Cornell lec01

Activity and intent

intents

Explict intents calls antther oncreate() method of anther activity

To transition to a new activity, we first create an intent with the following code

var intent = Intent(this, TargetActivity::class.java)

The .java is some sort of convention, though it might seem wierd. To launch an activity with the given intent, we write
 startActivity(intent)

To close

finish()

send data

include info within intent. we write

putExtra(key, value)

This stores everythings in a bundle

receive data

// eateryName = "Okenshields"
var eateryName = getIntent().extras?.getString("EATERY_NAME")

send back info

In the above content, we have implemented function like launching a new activity, sending info from current acti to target acti. And now, we wonder how to send data back to a launched acti Introduction a new method

// In MainActivity.kt
registerForActivityResult(ActivityResultContract, ActivityResultCallback)

private lateinit var intentLauncher: ActivityResultLauncher<Intent>
// ...
intentLauncher = registerForActivityResult(
   ActivityResultContracts.StartActivityForResult()
) {
   result ->
   if (result.resultCode == SOME_UNIQUE_INTEGER) {
       val hi = result.data?.extras?.get("hi")
       println("MainMain")
       binding.textviewId.text = hi as String
    }
   }
  // ...
   intentLauncher.launch(intent) // use intentLauncher
   // ...

 companion object {
        // Can be referenced both within the MainActivity and other
        // Activities (e.g. your TargetActivity)
        const val SOME_UNIQUE_INTEGER = 1

we mark the return value of above code as intentLauncher and use intentLauncher.launch() to load intent, instead of startActivity.

In targetActivity

we create a new intent, load info, and setResult

override fun onBackPressed() {
     val intent = Intent()
     println("asasasa")
     intent.putExtra("hi", "hi")
     setResult(SOME_UNIQUE_INTEGER, intent)
     super.onBackPressed()
}
// Interger 作为resultCode, 可以利用它来标记多种功能

implicit intent

implicit means we do not call onCreate method. It is a feature that allows us to communicate among other apps