Weakreference get null in async task

Question

I use Weakreferences for the callback in a asynctask. In the constructor of the asynctask i give a list with references. In my situation the list contains 3 references, 2 fragment references and 1 java class reference.

When i check the list which is recieved by the constructor of the asynctask the list contains the 3 (filled) references. I copy these to a local list (in the asynctask). When i check this list this has also the 3 (filled) references.

Then the asynctask is (doInBackground) is executed which don't touch the references. When i check the references with a breakpoint at the first line in the doInBackground method the 3th (java class) reference is null. The other 2 references are still filled.

Everything worked fine till tomorrow. I checked the differences in code but there are no big differences. I tryed to roll them back with no result. Has someone an explaination for this?

I created the references on this way: WeakReference<e_Alerts> wr = new WeakReference<e_Alerts>(this); callbackReferences.add(new WeakReference<>((e_Alerts)tab_AlertListOverviewFragment)); callbackReferences.add(new WeakReference<>((e_Alerts)tab_AlertMapsOverviewFragment));

And the list i used is a simple List<WeakReference<e_Alerts>> callbackReferences; list.

--------------------------------------------------------Update--------------------------------------------------------

doInBackground code:

    try {
        //Downloads the alert XMLs from the internet and parses it to xmlAlerts
        this.alerts = new XmlDownloader().DownloadAlerts(inputUrl);
        // Filters the xml alerts so only the alerts where the enduser is interessed in will remain
        this.alerts = filterAlerts(this.alerts);
        // Converts the remaining xmlAlerts to Alerts;
        this.result = new AlertConverter().Convert(this.alerts);
    }catch (Exception e) {
        Log.e("At_allAlerts",e.getMessage());
    }
    return null;

filterAlerts Method:

private List<Item> filterAlerts(List<Item> alerts) {
    List<Item> filteredXmlAlerts = new ArrayList<>();

    for (Item alert : alerts)
    {
        Location alertLocation = new Location("");
        alertLocation.setLatitude(alert.getGeometries().get(0).getLocations().get(0).getLat());
        alertLocation.setLongitude(alert.getGeometries().get(0).getLocations().get(0).getLng());

        for(Area area : this.areas)
        {
            if (area.IsOrganization() && alert.getCountryCode().toLowerCase().equals(area.getOrganizationcode().toLowerCase())){
                filteredXmlAlerts.add(alert);
                break;
            }
            else if(!area.IsOrganization() && isAlertInRegion(alertLocation, area)) {
                filteredXmlAlerts.add(alert);
                break;
            }
        }
    }
    return filteredXmlAlerts;
}

The XmlDownloader: Downloads an xml feed an parses the xml to objects with a library

The AlertConverter: converts the xml object to the object i use in my app

Both classes can work without the asynctask class and don't use the references.

post the code of the DoInBackgriound... we nned to see if the list is getting manipulated in other methods... — ΦXocę 웃 Пepeúpa ツ, Mar 30 '16 at 11:23

score 1 · Answer 1 · answered Mar 30 '16 at 12:13

1

The garbage collector can free/null objects without a "strong" reference. It can be the case that the variables that you use doesn't have any references left

answered Mar 30 '16 at 12:13

Mike Holtkamp

94
8

Thanks for your answer but for some weird reason the problem is solved by himself. I removed the app manually from my phone (for testing first initialization) and since this moment everything works fine again. I checked the changes (in history) with the clases at the moment from this post so i can find a explaination why it was broken and fixed again but there are 0.0 changes....... I don't understand it but it works so i'am happy :-D – CodeNinja Mar 30 '16 at 12:45
I found something more... the problem is not "magically gone".... When i start the app the first time the gps location is asked to an gpsManager class by the alert manager. When i disable that the app gets the gps location `(if gpsEnabled){gpsManager.getGps();}` the gps class (with a Location listener) then the Alertmanager reference goes to null else not..... – CodeNinja Mar 31 '16 at 07:35

Weakreference get null in async task

1 Answers1