Android retrieving a result from an Activity #Android

declare a callback for receiving the result from the Activity - MainActivity.kt

    
	/*    This exercise introduced you to another way of creating user flows using registerFor
    ActivityResult. This can be very useful for carrying out a dedicated Task where you need a
    result before proceeding with the user’s flow through the app.
    */
	private val startForResult = registerForActivityResult(
        ActivityResultContracts.StartActivityForResult()
    ) { activityResult ->
        val data = activityResult.data
        val backgroundColor = data?.getIntExtra(RAINBOW_COLOR, Color.parseColor(DEFAULT_COLOR)) ?: Color.parseColor(DEFAULT_COLOR)
        val colorName = data?.getStringExtra(RAINBOW_COLOR_NAME) ?: ""
        val colorMessage = getString(R.string.color_chosen_message, colorName)
        val rainbowColor = findViewById<TextView>(R.id.rainbow_color)
        rainbowColor.setBackgroundColor(ContextCompat.getColor(this, backgroundColor))
        rainbowColor.text = colorMessage
        rainbowColor.isVisible = true
    }

fire a Indent with extra Data (putExtra) - ResultActivity.kt

    private fun setRainbowColor(colorName: String, color: Int) {
        Intent().let { pickedColorIntent ->
            pickedColorIntent.putExtra(RAINBOW_COLOR_NAME, colorName)
            pickedColorIntent.putExtra(RAINBOW_COLOR, color)
            setResult(
                Activity.RESULT_OK,
                pickedColorIntent
            )
            finish()
        }
    }
    
    
   // The `setRainbowColor` function creates an intent
   // The result is then returned to the calling Activity, 
   // you call `finish()` so that the calling Activity is displayed.
   // The way that you retrieve the rainbow color that the user has chosen is by adding a listener for all the buttons in the layout.

note.md

Retrieving a result from an Activity

For some user flows, you will only launch an Activity for the sole purpose of retrieving a result back from it.

This exercise introduced you to another way of creating user flows using registerFor ActivityResult. This can be very useful for carrying out a dedicated Task where you need a result before proceeding with the user’s flow through the app.

• You’ll be using the registerForActivityResult(ActivityResultContracts.StartActivityForResult()) function to get a result back from the Activity you launch.

Open Activity from where we need the result - MainActivity.kt

//  the logic to launch the Activity from the property defined previously	
findViewById<Button>(R.id.submit_button).setOnClickListener {
            startForResult.launch(
                Intent(this, RainbowColorPickerActivity::class.java) // Intent that is launched for its result!
            )
        }

// This creates an Intent that is launched for its result: `Intent(this, RainbowColor PickerActivity::class.java)`.

register onClickListener on the ResultActivity.kt

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_rainbow_color_picker)

        val colorPickerClickListener = View.OnClickListener { view ->
            when (view.id) {
                R.id.red_button -> setRainbowColor(getString(R.string.red), R.color.red)
                else -> {
                    Toast.makeText(this, getString(R.string.unexpected_color), Toast.LENGTH_LONG).show()
                }
            }
        }
        // The `colorPickerClickListener` added in the preceding code determines which colors to set for the `setRainbowColor(colorName: String, color: Int)` function by using a `when` statement.

        findViewById<View>(R.id.red_button).setOnClickListener(colorPickerClickListener)
   }