Older Android system doesn't have the method call addDexPath.And it's not safe to get current data dir from classloader

[qtiuto]

A solution for the first is to set the dexElements field of the dexPathList Field in the BaseDexClassLoader.class,It's ok after api 4.
And a better solution for the second is to invoke the static method currentPackageName() in ActivityThread.class. Here's the code:

private static String getPackageName(){
        try {
            if(sCurrentPackageName==null) sCurrentPackageName=Class.forName("android.app.ActivityThread").
                    getDeclaredMethod("currentPackageName");
            if (Build.VERSION.SDK_INT>=18||Looper.getMainLooper()==Looper.myLooper())
                return String.valueOf(sCurrentPackageName.invoke(null));
            else {
                final String[] ret=new String[1];
                Handler handler=new Handler(Looper.getMainLooper(), new Handler.Callback() {
                    @Override
                    public boolean handleMessage(Message msg) {
                        try {
                            ret[0]= (String) sCurrentPackageName.invoke(null);
                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                        synchronized (ret){
                            ret.notify();
                        }
                        return true;
                    }
                });
                handler.sendEmptyMessage(0);
                synchronized (ret){
                    ret.wait();
                }
                return ret[0];
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return "";
    }