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or "How to decouple UI from business logic in Delphi?"

Each target platform has its own set of native firemonkey controls (Windows=VCL, MacOS=TMS mCL, Android=D.P.F, iOS=TMS iCL and D.P.F). The new FireUI (multi-device form designer) is a great solution for styled components, but not for native components because it still requires the same component on the master pane to support all platforms. As you cannot mix them on the same form, it completely breaks the whole idea with Delphi.

A lot of developers would say that Delphi is the broken approach, see "Why FireMonkey is so fundamentally wrong in every aspect". However, the premise for this question is NOT to argue against Delphi, but to get the best results out of what it does offer.

The conclusion is then that for each form in your application you have to make a separate form for each target platform. This leads to these questions:

Challenge 1: How to include different form files in your project depending on your target platform?

Solution 1: include all of them, i.e. MainForm_IOS.pas, MainForm_Android.pas, MainForm_Win, MainForm_OSX.pas, and then use compiler directives inside the files, so only the content of one of the files is active. Disadvantage: a large application can have many forms (we have around 40), so we are talking about a large number of included files.

Solution 2: Do not include them in the project, but instead just place them in seperate folders. Then you can add the matching folder to the search path for each target platform. Disadvantage: They will not show up in the Project Manager, so it will slow down the workflow every time you need to find a file.

Solution 3: Create a project for each target platform. Disadvantage: Every time you add new units or change common project settings you have to (remember to) apply it to all projects.

Update: As suggested in the Malcom Groves video, placing all the business logic in a package will remove the disadvantage from Solution 3. So I consider solution 3 as the best approach.

Challenge 2: How to connect the different device forms to the (same) business logic?

Possible solution: Create a "Helper" class that contains all the code you would normally have in the form unit.

Update: This "Helper class" is actually what the MVVM calls a ViewModel. What I need seem to be a MVVM framework that can support the databinding. I have made another question about that.

Any input and suggestions about best practice are welcome.

Community
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Hans
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    I would make a project for each OS and have a layered approach, the forms are the presentation layer and are unique for each OS. All the rest is business layer (which can be further layered down, depending on your needs). – whosrdaddy Dec 08 '14 at 09:20
  • @whosrdaddy: Great, I just added that as a 3rd solution to Challenge 1. – Hans Dec 08 '14 at 09:28
  • About challenge 2, I would apply an MVC pattern. Anyway this question is not fit for SO as this question is primarily opinion based ;) – whosrdaddy Dec 08 '14 at 09:31
  • I fully agree with whosrdaddy - this question is not fit for SO, especially how you prelude your real questions. – iamjoosy Dec 08 '14 at 09:36
  • There are several theoretical design patterns, but my question is hands-on. How to actually separate UI from business logic in Delphi? – Hans Dec 08 '14 at 09:37
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    Hans, look e.g. here [MVVM](https://www.youtube.com/watch?v=Ci1HP8ZBJxk) – iamjoosy Dec 08 '14 at 09:40
  • @iamjoosy: This question might be on the edge of SO, but where else could this kind of question be asked? – Hans Dec 08 '14 at 13:57

1 Answers1

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For challenge 1: You can conditionally link in your FireMonkey form resources depending on the compile target:

{$R *.Windows.fmx MSWINDOWS}
{$R *.Macintosh.fmx _MACOS}

etc.

This is excatly what the XE7 Multiview designer does, but I see nothing against using this mechanism to link whole form files conditionally in to your executable. Of course you might also want to ifdef the corresponding units in your project file.

For challenge 2: Just use some form of Model View Controler logic. So your platform dependant forms will talk to a platform independant controler.

iamjoosy
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  • Challenge 1: Do you mean linking in the form units? - I suppose that corresponds to solution 2? Challenge 2: I agree and my question is about how to actually implement that with Delphi. – Hans Dec 08 '14 at 09:46
  • @Hans just look at my comment in your question. Or just google for Delphi MVC / MVVM – iamjoosy Dec 08 '14 at 09:58