How to create an ArrayList that is accessible by different classes in android?

Question

I got a CameraView class (with an onPreviewFrame) which on each incoming frame calculates a value of 1 or 0 depends on the frame brightness, I want that on each incoming frame the calculated value will be add to an ArrayList. The problem begins when I need to read the data that is in the ArrayList from my MainActivity class.

How do I create a list that different class can get to?

I know it's relatively simple but i'm new to java/android and trying to wrap my head around how it all works.

So you want to be able to send an Arraylist from one class to another, right? What editor are you using? — Trey50Daniel, Mar 17 '16 at 19:27
@Trey50Daniel ye that's basically it, and i'm using Android Studio. — Voly, Mar 17 '16 at 19:35

score 0 · Answer 1 · answered Mar 17 '16 at 19:39

Here is an example of what I recently used when I needed to send a HashMap from one activity to another:

Intent i = new Intent(getApplicationContext(), BillPage.class);
i.putExtra("workPriceMap", (HashMap<String, Float>)workPriceMap);
startActivity(i);

And then in my other class I used this:

private Map<String, Float> workPriceMap;
workPriceMap=(HashMap<String,Float>intent.getSerializableExtra("workPriceMap");

score 0 · Answer 2 · edited May 01 '22 at 03:55

You can create a singleton class, like below:

public class Singleton {
    
    private static Singleton instance;
    
    private List<String> frameList;
    
    private Singleton() {
        this.frameList = new ArrayList<String>();
    }
    
    public static Singleton getInstance() {
        if(instance == null)
            instance = new Singleton();
            
        return instance;
    }

    public List<String> getList() {
        return this.frameList;
    }
    
    public void setList(List<String> frameList) {
        this.frameList = frameList;
    }
    
}

You can then access it from any class by:

Singleton.getInstance().getList().add("x");

This is better than having a static List at least. – Trey50Daniel Mar 17 '16 at 19:46 — Trey50Daniel, Mar 17 '16 at 19:46

score 0 · Answer 3 · answered Mar 17 '16 at 19:50

You could use a singleton method, this way you can have the same reference everywhere.

public  class YourClass {

    private ArrayList<String> yourList;
    private  YourClass instance;

    private YourClass(){
        yourList = new ArrayList<>();

    }
    public static YourClass getInstance(){
        if(instance == null){
            instance = new YourClass(); 
        }
        return instance;
    }

    public ArrayList<String> getYourList(){
        return this.yourList;
    }

} 

public class OtherClass{
    public static void main(String [] args){
        ArrayList<String> yourList  =  YourClass.getInstance().getYourList();
    }
}

How to create an ArrayList that is accessible by different classes in android?

3 Answers3