producing a typewriter-like effect

Question

Android newb here. Please use small words :-)

I'd like to simulate typewriter output on my Android. The output being displayed is generated by a game and is somewhat freeform. The effect I want to see individual characters appear at a rate of about 6 characters a second. When a 'carriage return' is seen, I'd like to insert a delay then resume typing on the left.

What are some suggestions on views? Would the view of choice for this be a TextView? Even that seems like overkill for this read-only coarsely scrolling output.

I saw something on this thread about an AsyncTask. That looks useful. Perhaps my game will write to some manner of buffer, and a subclass of AsyncTask will pull a character out every .15 seconds or so, add it to the TextView, then invalidate() the TextView? Sound like a plan?

Resolution:

I wrapped the TextView in the ScrollView and it worked fine. The suggested 'TextView.append()' also did the job, as expected. I had trouble with the scroll.FullScroll(), however. Apparently this has to be executed using a Runnable from the scroll.post() method. I don't know why, exactly, but I'll dig into that later. There are a number of SO threads about it.

score 2 · Accepted Answer · answered Apr 01 '12 at 23:40

2

Would the view of choice for this be a TextView?

A TextView wrapped in a ScrollView seems likely:

  <ScrollView android:id="@+id/scroll"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
  >
    <TextView android:id="@+id/transcript"
      android:layout_width="match_parent" 
      android:layout_height="wrap_content" 
    />
  </ScrollView>

Sound like a plan?

You do not need an AsyncTask for this. Use postDelayed() on your TextView or something to schedule a Runnable to run in 166 milliseconds. That Runnable will:

Append your character to your TextView
Scroll the ScrollView to the bottom (in case you have exceeded what fits on the screen)
Schedules itself via postDelayed() to run in another 166 milliseconds

The first two bullets would look like:

transcript.append(yourCharacter);
scroll.fullScroll(View.FOCUS_DOWN);

Things will not be completely even, as that 166ms is a minimum time before the Runnable runs. OTOH, slightly irregular delivery of keys would accentuate the typewriter effect.

answered Apr 01 '12 at 23:40

CommonsWare

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I see that TextView has a scrolling facility. What's the value in wrapping it in ScrollView? – Tony Ennis Apr 02 '12 at 00:02
@TonyEnnis: I am not sure what "scrolling facility" you are referring to. All widgets have properties and methods related to scrolling, but they do not scroll themselves -- they need to be in a scrollable container. You *might* be able to avoid the `ScrollView` with appropriate settings for the `TextView's` gravity, but then the user would not be able to scroll up to read the rest. – CommonsWare Apr 02 '12 at 11:15
According to the ScrollView doc at http://developer.android.com/reference/android/widget/ScrollView.html, "The TextView class also takes care of its own scrolling, so does not require a ScrollView, but using the two together is possible to achieve the effect of a text view within a larger container." I'll reread it this evening. – Tony Ennis Apr 02 '12 at 11:19
@TonyEnnis: They must have added that sentence within the past couple of years... :-) Feel free to give it a shot. – CommonsWare Apr 02 '12 at 11:26
It didn't work because to make a TextView scroll one needs to define a scrolling method: _TexView.setMovementMethod(new ScrollingMovementMethod())_ If instead one wraps it in a ScrollView then the definition isn't needed. I did it the way you suggested and it worked fine. – Tony Ennis Apr 03 '12 at 11:14
Inspired by the discussion over at http://stackoverflow.com/questions/6700374/android-character-by-character-display-text-animation/6700718#6700718 I created a gist of a TypewriterView that can animate typing and deleting, pause and run arbitrary Runnables. Glad to share if it can help anyone https://gist.github.com/claudijo/0cf9f43705efadfeb852 – Claudijo Nov 19 '15 at 09:46

producing a typewriter-like effect

1 Answers1