7

NOTE: the actual question(s) is in the What my questions are section. The other sections are provided for giving better overview of the problem.

TASK

I want to decorate Android view using the Decorator design pattern. For my question I will be using decorating ViewPager as an example, but I believe the solution will be more general.

WHY DO I NEED IT

I want to be able to reuse different augmentations on the standard views in different solutions of mine. E.g. now I have timer-switching ViewPager and ViewPager that notifies me when the user reaches its end. With this solution I am aiming at adding auto-switching notifying ViewPager (i.e. combining both my current extensions) in my next solution a one-liner. Decorator pattern is exactly for that.

WHAT MY CURRENT APPROACH IS

  • I already wrapped the targeted ViewPager in ViewPagerDecorator

  • I also did the desired extensions of the decorator - AutoSwitchViewPager and NotifyOutOfBoundsViewPager (based on this). Now I can even do

    new AutoSwitchViewPager(new NotifyOutOfBoundsViewPager(viewPager)).

  • Now I am trying to figure out how to place this run-time created view in the layout. I am currently trying to figure out if I can replace ordinary ViewPager from layout propagating its xml attributes to the decorated view.

WHAT MY QUESTIONS ARE

  • Is there a way to copy over the xml attributes from a layout-defined view to runtime constructed one (LayoutParameters at least)
  • An alternative would be to use ViewStub, but I did not find a way to inflate ViewStub with something completely run-time constructed (without using xml Layout). Is there such a way?

WHAT HAVE I READ

I have stumbled upon these related resources:

  • Decorating Android views - this is not entirely decorating the views in the sense that the decorator would not subscribe to the different events of the view. The decoration needs to be triggered by a special trigger method. However, the decorations I aim for truly need to act as full extensions of the decorated class.
  • Decorator pattern Android - Here the decoration is again triggered via special method
  • Decorating an Android activity - with all the respect I have for ComonsWare I am very far away from questioning his statement. On the other hand, I believe that the views in Android allow you for more runtime modifications than the activities, so I still my case is plausible.
Community
  • 1
  • 1
Boris Strandjev
  • 46,145
  • 15
  • 108
  • 135
  • 2
    read about LayoutImflater.setFactory/LayoutImflater.setFactory2 – pskink Nov 06 '14 at 08:35
  • LayoutInflater.Factory2 is better as it provides additional `View parent` parameter but it requires API 11+ – pskink Nov 06 '14 at 10:22
  • just forgot to add that when implementing LayoutInflater.Factory2 in your Activity make sure you call super implementation – pskink Nov 06 '14 at 17:11
  • @pskink thanks for all the comments I am currently exploring this new possibility you pointed me to. Thanks you for giving me a direction! – Boris Strandjev Nov 06 '14 at 17:18

1 Answers1

6

After weeks of struggle and applying few different design approaches I think that I finally got the solution! As the solution is not as easy to explain as to fit in SO post I created a blog post to explain all my struggles. I also accompany my explanations with source code to demonstrate my ideas available here.

Boris Strandjev
  • 46,145
  • 15
  • 108
  • 135
  • 1
    Is your solution still current in Material Design's ViewPager two years later? – IgorGanapolsky Mar 15 '16 at 13:25
  • 1
    @IgorGanapolsky If you are asking me whether the `ViewPager`'s new concepts are incorporated in the source code I provide - I believe it is rather not. However, the purpose of the question and the answer as well is to present rather a general approach, than particular `ViewPager` bound solution, though the latter is used as POC. – Boris Strandjev Mar 15 '16 at 14:41
  • 2
    hi @BorisStrandjev I know it's an old question and you've probably moved on, but I've stumbled on your question and wanted to show that me n my team developed an annotation based java code generation library to remove the boilerplate from applying the decorator pattern. If you're interested you should check it out https://github.com/eyeem/decorator – Budius Apr 05 '16 at 16:10