Write/erase a text one caracter after another.

Typewriter.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Events;

using TMPro;

public class Typewriter : MonoBehaviour {
	static readonly string format = @"{0}<alpha=#00>{1}</color>{2}";

	public bool playOnAwake = false;
	public bool clearOnAwake = false;
	[Space]
	public float frequency = 10;
	public float delay = 0.25f;
	public TextMeshProUGUI textIn;
	public TextMeshProUGUI textOut;

	public UnityEvent onTypingFinished;

	void Start(){
		if (playOnAwake)
			this.SetText(textIn.text);
		else if (clearOnAwake)
			textIn.text = string.Empty;
		
		if (textOut && clearOnAwake)
			textOut.text = string.Empty;
	}

	public void SetText(string newText){
		this.StartCoroutine(Erase(textIn.text));
		textIn.text = string.Empty;
		this.StartCoroutine(Write(newText, delay));
	}

	IEnumerator Write(string message, float delay){
		yield return new WaitForSeconds(delay);

		for (int i=1; i<=message.Length; i++){
			int invisibleLength = message.Length - i;

			string visible = message.Substring(0, i);
			string invisible = message.Substring(i, invisibleLength);

			textIn.text = string.Format(format, visible, invisible, null);
			yield return new WaitForSeconds(1/frequency);
		}
		textIn.text = message;
		onTypingFinished.Invoke();
	}

	IEnumerator Erase(string message){
		if (!textOut)
			yield break;

		for (int i=1; i<=message.Length; i++){
			int visibleLength = message.Length - i;

			string invisible = message.Substring(0, i);
			string visible = message.Substring(i, visibleLength);

			textOut.text = string.Format(format, null, invisible, visible);
			yield return new WaitForSeconds(1/frequency);
		}
		textOut.text = string.Empty;
	}

}

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