WebComponents Forms InputFile - Change the _inputFileElement field to protected so a class can be derived from InputFile

[Valks]

Hi,
I'm wondering if it's possible to have the InputFile.cs line 20 changed to protected instead of private so that it can be used in a derived class which replaces the BuildRenderTree().

aspnetcore/src/Components/Web/src/Forms/InputFile.cs

Line 20 in e14e5bc

private ElementReference _inputFileElement;

The reason this change is necessary is that the elementReference needs to be set during the BuildRenderTree() call for the component to work.

aspnetcore/src/Components/Web/src/Forms/InputFile.cs

Line 66 in e14e5bc

builder.AddElementReferenceCapture(3, elementReference => _inputFileElement = elementReference);

I'm happy to submit a PR with the change, just wondering if there's any concerns I'm not aware of?

[mkArtakMSFT]

Thanks for contacting us.
Please share more details about your scenario. We would like to understand how it's going to be used.

[Valks]

Sure, I'm looking to change the BuildRenderTree because I'm working with web components (in my case the fast.design framework) and I'm overloading all the form components to use the fast.design web components.

Now the fast framework doesn't have a customization for <input type="file"> yet, but this problem will also affect other web component frameworks i.e.
https://www.webcomponents.org/element/@fluidnext-polymer/paper-input-file

The reason I want to derive from the InputFile component is to take advantage of the work already done to handle files. A lot of those classes related to the javascript interop are internal and I don't need access so long as I can assign the ElementReference.

The easiest way to do what I need is to either expose the _inputFileElement by making it protected or add a helper function to call builder.AddElementReferenceCapture(3, elementReference => _inputFileElement = elementReference);. Personally I feel making _inputFileElement protected achieves the desired outcome with minimal impact and doesn't expose it to users of the new component. Especially considering it's already a public API.

For example, currently BuildRenderTree looks like:

aspnetcore/src/Components/Web/src/Forms/InputFile.cs

Lines 60 to 68 in e14e5bc

	/// <inheritdoc/>
	protected override void BuildRenderTree(RenderTreeBuilder builder)
	{
	builder.OpenElement(0, "input");
	builder.AddMultipleAttributes(1, AdditionalAttributes);
	builder.AddAttribute(2, "type", "file");
	builder.AddElementReferenceCapture(3, elementReference => _inputFileElement = elementReference);
	builder.CloseElement();
	}

I'd want to change it to something like

        /// <inheritdoc/>
        protected override void BuildRenderTree(RenderTreeBuilder builder)
        {
            throw new NotImplementedException("Waiting on feedback to issue: https://github.com/dotnet/aspnetcore/issues/28533");
            builder.OpenElement(0, "fast-input");
            builder.AddMultipleAttributes(1, AdditionalAttributes);
            builder.AddAttribute(2, "type", "file");
            builder.AddElementReferenceCapture(3, elementReference => base._inputFileElement = elementReference);
            builder.CloseElement();
        }

Or for the paper-input-file

            builder.OpenElement(0, "paper-input-file");

[SteveSandersonMS]

Understood. Thanks for clarifying!

We're thinking of extending #24899 to include the functionality you're asking for (that is, making the field writable via a protected setter). I'll add a note there.

[SteveSandersonMS]

Done in #29555