Blazor posibility to wait for OnInitAsync before initial rendering

[isc30]

This is somehow related to #9190.

When using prerendering, the full page is rendered (with all the components rendered after OnInitAsync). When the client side loads, it will not wait for OnInitAsync before the initial render, making the page "pop-in" for some content that was already there.

Rendering before OnInitAsync has finished is a great idea for implementing "loading" screens, but it doesn't play well with the initial render.

Is there any way to avoid that "pop-in" effect by disabling the initial render before OnInitAsync for all components on demand?
If not, how could it be implemented?
Thanks

[javiercn]

@isc30 thanks for contacting us.

You can cache the data during the prerendering phase and load it synchronously after that. If you do it that way there is no async code path and you don't get the "pop-in"

[isc30]

Hi @javiercn, in this specific case I need to fetch some json from an endpoint, but I don't want to "ruin" the prerendered page by having a "loading" message for 100ms. There is no way to just "keep" what's in the page until I got every component fully initialized. I would prefer to not cache anything.

That's why i was suggesting introducing a method/flag in the WebAssemblyHost to defer the render after every component's OnInitAsync has finished.

The idea is to make it consistent with prerendering behavior so the initial output is as similar as possible

[mkArtakMSFT]

We've moved this issue to the Backlog milestone. This means that it is not going to happen for the coming release. We will reassess the backlog following the current release and consider this item at that time. However, keep in mind that there are many other high priority features with which it will be competing for resources.

[isc30]

Hi, this could be considered a bug. Imagine the following scenario:

public class MyComponent : ComponentBase
{
    protected override bool ShouldRender() => false;
}

This will trigger the initial render either way, completely ignoring the flag.
Please consider this minimal change before the main release, since it opens the possibility to create custom hydraters for prerendered content.

[javiercn]

@isc30 I'm not sure what you are asking us to do,

but changing something on ComponentBase is not possible for us until/after the 5.0 release. This is part of the component model so it can't only be applied to Blazor WebAssembly and it is not an area where we plan to make changes.

We'll look into documenting the pattern to follow here in the future.

[isc30]

Similar fix from #22202 would solve this too