd, 2019

.NET Core 3.0 Preview 7 is now available and it includes a bunch of new updates to ASP.NET Core and Blazor.

Here’s the list of what’s new in this preview:

Latest Visual Studio preview includes .NET Core 3.0 as the default runtime
Top level ASP.NET Core templates in Visual Studio
Simplified web templates
Attribute splatting for components
Data binding support for TypeConverters and generics
Clarified which directive attributes expect HTML vs C#
EventCounters
HTTPS in gRPC templates
gRPC Client Improvements
gRPC Metapackage
CLI tool for managing gRPC code generation

Please see the release notes for additional details and known issues.

Get started

To get started with ASP.NET Core in .NET Core 3.0 Preview 7 install the .NET Core 3.0 Preview 7 SDK

If you’re on Windows using Visual Studio, install the latest preview of Visual Studio 2019.

Note: .NET Core 3.0 Preview 7 requires Visual Studio 2019 16.3 Preview 1, which is being released later this week.

To install the latest client-side Blazor templates also run the following command:

Code:
dotnet new -i Microsoft.AspNetCore.Blazor.Templates::3.0.0-preview7.19365.7

Installing the Blazor Visual Studio extension is no longer required and it can be uninstalled if you’ve installed a previous version. Installing the Blazor WebAssembly templates from the command-line is now all you need to do to get them to show up in Visual Studio.

Upgrade an existing project

To upgrade an existing an ASP.NET Core app to .NET Core 3.0 Preview 7, follow the migrations steps in the ASP.NET Core docs.

Please also see the full list of breaking changes in ASP.NET Core 3.0.

To upgrade an existing ASP.NET Core 3.0 Preview 6 project to Preview 7:

Update Microsoft.AspNetCore.* package references to 3.0.0-preview7.19365.7.

That’s it! You should be ready to go.

Latest Visual Studio preview includes .NET Core 3.0 as the default runtime

The latest preview update for Visual Studio (16.3) includes .NET Core 3.0 as the default .NET Core runtime version. This means that if you install the latest preview of Visual Studio then you already have .NET Core 3.0. New project by default will target .NET Core 3.0

Top level ASP.NET Core templates in Visual Studio

The ASP.NET Core templates now show up as top level templates in Visual Studio in the “Create a new project” dialog.

This means you can now search for the various ASP.NET Core templates and filter by project type (web, service, library, etc.) to find the one you want to use.

Simplified web templates

We’ve taken some steps to further simplify the web app templates to reduce the amount of code that is frequently just removed.

Specifically:

The cookie consent UI is no longer included in the web app templates by default.
Scripts and related static assets are now referenced as local files instead of using CDNs based on the current environment.

We will provide samples and documentation for adding these features to new apps as needed.

Attribute splatting for components

Components can now capture and render additional attributes in addition to the component’s declared parameters. Additional attributes can be captured in a dictionary and then “splatted” onto an element as part of the component’s rendering using the new

Code:
@attributes

Razor directive. This feature is especially valuable when defining a component that produces a markup element that supports a variety of customizations. For instance if you were defining a component that produces an

Code:
<input>

element, it would be tedious to define all of the attributes

Code:
<input>

supports like

Code:
maxlength

Code:
placeholder

as component parameters.

Accepting arbitrary parameters

To define a component that accepts arbitrary attributes define a component parameter using the

Code:
[Parameter]

attribute with the

Code:
CaptureUnmatchedAttributes

property set to true. The type of the parameter must be assignable from

Code:
Dictionary<string, object>

. This means that

Code:
IEnumerable<KeyValuePair<string, object>>

Code:
IReadOnlyDictionary<string, object>

are also options.

Code:
@code { [Parameter(CaptureUnmatchedAttributes = true)] Dictionary<string, object> Attributes { get; set; }
}

The

Code:
CaptureUnmatchedAttributes

property on

Code:
[Parameter]

allows that parameter to match all attributes that do not match any other parameter. A component can only define a single parameter with

Code:
CaptureUnmatchedAttributes

.

Using @attributes to render arbitrary attributes

A component can pass arbitrary attributes to another component or markup element using the

Code:
@attributes

directive attribute. The

Code:
@attributes

directive allows you to specify a collection of attributes to pass to a markup element or component. This is valuable because the set of key-value-pairs specified as attributes can come from a .NET collection and do not need to be specified in the source code of the component.

