通用 Razor 类型参数作为变量传递

Question

Razor/Blazor component with Generic Type Parameter as a variable

 <QueryRow  Titem="Person"/>

Works

in the above component i can recieve the parameter

 Type typeParameterType = typeof(Titem);

and create an instance

 object? myObject = Activator.CreateInstance(typeParameterType);

That all works great, however

  public Type mytype = typeof(Person);

  <QueryRow  Titem="@mytype"/>

Does not work, I need be able to pass the types down from the parent as list of types or strings I can convert to real types using reflection.

How do I pass the type parameter as a variable such as

mytype = typeof(Person);

I can do all this in code but not in razor!!! what am I doing different/ wrong ?

for example, Person starts as a string below

   Type? typeArgument = Type.GetType("Person");
   Type genericClass = typeof(QueryRow<>);
   Type constructedClass = genericClass.MakeGenericType(typeArgument);
   object? createdType = Activator.CreateInstance(constructedClass);

works great, but then I have to use blazor's Dynamic component as a workaround to do the render, which I'd rather avoid as it seems a bit yuk

Answer 1

You can't use a variable as the type parameter in this way.

You can create a RenderFragment using a bit of reflection:

public Type myType = typeof(Person);

@MakeQueryComponent(myType)

@code {
    RenderFragment MakeQueryComponent(Type typeParam)
    {
        var genericType = typeof(QueryRow<>)
            .MakeGenericType(new[] { typeParam });

        RenderFragment frag = new RenderFragment(b =>
        {
            b.OpenComponent(1, genericType);
            b.CloseComponent();
        });

        return frag;
    }
}

UPDATE

Following GitHub issue 26781 , the Blazor team have now encapsulated the above method of generating a RenderFragment into a new component called DynamicComponent.

See source code and guidance .