Using a coroutine without a "GlobalScope" in Activity and Fragment

ActivityとFragmentでGlobalScopeを使わないでコルーチンを利用する方法です。
GlobalScopeを何気なく使わないようにしましょう。

Do not use GlobalScope in local scope

At First. Look at follow code.
This example code is wrong coroutine usage.

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        setSupportActionBar(toolbar)

        GlobalScope.launch { 
            val data = withContext(Dispatchers.IO) {
                loadData()
            }
            initUi(data)
        }
    }
    ...
}

This is a bad way.
But Why?
According to Officially GlobalScope explains at "GlobalScope - kotlinx-coroutines-core", GlobalScope's lifecycle scope is Process-Level. So, this loading data may keep running after Activity(also Fragment) Destroyed, and then happen unexpected behavior.

How to use Coroutines on Activity and Fragment without GlobalScope : Use LifecycleScope

Use androidx.lifecycle:lifecycle-runtime-ktx:2.2.0-alpha01 or higher.
So you can write like this example.

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        setSupportActionBar(toolbar)

        lifecycleScope.launch { 
            val data = withContext(Dispatchers.IO) {
                loadData()
            }
            initUi(data)
        }
    }
    ...
}

In Fragment, use viewLifecycleOwner.

class MyFragment: Fragment() {
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        viewLifecycleOwner.lifecycleScope.launch { 
            val data = withContext(Dispatchers.IO) {
                loadData()
            }
            initUi(data)
        }
    }
    ...
}

Because LifecycleScope is lifecycle-aware, so if you want to use asynchronous tasks with only Activity and Fragment lifecycle scopes, it makes more sense to use LifecycleScope than GlobalScope.

See more: https://developer.android.com/topic/libraries/architecture/coroutines