How do I find the packages that have Launch by Default set?

This seems to work for me:

/**
 * Get info on the preferred (launch by default) applications.
 * @return
 */
public String getPreferredAppInfo() {
    List<PackageInfo> packages = getPackageManager()
            .getInstalledPackages(0);
    List<IntentFilter> filters = new ArrayList<IntentFilter>();
    List<ComponentName> activities = new ArrayList<ComponentName>();
    String info = "";
    int nPref = 0, nFilters = 0, nActivities = 0;
    PackageInfo pkg = null;
    for (int i = 0; i < packages.size(); i++) {
        pkg = packages.get(i);
        nPref = getPackageManager().getPreferredActivities(filters,
                activities, pkg.packageName);
        nFilters = filters.size();
        nActivities = activities.size();
        if (nPref > 0 || nFilters > 0 || nActivities > 0) {
            // This is a launch by default package
            info += "\n" + pkg.packageName + "\n";
            for (IntentFilter filter : filters) {
                info += "IntentFilter:\n";
                for (int j = 0; j < filter.countActions(); j++) {
                    info += "    action: " + filter.getAction(j) + "\n";
                }
                for (int j = 0; j < filter.countCategories(); j++) {
                    info += "    category: " + filter.getCategory(j) + "\n";
                }
                for (int j = 0; j < filter.countDataTypes(); j++) {
                    info += "    type: " + filter.getDataType(j) + "\n";
                }
                for (int j = 0; j < filter.countDataAuthorities(); j++) {
                    info += "    data authority: "
                            + filter.getDataAuthority(j) + "\n";
                }
                for (int j = 0; j < filter.countDataPaths(); j++) {
                    info += "    data path: " + filter.getDataPath(j)
                            + "\n";
                }
                for (int j = 0; j < filter.countDataSchemes(); j++) {
                    info += "    data path: " + filter.getDataScheme(j)
                            + "\n";
                }
                // for (ComponentName activity : activities) {
                // info += "activity="
                // + activity.flattenToString() + "\n";
                // }
            }
        }
    }
    return info;
}

I was thrown by the fact that the return value for PackageManager.getPreferredActivities() seems to be zero instead of the total number of registered preferred activities. If it weren't always zero, checking for non-zero would be sufficient to see if a package has "launch by default" set. I also found PackageManager.getPreferredPackages() always returned zero for me. I also found passing null for PackageManager.getPreferredActivities() for the filters and activities (as mentioned in the Javadoc) gave a NullPointerException.