Your Second Kotlin Android App - Part 23: Returning | Ray Wenderlich

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1

Activities not only present layouts to the user, but they can also provide data to other activities.

This is a companion discussion topic for the original entry at https://www.raywenderlich.com/4534-your-second-kotlin-android-app/lessons/23
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Hey man, quick question. if the user switches between apps or even closes the app in Detail view how can we save the data? is there a preferred way of doing it like override fun onBackPressed() { in Android, is it won’t be called. thank you!

3

Hi cem. Normally you would do this in the Activity lifecycle onPause() method, and retrieve it in onResume().

4

hey shouldn’t it be data?.let {
listDataManager.saveList(it.getParcelableExtra(INTENT_LIST_KEY))
}
lines 98 and 99
thanks!

5

@bdmoakley Can you please help with this when you get a chance? Thank you - much appreciated! :]

6

How’s so? Would you mind clarifying your question?

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Hey, I was wondering about smart casting because sometimes it doesn’t work (not in that case). This is why I thought it would require ‘it’ or for example {data →
I sometimes get Smart cast to xxx is impossible because ‘x’ is mutable property…

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Hi standinga, thanks for the clarification! Not sure if I have the entire context of the question, but yes, using let when the nullable is mutable is the way to go.

data?.let {
  listDataManager.saveList(it.getParcelableExtra(INTENT_LIST_KEY))
}

This is equivalent to putting the nullable into a val and then doing a null check that does a smart cast:

val dataValue = data
if (dataValue != null) {
  listDataManager.saveList(dataValue.getParcelableExtra(INTENT_LIST_KEY))
}

I hope that answers your question. Let us know if not. Thanks!

9

Yes my confusion when asking question was about mutable nullable vs non-mutable (where smart cast is possible). It’s all clear now. BTW. Awesome course!!!

10

Thanks Joe! I appreciate the response. Cheers!

11

Hi, this was a great tutorial!
In the onActivityResult function in the main activity, you update the recycler view by creating a new recycler view adapter and passing to it the list read from the data manager. Isn’t this a very time consuming task? Because in the the first recycler view might have a long list of items and when we update one of the items, we re-read the whole list from the systems preferences. Wouldn’t it be better to just update the specific item in the list contained in the recycler view adapter? I hope I was clear with my question. Thank you!

12

@bdmoakley Can you please help with this when you get a chance? Thank you - much appreciated! :]