Code:
<input class="form-field" @attributes="Attributes" type="text" /> @code { [Parameter(CaptureUnmatchedAttributes = true)] Dictionary<string, object> Attributes { get; set; }
}

Using the

Code:
@attributes

directive the contents of the

Code:
Attribute

property get “splatted” onto the input element. If this results in duplicate attributes, then evaluation of attributes occurs from left to right. In the above example if

Code:
Attributes

also contained a value for

Code:
class

it would supersede

Code:
class="form-field"

. If

Code:
Attributes

contained a value for

Code:
type

then that would be superseded by

Code:
type="text"

.

Data binding support for TypeConverters and generics

Blazor now supports data binding to types that have a string

Code:
TypeConverter

. Many built-in framework types, like

Code:
Guid

and

Code:
TimeSpan

have a string

Code:
TypeConverter

, or you can define custom types with a string

Code:
TypeConverter

yourself. These types now work seamlessly with data binding:

Code:
<input @bind="guid" /> <p>@guid</p> @code { Guid guid;
}

Data binding also now works great with generics. In generic components you can now bind to types specified using generic type parameters.

Code:
@typeparam T <input @bind="value" /> <p>@value</p> @code { T value;
}

Clarified which directive attributes expect HTML vs C

In Preview 6 we introduced directive attributes as a common syntax for Razor compiler related features like specifying event handlers (

Code:
@onclick

) and data binding (

Code:
@bind

). In this update we’ve cleaned up which of the built-in directive attributes expect C# and HTML. Specifically, event handlers now expect C# values so a leading

Code:
@

character is no longer required when specifying the event handler value:

Code:
@* Before *@
<button @onclick="@OnClick">Click me</button> @* After *@
<button @onclick="OnClick">Click me</button>

EventCounters

In place of Windows perf counters, .NET Core introduced a new way of emitting metrics via EventCounters. In preview7, we now emit EventCounters ASP.NET Core. You can use the

Code:
dotnet counters

global tool to view the metrics we emit.

Install the latest preview of

Code:
dotnet counters

by running the following command:

Code:
dotnet tool install --global dotnet-counters --version 3.0.0-preview7.19365.2

Hosting

The Hosting EventSourceProvider (

Code:
Microsoft.AspNetCore.Hosting

) now emits the following request counters:

Code:
requests-per-second
Code:
total-requests
Code:
current-requests
Code:
failed-requests

SignalR

In addition to hosting, SignalR (

Code:
Microsoft.AspNetCore.Http.Connections

) also emits the following connection counters:

Code:
connections-started
Code:
connections-stopped
Code:
connections-timed-out
Code:
connections-duration

To view all the counters emitted by ASP.NET Core, you can start dotnet counters and specify the desired provider. The example below shows the output when subscribing to events emitted by the

Code:
Microsoft.AspNetCore.Hosting

and

Code:
System.Runtime

providers.

Code:
dotnet counters monitor -p <PID> Microsoft.AspNetCore.Hosting System.Runtime

New Package ID for SignalR’s JavaScript Client in NPM

The Azure SignalR Service made it easier for non-.NET developers to make use of SignalR’s real-time capabilities. A frequent question we would get from potential customers who wanted to enable their applications with SignalR via the Azure SignalR Service was “does it only work with ASP.NET?” The former identity of the ASP.NET Core SignalR – which included the

Code:
@aspnet

organization on NPM, only further confused new SignalR users.

To mitigate this confusion, beginning with 3.0.0-preview7, the SignalR JavaScript client will change from being

Code:
@aspnet/signalr

Code:
@microsoft/signalr

. To react to this change, you will need to change your references in package.json files, require statements, and ECMAScript import statements. If you’re interested in providing feedback on this move or to learn the thought process the team went through to make the change, read and/or contribute to this GitHub issue where the team engaged in an open discussion with the community.

New Customizable SignalR Hub Method Authorization

With Preview 7, SignalR now provides a custom resource to authorization handlers when a hub method requires authorization. The resource is an instance of

Code:
HubInvocationContext

. The

Code:
HubInvocationContext

includes the

Code:
HubCallerContext

, the name of the hub method being invoked, and the arguments to the hub method.

Consider the example of a chat room allowing multiple organization sign-in via Azure Active Directory. Anyone with a Microsoft account can sign in to chat, but only members of the owning organization should be able to ban users or view users’ chat histories. Furthermore, we might want to restrict certain functionality from certain users. Using the updated features in Preview 7, this is entirely possible. Note how the

Code:
DomainRestrictedRequirement

serves as a custom

Code:
IAuthorizationRequirement

. Now that the

Code:
HubInvocationContext

resource parameter is being passed in, the internal logic can inspect the context in which the Hub is being called and make decisions on allowing the user to execute individual Hub methods.

