Hi Bob, On Wed, Nov 13, 2019 at 9:59 AM Bob Miller via 4D_Tech <[email protected]> wrote:
> The example in the docs doesn't help me understand what you mean about > using Form with a listbox. > Can you step through a little example of how Form would help in this case, > to control a listbox? > Happy to try to help. I recently posted a suggestion for replacing a pretty complex list form, not a listbox, with a listbox and detail subform. It even has a picture. https://forums.4d.com/Post/FR/32395457/1/32403208#32403208 I got a lot of useful ideas from the blog: https://blog.4d.com/display-an-entity-selection-in-a-list-box/ https://blog.4d.com/display-a-collection-in-a-listbox/ A couple of tips I'll pass along that have emerged as being really helpful for me: - Think about whatever is in the listbox in terms of the actual data - not in terms of rows and columns. When you want to select or edit something you do it in the data and the listbox displays the results. This is almost completely opposite the way you have done it for years. - Whatever you are going to display in the listbox if you want to query, hide, select some of the elements create two references to the data (collection or entity selection). Something like: Form.sourceCollection // this is the actual data Form.listboxDisplay // this is what's displayed in the listbox You set it up initially by assigning the source to the display: Form.listboxDisplay:=Form.sourceCollection Why is this a useful? Let's say I have a big list of names and I include a search widget. I want to have the listbox show only the elements that match the search condition. The collection.query() is wonderfully easy. It returns either a collection (if you query a collection) or an entity selection (if you query that). So Form.listboxDisplay:=Form.sourceCollection.query(" name = :1 "; Get edited text) puts the result of the query in the listbox. But this is memory inefficient - you may think. It's not because Form.sourceCollection and Form.listboxDisplay are references to the data. Totally different from arrays or selections. Creating multiple references doesn't significantly increase the memory usage. BTW - if you allow the user to make changes in the listbox using this scheme because you are using a reference the changes in the listbox 'flow' through to the sourceCollection. If you using an entity selection the changes are made to the entity. The bottom line is Form and ORDA represent a fundamentally different approach to presenting data to the user. It's worth spending the time to learn it. I can do things now with a few lines of code that used to require multiple methods and dozens (hundreds) of lines of code to accomplish the same effect. -- Kirk Brooks San Francisco, CA ======================= What can be said, can be said clearly, and what you can’t say, you should shut up about *Wittgenstein and the Computer * ********************************************************************** 4D Internet Users Group (4D iNUG) Archive: http://lists.4d.com/archives.html Options: https://lists.4d.com/mailman/options/4d_tech Unsub: mailto:[email protected] **********************************************************************
