How to render a ViewComponent conditionally depending on its content?

[akarzim]

I tired to figure out how to render a ViewComponent or not according to its content 🤔

My use case is:

 class DefinitionEntryComponent < ViewComponent::Base
    def initialize(term:, description: nil)
      @term = term
      @description = description
    end

    def call
      # do something
    end

    private

    attr_reader :term

    def description
      @description || content
    end
  end
end

Here, my description is either the one given at initialisation, or the block content of my component.

What I want to achieve is to render my component only if the actual description is not null. My first approach was to implement the #render? method like this:

    def render?
      !description.nil?
    end

This sounds great. But the #render? method arrives too early in the ViewComponent lifecycle, and content has not been evaluated by the time the method is called 😢

Workaround

What I discovered by digging into the ViewComponent::Base class and the documentation is that the #render? method is actually called twice in the lifecycle. Here's a workaround that takes advantage of this:

    def render?
      return true unless defined?(@__vc_content_evaluated)

      !description.nil?
    end

I'd be happy to use the #content_evaluated? method, but I only need the first part of the conditional.

view_component/lib/view_component/base.rb

Lines 326 to 328 in cdd934c

	def content_evaluated?
	defined?(@__vc_content_evaluated) && @__vc_content_evaluated
	end

Question

Do you know a better way of achieving my goal without using the instance variables of the ViewComponent::Base class?

[joelhawksley]

I was unable to validate this issue, even by copying your provided component into the test suite: #2343. I'm going to close this as outdated but please reopen as an issue if this is still a problem for you ❤️