Question

I need to find a solution that holds and accesses large chunks of complex global data and methods. It has to be accessible from within activities and normal instance variables of various data classes.

This is how I have done it. I would just like to know if there is anything wrong with it or if there is a better/cleaner way.

First I extend Application like recommended many times…

public class MainDataManager extends Application{

   public ... large chunks of data in arrays, lists, sets,....

   //static variable for singleton access from within instance variables of other classes
   public static MainDataManager mainDataManager;

  //create and init the global data, and store it in the static variable of the class
  @Override
      public void onCreate() {
        super.onCreate();
        //in case it should get called more than once for any reason
        if (mainDataManager == null) {
            init();
            mainDataManager = this;
            }
      }

Now accessing it from within activities like everywhere recommended…

MainDataManager mainDataManager = (MainDataManager)getApplicationContext();

And since I need to access it from normal instances of data classes …

public class MyDataClass {
    public MainDataManager mainDataManager;
    public String name;

    public MyDataClass(String namex) {
        this.name = namex;
        //this is why I defined the static variable within MainDataManager, so
        //one has access to it from within the instance of MyDataClass
        this.mainDataManager = MainDataManager.mainDataManager;
    }

      public void examplesForAccessing() {
      //some examples on how to access the global data structure and associated methods
        mainDataManager.someMethodAccess();
        xyz = mainDataManager.someDataAccess;
        mainDataManager.someIndirectMethodAccess.clear();
        mainDataManager.someOtherData = false;
    }
}

Since I have not done this so far, I would like to know if there is anything wrong with this. Memory, efficiency, …

Thanks very much!

May I add a little sidenote?
I could also have just used a class MainDataClass and access by MainDataClass.var or MainDataClass.method(). Is there any REAL disadvantage?

Is the data in both cases held in heap/stack?

Answer 1

You haven’t given much detail about your “large chunks of data” but keep in mind that the onCreate method is the first things that runs when your application is starting and it runs on the main/UI thread. This means that if you do long tasks in your init() method your UX will be poor, not to mention that you are risking an ANR exception.

The solution for that is simple:

1. Keep your onCreate short
2. Create a BG thread and use it to run all initialization code
3. Show a “Splash”/”Welcome” screen with the a proper progressbar while the BG thread is running.