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Installing 3.0 Preview 3 SDK broke build for 3.0 Preview 2 Razor Components app

See original GitHub issue

I created an app with the Preview 2 SDK (released bits). Today I installed the latest available Preview 3 bits ( and now I get build errors for the Razor Components cshtml files. I’m not sure if this is expected, since there have been a lot of changes in this area between Preview 2 and Preview 3.

Installation reported these bits, for context:

The following were installed at: ‘C:\Program Files\dotnet’ • .NET Core SDK 3.0.100-preview3-010343 • .NET Core Runtime 3.0.0-preview3-27421-7 • ASP.NET Core Runtime 3.0.0-preview3-19121-17 • .NET Core Windows Desktop Runtime 3.0.0-preview3-27420-40

The build errors I get are like this one (note, it’s in a generated file for the .cshtml):

obj\Debug\netstandard2.0\Razor\Pages\Counter.cshtml.g.cs(35,48): error CS0234: The type or namespace name ‘EventCallback’ does not exist in the namespace ‘Microsoft.AspNetCore.Components’ (are you missing an assembly reference?) [D:\src\AppBuilding\src\OrderSite.App\OrderSite.App.csproj]

The generated line of code is:

builder.AddAttribute(7, "onclick", Microsoft.AspNetCore.Components.EventCallback.Factory.Create<Microsoft.AspNetCore.Components.UIMouseEventArgs>(this, IncrementCount));

With the Preview 2 SDK, the generated line of code was:

builder.AddAttribute(7, "onclick", Microsoft.AspNetCore.Components.BindMethods.GetEventHandlerValue<Microsoft.AspNetCore.Components.UIMouseEventArgs>(IncrementCount));

Note: if I create a new Razor Components project with the Preview 3 SDK installed, it builds fine. The project created is very different from the Preview 2 template however.

Issue Analytics

  • State:closed
  • Created 5 years ago
  • Comments:8 (3 by maintainers)

github_iconTop GitHub Comments

rynowakcommented, Feb 22, 2019

This is expected for now.

We’re still working on the compiler and there will be changes between releases. We don’t expect the runtime from preview2 to be compatible with a nightly build of the SDK.

mitsuakiwatanabecommented, Aug 15, 2019

@DefenceAquireSustain I had the same problem. but I read this news and solved it.

Remove use of namespace Microsoft.AspNetCore.Components.Layouts.

In Razor components rename OnInit to OnInitialized and OnInitAsync to OnInitializedAsync.

Read more comments on GitHub >

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