code: public static void convertActivityToTranslucentBeforeL(Activity activity) {
          try {
              Class<?>[] classes = Activity.class.getDeclaredClasses();
              Class<?> translucentConversionListenerClazz = null;
              for (Class clazz : classes) {
                  if (clazz.getSimpleName().contains("TranslucentConversionListener")) {
                      translucentConversionListenerClazz = clazz;
                  }
              }
              Method method = Activity.class.getDeclaredMethod("convertToTranslucent",
                      translucentConversionListenerClazz);
              method.setAccessible(true);
              method.invoke(activity, new Object[] {
                  null
              });
          } catch (Throwable t) {
          }
      }
docs: Calling the convertToTranslucent method on platforms before Android 5.0