My issue is I am not sure how to implement on this page the same filtering and search function as on the other page. On the parent view it says "Only Views listing posts can have custom search inputs."
Okay I understand you would like to filter the view of posts by text search and by taxonomy term (from an alphabetical grouping taxonomy), but that View of posts is nested inside another taxonomy View for grouping purposes. Unfortunately there is no simple solution in this scenario, because, as the message explains, it is not possible to add front-end filtering to taxonomy Views or User Views. Only Views showing posts of some kind support front-end custom search filters. Furthermore, if you add front-end filtering controls to the inner nested View, by default you will produce a list of results grouped alphabetically, with search filters repeated in each grouped set of results. That is not really ideal for what you want to achieve.
You could try a workaround here, but it's not really intended to use Views this way so I cannot guarantee it will work exactly as expected. I think it will be worth the effort to test, though. You could try adding custom search filters to the View of posts, then try displaying the filters separately from the results of that View. We offer shortcodes for displaying the filters and results independently. Use the following shortcode syntax to display only the results part of the nested View, not the filters, nested inside the loop of your existing taxonomy View:
[wpv-view name="your-nested-view-slug" view_display="layout"]
Replace your-nested-view-slug with the slug or name of the post View. Add any other shortcode attributes here from your current View setup, if needed for filtering or other purposes. To display the search filters section independently, use the wpv-form-view shortcode instead with this format:
[wpv-form-view name="your-nested-view-slug" target_id="self"]
Again, replace your-nested-view-slug. You should not add any other shortcode arguments.
https://toolset.com/documentation/programmer-reference/views/views-shortcodes/#wpv-view
https://toolset.com/documentation/programmer-reference/views/views-shortcodes/#vf-1496531
The limitations I expect, and you should be aware of:
- AJAX updates are not supported for either View. Searching and filtering must trigger full page reloads, and your View must update the URL to include URL parameters when searching.
- Pagination is not well supported in this scenario. If you add pagination to the inner View for example, pagination will appear for each group of results. If you add pagination to the outer View, the number of posts per page will not be predictable because you're actually paginating based on the term groups, not based on the posts.
- You may need to adjust the outer taxonomy View's Query Filter to respond to the same URL parameter used by the inner View's Query Filter. Otherwise you may see empty term groups after filtering.
