TextViewWriter

attrs.xml

<resources>
  <declare-styleable name="TextViewWriter">
    <attr name="delay" format="integer"/>
    <attr name="autoStart" format="boolean"/>
    <attr name="mode" format="enum">
      <enum name="character" value="0"/>
      <enum name="word" value="1"/>
    </attr>
  </declare-styleable>
</resources>

TextViewWriter.java

public class TextViewWriter extends TextView {
  private static final int DEFAULT_DELAY_MS = 150;
  private static final boolean DEFAULT_AUTOSTART = false;

  public static final int MODE_CHARACTER = 0;
  public static final int MODE_WORD = 1;
  private static final int DEFAULT_MODE = MODE_CHARACTER;

  @Retention(RetentionPolicy.SOURCE) @IntDef({ MODE_CHARACTER, MODE_WORD }) public @interface Mode {
  }

  private CharSequence text;
  private int index;
  private long delay;
  private int mode;

  private boolean paused;
  private boolean running;

  private ArrayList<TextViewWriterListener> listeners;

  private final Handler handler = new Handler();

  public TextViewWriter(Context context) {
    this(context, null);
  }

  public TextViewWriter(Context context, AttributeSet attrs) {
    this(context, attrs, 0);
  }

  public TextViewWriter(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    init(context, attrs);
  }

  @TargetApi(Build.VERSION_CODES.LOLLIPOP)
  public TextViewWriter(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
    super(context, attrs, defStyleAttr, defStyleRes);
    init(context, attrs);
  }

  private void init(Context context, AttributeSet attrs) {
    TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.TextViewWriter);
    delay = typedArray.getInt(R.styleable.TextViewWriter_delay, DEFAULT_DELAY_MS);
    mode = typedArray.getInt(R.styleable.TextViewWriter_mode, DEFAULT_MODE);
    boolean autoStart =
        typedArray.getBoolean(R.styleable.TextViewWriter_autoStart, DEFAULT_AUTOSTART);
    typedArray.recycle();

    if (autoStart) {
      playOrResume();
    }
  }

  public void addTextViewWriterListener(TextViewWriterListener listener) {
    if (listeners == null) {
      listeners = new ArrayList<>();
    }
    listeners.add(listener);
  }

  public void removeTextViewWriterListener(TextViewWriterListener listener) {
    if (listeners != null) {
      int position = listeners.indexOf(listener);
      if (position >= 0) {
        listeners.remove(position);
      }
    }
  }

  public void clearTextViewWriterListener() {
    if (listeners != null) {
      for (TextViewWriterListener listener : listeners) {
        removeTextViewWriterListener(listener);
      }
      listeners.clear();
      listeners = null;
    }
  }

  private final Runnable runnable = new Runnable() {
    @Override public void run() {
      if (text == null) {
        text = "";
      }

      running = true;
      if (mode == MODE_CHARACTER) {
        index++;
      } else {
        int spaceIndex = text.toString().indexOf(" ", index);
        if (spaceIndex != -1) {
          index = spaceIndex + 1;
        } else {
          index = text.length();
        }
      }

      setText(text.subSequence(0, index));

      if (index < text.length() && !paused) {
        handler.postDelayed(runnable, delay);
      } else {
        running = false;
        notifyFinish();
      }
    }
  };

  public void play(CharSequence text) {
    super.setText(text);
    this.text = text;
    index = 0;
    run();
  }

  public void play(CharSequence text, int from) {
    super.setText(text);
    index = from;
    run();
  }

  public void play(int from) {
    text = getText();
    index = from;
    run();
  }

  public void playOrResume() {
    if (getText().equals(text)) {
      if (!paused) {
        index = 0;
      }
    } else {
      text = getText();
      index = 0;
    }
    run();
  }

  public void pause() {
    paused = true;
    notifyPause();
  }

  public void stop() {
    paused = true;
    index = 0;
    notifyStop();
  }

  public void end() {
    paused = true;
    setText(text);
  }

  private void run() {
    paused = false;
    if (text != null && text.length() > 0) {
      if (index > text.length()) {
        index = text.length();
      }
      setText("");
      if (!running) {
        handler.removeCallbacks(runnable);
        handler.postDelayed(runnable, delay);
      }
      notifyStart();
    }
  }

  public int getIndex() {
    return index;
  }

  public void setIndex(int index) {
    this.index = index;
    playOrResume();
  }

  public long getDelay() {
    return delay;
  }

  public void setDelay(long delay) {
    this.delay = delay;
    playOrResume();
  }

  public @Mode int getMode() {
    return mode;
  }

  public void setMode(@Mode int mode) {
    this.mode = mode;
    playOrResume();
  }

  private void notifyStop() {
    if (listeners != null) {
      for (TextViewWriterListener listener : listeners) {
        listener.onStop();
      }
    }
  }

  private void notifyPause() {
    if (listeners != null) {
      for (TextViewWriterListener listener : listeners) {
        listener.onPause(index);
      }
    }
  }

  private void notifyStart() {
    if (listeners != null) {
      for (TextViewWriterListener listener : listeners) {
        listener.onStart();
      }
    }
  }

  private void notifyFinish() {
    if (listeners != null) {
      for (TextViewWriterListener listener : listeners) {
        listener.onFinish();
      }
    }
  }
}

TextViewWriterListener.java

public interface TextViewWriterListener {
  void onStart();

  void onPause(int index);

  void onStop();

  void onFinish();
}