Reflection- viewpager not working after the application of reflection

I am trying to use reflection in my app. i have created one common method which hits the API on request of different classes.

try {
                Class classname = Class.forName(componentName);
                Object classobject = classname.newInstance();
                Method method = classname.getMethod("responseString", String.class);
                method.invoke(classobject, response);
            } catch (Exception e) {
                e.printStackTrace();
            }

When i use this the viewpager in the class gives a NPE at this line

 viewPager = (ViewPager) findViewById(R.id.pager_dashboard);

If i don't use reflection then this is working. What could be the problem?