**Function: Print some text to screen when run game on real devices. Must be built in Development build to take effect (that's good because you don't have to care about removing it in final build)

Debugf.cs

using UnityEngine;
using System.Collections;

/* by FVS - Ha Luan */

public class Debugf : MonoBehaviour
{
    #region Instance
    static Debugf instance = null;
    static Debugf Instance
    {
        get
        {
            if (instance == null)
            {
                Debugf debugf = new GameObject() { name = "Device logger" }.AddComponent<Debugf>();
                debugf.Init();
                DontDestroyOnLoad(debugf);
                instance = debugf;
                return instance;
            }
            else
            {
                return instance;
            }
        }
    }

    void Awake()
    {
        if (instance == null)
        {
            instance = this;
            Init();
            DontDestroyOnLoad(instance);
        }
        else
        {
            if (instance == this)
            {
                return;
            }
            else
            {
                Destroy(this);
            }
        }
    }

    #endregion

    string logContent = "";
    bool isShown = true;
    GUIStyle guiStyle;

    bool inited = false;

    void Init()
    {
        if (!inited)
        {
            guiStyle = new GUIStyle()
            {
                fontSize = 20 * Mathf.Max(Screen.height, Screen.width) / 326
            };


        }

        ///
        inited = true;
    }

    public void OnGUI()
    {
        if (isShown)
        {
            DisplayLogContent();
        }
    }

    void DisplayLogContent()
    {
        GUI.Label(new Rect(0, 0, 1000, 1000), new GUIContent() { text = logContent }, guiStyle);
    }

    void Logf(string content)
    {
        logContent = "\n" + content + logContent;
    }

    void Clearf()
    {
        logContent = "";
    }
    #region Static public exposition
#if DEBUG
    public static void Log(string content)
    {
        Instance.Logf(content);
    }
    public static void Log(object content)
    {
        Instance.Logf(content.ToString());
    }
    public static void Clear()
    {
        Instance.Clearf();
    }
#else
     public static void Log(string content)
    {
        
    }
    public static void Log(object content)
    {
        
    }
    public static void Clear()
    {
        
    }
#endif
    #endregion


}