Fix cursor moving back and missing characters

[MJ1998]

IMPORTANT: All PRs must be linked to an issue (except for extremely trivial and straightforward changes).

Fixes #1914

Cause of the issue: The EditText temporarily contains an extra character. The TextWatcher gets removed (here) before it can process this extra character, leaving the saved text state (in QuestionnaireViewItem) inconsistent with the actual EditText content. This inconsistency triggers a UI update using EditText#setText (here), which unintentionally resets the cursor position to the beginning.

EditText#append moves the cursor to the last position.

Read comments in rest of the PR for more details.

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• I have read and acknowledged the Code of conduct.
• I have read the Contributing page.
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• I have discussed my proposed solution with code owners in the linked issue(s) and we have agreed upon the general approach.
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• I have built and run the demo app(s) to verify my change fixes the issue and/or does not break the demo app(s).

[MJ1998]

This, however, has a side effect (which existed earlier as well but was overlooked because of cursor resetting) of missing some characters when typing too fast.
Reason: EditText's extra character is skipped when using the above solution.

Solving this will require more effort. I can think of a solution which will involve detecting "user has stopped typing". Something like this - stackoverflow.

Let me know if you want to fix this as well. Will raise a separate issue for this.

Alternative: Use RxBindings or do some backpressure solutioning to handle all character inputs from user. But this will need a more complex handling - like "not updating the EditText until upstream processing (handleInput) is complete".

[pld]

@jingtang10 what are your thoughts on this?

[MJ1998]

I made an attempt at solving the "side effect" as well. Seems good to me but Idk if this behaviour - "detect user has stopped typing" can have any other side effects.

Only difficulty is to test this as racing conditions are always a pain to test.
How I tested it - Ran my finger over "QWERTY" tabs on keyboard back and forth really fast. Before the last commit I could see some missed characters. After the last commit, I didn't see any missed character in quite some attempts trying this test.

Can you try testing this PR ?
@pld

[AngelaKabari]

Thanks for all your work on this @MJ1998. @FikriMilano will test the PR tomorrow and we'll get back to you.

[FikriMilano]

Thanks @MJ1998, I like your first idea and it's working, in a nutshell -> only apply new answer to questionnaireViewItem after user stops typing for 0.5 second, if there are more inputs coming in, the answer won't be applied since the timer is canceled.

Not sure if it's worth it to introduce RxBinding right now.

override fun afterTextChanged(editable: Editable?) {
        timer?.cancel()
        // If editable has become empty or this is the first character then invoke afterTextChanged
        // instantly else start a timer for user to finish typing
        if (editable?.toString().isNullOrEmpty() || firstCharacter) {
          Log.d("FIKRI1", "$editable")
          afterTextChanged(editable?.toString())
        } else {
          // countDownInterval is simply kept greater than delay as we don't need onTick
          timer =
            object : CountDownTimer(delay, delay * 2) {
                override fun onTick(millisUntilFinished: Long) {}

                override fun onFinish() {
                  Log.d("FIKRI2", "$editable")
                  afterTextChanged(editable?.toString())
                }
              }
              .start()
        }
      }

2024-05-09 11:24:26.372  2316-2316  FIKRI1                  com.google.android.fhir.catalog      D  
2024-05-09 11:24:27.912  2316-2316  FIKRI1                  com.google.android.fhir.catalog      D  a
2024-05-09 11:24:30.037  2316-2316  FIKRI2                  com.google.android.fhir.catalog      D  aa
2024-05-09 11:24:35.997  2316-2316  FIKRI2                  com.google.android.fhir.catalog      D  aaqwertqwertqwertqwertqwert

qwerty.webm

[MJ1998]

Just FYI an elaboration on how I am testing this:-
I slide my finger and keep it pressed over "QWERTY" keys back and forth. So the input I generate is "qwertytrewqwertytrewq...".

You can observe some characters being missed before the last commit if you test like this. @FikriMilano

In actual case the upstream function can take more time to finish (for example, resolving fhir query) - which makes characters missing clearly visible.

[MJ1998]

Regarding your question on RxBinding, I think its a much bigger effort as we dont use simple TextView or EditText views, rather its a EditTextInputLayout which offers more features like validation, header views along with it.

So moving from EditTextInputLayout to RxBinding views will be difficult.
@FikriMilano

[FikriMilano]

@MJ1998 I agree, we can keep it this way for now

[AngelaKabari]

@MJ1998 this fix you shared is working great. Thank you for prioritising this and getting it resolved so quickly!

[AngelaKabari]

@MJ1998 upon further testing, the issue of the missing characters is significantly affecting the data entry.

Missing.letters.bug.webm

Can we please go back to the drawing board on this?

[MJ1998]

Is this issue happening on this PR?

[AngelaKabari]

@MJ1998 yes it is.

[MJ1998]

Gotcha. I had a feeling this will introduce more side effects.
Can you tell me if there is any expression in your questionnaire's items that are dependent (directly or indirectly) on this item being modified ?

[FikriMilano]

@MJ1998 there's none, it's just a normal text field