android Activity static starter method in Kotlin

Question

In java, one can define a starter static method for an Activity. In Android Studio, there is even a "starter" template for it: it would look something like this:

public class MyActivity extends AppCompatActivity {

    private static final String EXTRA_FOO = "foo";

    public static void start(Context caller, String bar){
        Intent intent = new Intent(caller, MyActivity.class);
        intent.putExtra(EXTRA_FOO, bar);
        caller.startActivity(intent);
    }
}

I'm wrapping my head around this same concept in Kotlin and the closest thing I came up with looks like this:

class MyActivity : AppCompatActivity() {

    companion object {
        private val EXTRA_FOO = "foo"

        fun start(caller: Context, bar: String){
            val intent = Intent(caller, MyActivity::class.java)
            intent.putExtra(EXTRA_FOO, bar)
            caller.startActivity(intent)
        }
    }
}

Is there a more concise and elegant way to do this? I can't believe this is the way to go, it looks uglier than in Java. Also, there is no "starter" template for Kotlin.

Answer 1

There are a few approaches you could take. I'm a fan of extension functions:

class MyActivity : AppCompatActivity()

private fun Intent.extraFoo(bar : String) = putExtra("foo", bar)

fun Context.startMyActivity(bar : String) =
    Intent(this, MyActivity::class.java).apply { extraFoo(bar) }.let(this::startActivity)

This creates an extension to Context so that you can call startMyActivity on any Context object.

---

Here's that same extension function in a more Java-like style, so you can compare it more easily to what you already have:

private val EXTRA_FOO = "foo"

fun Context.startMyActivity(bar : String) {
    val intent = Intent(this, MyActivity::class.java)
    intent.putExtra(EXTRA_FOO, bar)
    startActivity(intent)
}