Activities vs Fragments for apps

Question

I have been trying to figure this out for a bit now. I see a lot of developers and youtubers (tutorials) saying that we should use as little activities as possible in order for a faster, more efficient and less resource heavy code/app. I was wondering if there is a way to create a Log-in and Sign-up using only the MainActivity for both Log-in and Sign-Up in combination with fragments for navigation between them.

Or

Do we need atleast 2 or more activities to handle that process ( Log-in & Sign-Up )?

Example: 1 activity for log-in and 1 activity for sign-up.

Appreciate and welcome any answers regarding this topic!

score 1 · Accepted Answer · answered Jun 09 '22 at 15:34

Theoretically, you could have your entire application run on a single Activity and use Fragments for all of the pages.

Each fragment has its own lifecycle within the activity.

MainActivity can look like this

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        loadFragment(2)
    }

    public fun loadFragment(page: Int){
        if(page == 1){
            // load login
            val manager = supportFragmentManager.beginTransaction()
            manager.replace(R.id.fragment_holder, LoginFragment()).commit()
        }else{
            // load register
            val manager = supportFragmentManager.beginTransaction()
            manager.replace(R.id.fragment_holder, LoginFragment()).commit()
        }
    }
}

LoginFragment can look like this

class LoginFragment : Fragment() {

    lateinit var myButton: Button

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        val view = inflater.inflate(R.layout.fragment_login, container, false)
        myButton = view.findViewById(R.id.my_button)

        myButton.apply {
            setOnClickListener { toRegister() }
        }
        return view;
    }

    fun toRegister(){
        // replace the fragment in main activity with register fragment
        (requireActivity() as MainActivity).loadFragment(1)
    }
}

RegisterFragment can look like this

class RegisterFragment : Fragment() {

    lateinit var mButton: Button
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        val view = inflater.inflate(R.layout.fragment_register, container, false)
        mButton = view.findViewById(R.id.my_button)
        mButton.apply {
            setOnClickListener { toLogin() }
        }
        return view;
    }

    fun toLogin(){
        // replacing the fragment in the main activity with the login fragment
        (requireActivity() as MainActivity).loadFragment(1)
    }
}

Basically, we replace the fragment displayed in the activity by calling loadfragment. This logic can be applied to as many fragments as is necessary.

What's the point of an Activity nowadays then, is it completely deprecated in favour of using Fragments? — Martin Melka, Jun 09 '22 at 15:39
It's dependent on the architecture that you choose to employ, for a simple application activities is the way to go, as its much easier to implement and manage. — Daniel Isaac, Jun 09 '22 at 15:56
So for more complex applications we should focus on the use of fragments more than activities then ? — Josef M, Jun 09 '22 at 16:15
You can choose either, you can have a complex application with Activities, or Fragments. None is significantly better than the other. For fragment based apps you can check out https://developer.android.com/guide/navigation/navigation-migrate — Daniel Isaac, Jun 10 '22 at 01:40
oh I see, that's interesting to know! It seems though that the general practice is, to use less activities and more fragments since its seems expensive to create/pause/destroy activities compared to fragments. Atleast since they introduced Jetpack! Found a similar topic on here as well, definately worth checking out! https://stackoverflow.com/questions/20306091/dilemma-when-to-use-fragments-vs-activities — Josef M, Jun 10 '22 at 07:48

Activities vs Fragments for apps

1 Answers1