wpviews: gallery shortcodes displaying "undefined" for an instant

[iseulde]

We should return ''; while loading the gallery.
But ideally, we should create a loading function that inserts some content, because doing an ajax call to render a view is not uncommon. The embed view does the same... Something like this.loading() maybe?

[iseulde]

This will make sure getHtml actually returns something.

[azaozz]

How about we insert a temporary (loading) placeholder while the data is being fetched? We can style it any way we want depending on the view, hide it completely, etc.

[helen]

I thought we had discussed a loading indicator at some point - we should probably do that.

[azaozz]

Replying to helen:

I thought we had discussed a loading indicator at some point

Right. In 28761.3.patch:

• Add loadingPlaceholder() that returns the html. Would it be better if this was a template?
• Fix setContent(), it should empty the element before appending the new node.
• getHtml() should always return a string.

The default loadingPlaceholder has the dashicons-admin-media icon and a small "loading" CSS animation. Does it need to be more "distinct" or more styling? (To test it: edit line 50 in mce-view.js, from var html = this.getHtml() || this.loadingPlaceholder(); to var html = this.loadingPlaceholder();.)

[azaozz]

In 29019:

TinyMCE wpView:

• Add loadingPlaceholder() that returns some html to use as placeholder while the view is loading. Includes a subtle CSS based loading animation.
• Fix setContent(), it should empty the element before appending the new node.
• Change getHtml() to always return a string.

Fixes #28761.