Kotlin - idiomatic way to create a Fragment newInstance pattern

Question

The best practice on Android for creating a Fragment is to use a static factory method and pass arguments in a Bundle via setArguments().

In Java, this is done something like:

public class MyFragment extends Fragment {     static MyFragment newInstance(int foo) {         Bundle args = new Bundle();         args.putInt("foo", foo);         MyFragment fragment = new MyFragment();         fragment.setArguments(args);         return fragment;     } } 

In Kotlin this converts to:

class MyFragment : Fragment() {     companion object {        fun newInstance(foo: Int): MyFragment {             val args = Bundle()             args.putInt("foo", foo)             val fragment = MyFragment()             fragment.arguments = args             return fragment         }     } } 

This makes sense to support interop with Java so it can still be called via MyFragment.newInstance(...), but is there a more idiomatic way to do this in Kotlin if we don't need to worry about Java interop?

Answer 1

I like to do it this way:

companion object {     private const val MY_BOOLEAN = "my_boolean"     private const val MY_INT = "my_int"      fun newInstance(aBoolean: Boolean, anInt: Int) = MyFragment().apply {         arguments = Bundle(2).apply {             putBoolean(MY_BOOLEAN, aBoolean)             putInt(MY_INT, anInt)         }     } } 

Edit: with KotlinX extensions, you can also do this

companion object {     private const val MY_BOOLEAN = "my_boolean"     private const val MY_INT = "my_int"      fun newInstance(aBoolean: Boolean, anInt: Int) = MyFragment().apply {         arguments = bundleOf(             MY_BOOLEAN to aBoolean,             MY_INT to anInt)     } } 

Answer 2

inline fun <reified T : Fragment>     newFragmentInstance(vararg params: Pair<String, Any>) =     T::class.java.newInstance().apply {         arguments = bundleOf(*params)     }` 

So it is used like that:

val fragment = newFragmentInstance<YourFragment>("key" to value) 

Credit

bundleOf() can be taken from Anko