1) Don't subclass Activity for classes that do not display anything. Activity (and any subclasses) is designed to be a visual class.
2) Create your own class with a constructor that takes a Context instance and use that instance to get the shared preferences object. I have code like this in one of my Receiver classes (which is also non-visual): SharedPreferences prefMgr = PreferenceManager.getDefaultSharedPreferences(context); ---------------------------------------------------------------------- There are only 10 types of people in the world... Those who know binary and those who don't. ---------------------------------------------------------------------- On Sat, Dec 12, 2009 at 4:28 PM, DrLaban <[email protected]> wrote: > Hi! > > I'm a beginner at Android but have coded a bit of Java before. > > I'm trying to figure out how I'm supposed to instantiate and use a > class that does not contain any visual elements, but holds a lot of > functions for processing data. > My main activity, on either a button click or by pressing the back- > button, shall call functions in another class, which is void of visual > elements, that takes care of data processing. > I like to keep my classes logically separated and this non-visual > class can and will be used by other classes later throughout the > application. > > I have hit a few speed bumps on the road and I now need some help. I > have two issues; > > Preface: > I have two classes. One called "textfields" that contains a view of a > bunch of textfields and a button. This is an Activity-class. > I also have a non-visual class "logic" that contains all the functions > I need for logic handling of data and values. This is, in my mind, a > non-Activity based class (though I might be wrong). > These classes use getSharedPreferences to store and fetch values from > time to time. I am also going to extend my application to make real > good use of the stored values, but I need to start somewhere. :) > > 1: > Now, for instance, in my Activity "textfields" I instantiate my visual- > less class called "logic" at the onCreate() event. > When the onPause() event fires in "textfields", I call a function in > the "logic"-class. > The "logic" class reads values stored in getSharedPreferences. Here, I > get a NullPointerException when executing getSharedPreferences within > the "logic"-class. I'm extending the "logic"-class with Activity, in > order to be able to use the getSharedPreferences-function at all. Why > am I getting a NullPointerException and how should I solve the > problem? > > 2: > I have no constructor in the "logic"-class as it has been stated on a > few occasions that we instead should use onCreate(), onResume(), etc. > I can't figure out when any of these events fire when I'm not using a > class containing an Activity. I have tried to override and use super > to chain the events, but nothing I do calls either onCreate, onResume > or whichever event when I from "textfields" instantiate "logic". > "Logic" doesn't seem to be running onCreate() or onResume() as a class > 'usually' does. When I want to use a non-visual class, what is the > better way of doing this? I also need access to getSharedPreferences. > > Thank you for your time, I'm appreciating any help I can get. > > -- > You received this message because you are subscribed to the Google > Groups "Android Beginners" group. > To post to this group, send email to [email protected] > To unsubscribe from this group, send email to > [email protected]<android-beginners%[email protected]> > For more options, visit this group at > http://groups.google.com/group/android-beginners?hl=en -- You received this message because you are subscribed to the Google Groups "Android Beginners" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/android-beginners?hl=en
