Blazor-Component inherits from BaseClass

Question

i am about to create a Base-Class for my Razor-Components. This Base-Class looks like:

public abstract class ExampleBase : ComponentBase 
{
    public virtual void Submit()
    {
        //DoSomething
    }

    public virtual void Back()
    {
        //DoSomething else
    }
}

my Blazor-Component inherits from this class

@inherits ExampleBase

<button @onclick="Submit" />

So far so good, but when i start my App and this Page is about to Load then i receive an Exception:

[2020-09-29T12:09:03.920Z] Error: System.ArgumentException: The component type must implement Microsoft.AspNetCore.Components.IComponent. at Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder.OpenComponent(Int32 sequence, Type componentType)

what is wrong on being inherited from ComponentBase ?

Thanks for your help

Addition: I call my Razor-Component like this and the Exception throws at builder.OpenComponent

RenderFragment CreateFragment() => builder =>
{
  builder.OpenComponent(0, typeof(MyRazorComponent));
  builder.CloseComponent();
}

Hope this helps

Answer 1

First of all - Thank you all for you're help i really appreciate!

After a few hours break. I found my own mistake...

What i am doing: i've created a service which loads a List of Type List this service gets inject in a Razor-Component.

The code of service:

//this returns a listOfRazorComponents
return AppDomain.CurrentDomain.GetAssemblies()
            .Where(x => x.FullName.StartsWith("SampleApplication")).FirstOrDefault()
            .DefinedTypes.Where(x=>x.BaseType is ComponentBase);

In my Razor-Component i've displayed the List of Razor-Component which is returend by the service.

@page "/"
@inject MyService myService


@CurrentFragment

@code{

  private RenderFragment CurrentFragment { get; set; }
  private List<TypeInfo> listOfRazorComponents;
 
  protected override void OnInitialized
  {
     listOfRazorComponents = new List<TypeInfo>(myService.GetRazorComponents());
     CreateFragment(listOfRazorComponents[0]);
  }

  RenderFragment CreateFragment(Type typeToDisplay) => builder =>
  {
     builder.OpenComponent(0, typeToDisplay);
     builder.CloseComponent();
  };
}

Now my stupid mistake... After i added the @inherits ExampleBase to all of my Razor-Components the Components wasnt reconized by my "MyService" because i checked there for

x=>x.BaseType is ComponentBase 

this caused an empty List of Razor-Components and when i called CreateFragment(Type typeToDisplay) the typeToDisplay was null.

I really dont understand why builder.OpenComponent(0, null) does not throw an NullReferenceException. Thats confusing to me

such a stupid error by my self took me a lot nerves... hope this will prevent others to forget this :)

Answer 2

For me it was just simple mistake in csproj setup. Instead of having my razor component having build action set to 'Content' it was set to 'None'. You can see that when you select file in project and RMB->Properties.

Not sure why it happened since I created razor file with 'Add->Razor component...' but I am sharing this with other people that may have the same problem.

Also, it was compiling fine so it caught me off guard