Is it more useful for the English learners to study grammar first accordingly then comprehension or study grammar through text?

I agree with Mr Haider. Grammar should be studied and taught separately. Task-based lessons are nothing but beating around the bush.

Well, there are different tendencies in the philosophy of teaching ESL. I will take a shortcut and give you my personal viewpoint on the matter. I think that grammar should be studied separately because I think that grammar is more like the scientific face of the language. Grammar is not a language skill and its effect on the process of comprehending a language is minimal. I am not undermining the importance of grammar but I am only saying that you should study it separately and then incorporate it into your language as it refines your lingual product.