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.

Answer 1

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.