Code:
public class DomainRestrictedRequirement : AuthorizationHandler<DomainRestrictedRequirement, HubInvocationContext>, IAuthorizationRequirement
{ protected override Task HandleRequirementAsync(AuthorizationHandlerContext context, DomainRestrictedRequirement requirement, HubInvocationContext resource) { if (IsUserAllowedToDoThis(resource.HubMethodName, context.User.Identity.Name) && context.User != null && context.User.Identity != null && context.User.Identity.Name.EndsWith("@jabbr.net", StringComparison.OrdinalIgnoreCase)) { context.Succeed(requirement); } return Task.CompletedTask; } private bool IsUserAllowedToDoThis(string hubMethodName, string currentUsername) { return !(currentUsername.Equals("bob42@jabbr.net", StringComparison.OrdinalIgnoreCase) && hubMethodName.Equals("banUser", StringComparison.OrdinalIgnoreCase)); }
}

Now, individual Hub methods can be decorated with the name of the policy the code will need to check at run-time. As clients attempt to call individual Hub methods, the

Code:
DomainRestrictedRequirement

handler will run and control access to the methods. Based on the way the

Code:
DomainRestrictedRequirement

controls access, all logged-in users should be able to call the

Code:
SendMessage

method, only users who’ve logged in with a

Code:
@jabbr.net

email address will be able to view users’ histories, and – with the exception of

Code:
bob42@jabbr.net

– will be able to ban users from the chat room.

Code:
[Authorize]
public class ChatHub : Hub
{ public void SendMessage(string message) { } [Authorize("DomainRestricted")] public void BanUser(string username) { } [Authorize("DomainRestricted")] public void ViewUserHistory(string username) { }
}

Creating the

Code:
DomainRestricted

policy is as simple as wiring it up using the authorization middleware. In

Code:
Startup.cs

, add the new policy, providing the custom

Code:
DomainRestrictedRequirement

requirement as a parameter.

Code:
services .AddAuthorization(options => { options.AddPolicy("DomainRestricted", policy => { policy.Requirements.Add(new DomainRestrictedRequirement()); }); });

It must be noted that in this example, the

Code:
DomainRestrictedRequirement

class is not only a

Code:
IAuthorizationRequirement

but also it’s own

Code:
AuthorizationHandler

for that requirement. It is fine to split these into separate classes to separate concerns. Yet, in this way, there’s no need to inject the

Code:
AuthorizationHandler

during

Code:
Startup

, since the requirement and the handler are the same thing, there’s no need to inject the handler separately.

HTTPS in gRPC templates

The gRPC templates have been now been updated to use HTTPS by default. At development time, we continue the same certificate generated by the

Code:
dotnet dev-certs

tool and during production, you will still need to supply your own certificate.

gRPC Client Improvements

The managed gRPC client (

Code:
Grpc.Net.Client

) has been updated to target .NET Standard 2.1 and no longer depends on types present only in .NET Core 3.0. This potentially gives us the ability to run on other platforms in the future.

gRPC Metapackage

In 3.0.0-preview7, we’ve introduced a new package

Code:
Grpc.AspNetCore

that transitively references all other runtime and tooling dependencies required for building gRPC projects. Reasoning about a single package version for the metapackage should make it easier for developers to deal with as opposed multiple dependencies that version independently.

CLI tool for managing gRPC code generation

The new

Code:
dotnet-grpc

global tool makes it easier to manage protobuf files and their code generation settings. The global tool manages adding and removing protobuf files as well adding the required package references required to build and run gRPC applications.

Install the latest preview of

Code:
dotnet-grpc

by running the following command:

Code:
dotnet tool install --global dotnet-grpc --version 0.1.22-pre2

As an example, you can run following commands to generate a protobuf file and add it to your project for code generation. If you attempt this on a non-web project, we will default to generating a client and add the required package dependencies.

Code:
dotnet new proto -o .\Protos\mailbox.proto
dotnet grpc add-file .\Protos\mailbox.proto

Give feedback

We hope you enjoy the new features in this preview release of ASP.NET Core and Blazor! Please let us know what you think by filing issues on GitHub.

Thanks for trying out ASP.NET Core and Blazor!

Daniel Roth

Principal Program Manager, ASP.NET

Follow Daniel https://devblogs.microsoft.com/aspnet/author/danroth27/feed/