Threads...

1. class MyThread extends Thread {
2.   //Necessary data
3.   boolean active;
   
4.  
5.   MyThread() {
6.     //Constructor
7.     active = false;
   
8.   }
9.  
10.   void start() {
11.     super.start();
12.   }
13.  
14.   void run() {
15.     while(true) {
16.       if(active) {
17.         //Perform loading
    
18.         active = false;
19.       }
20.     }
21.   }
    
22.  
    
23.   void trigger() {
24.     active = true;
25.   }
26.  
    
27.   boolean done() {
28.     return !active;
    
29.   }
    
30. }

After initialization and a call to start(), trigger() will start the loading, done() will return true if done loading. Insert necessary loading where it says "//Perform loading".

I'm not sure if this will help you entirely, I am not exactly sure how you will have to modify it to suit your needs... But I thought I would provide it so that you can use it if necessary.

Ok thanks to you i've moved a step forward.

No need for a callback, the thread can set a flag which can be polled to see if the task is completed.