Touch Input & Mobile Swipe Detection

Question

I have written the following program to detect touch input with mouse as well as swipe input on a mobile device.

The mobile part works great with the Unity's Device Simulator. However, the mouse part throws the following error:

IndexOutOfRangeException: Index was outside the bounds of the array.

What am I missing here?

using UnityEngine;

public class SwipeDetection : MonoBehaviour
{
    public Player _Player;

    private Vector2 _startPos;

    private bool _fingerDown;

    public int _PixelDistToDetect = 50;


    private void Start()
    {
        _startPos = transform.position;
    }


    private void Update()
    {
        #region MOBILE TOUCH

        if (!_fingerDown && Input.touchCount > 0 && Input.touches[0].phase == TouchPhase.Began)
        {
            _fingerDown = true;
            _startPos = Input.touches[0].position;
        }

        if (_fingerDown)
        {
            if (Input.touches[0].position.y >= _startPos.y + _PixelDistToDetect)                // up
            {
                _fingerDown = false;                                                            Debug.Log( string.Format("<color=red><b><size=15> UP </size></b></color>") );
            }
            else if (Input.touches[0].position.x <= _startPos.x - _PixelDistToDetect)           // left
            {
                _fingerDown = false;                                                            Debug.Log( string.Format("<color=red><b><size=15> LEFT </size></b></color>") );
            }
            else if (Input.touches[0].position.x >= _startPos.x + _PixelDistToDetect)           // right
            {
                _fingerDown = false;                                                            Debug.Log( string.Format("<color=red><b><size=15> RIGHT </size></b></color>") );
            }
            else if (Input.touches[0].position.y <= _startPos.y - _PixelDistToDetect)           // down
            {
                _fingerDown = false;                                                            Debug.Log( string.Format("<color=red><b><size=15> DOWN </size></b></color>") );
            }
        }

        if (_fingerDown && Input.touchCount > 0 && Input.touches[0].phase == TouchPhase.Ended)
        {
            _fingerDown = false;
        }

        #endregion MOBILE TOUCH
        
        #region MOUSE DRAG

        if (!_fingerDown && Input.GetMouseButtonDown(0))
        {
            _fingerDown = true;
            _startPos = Input.mousePosition;
        }

        if (_fingerDown)
        {
            if (Input.mousePosition.y >= _startPos.y + _PixelDistToDetect)                      // up
            {
                _fingerDown = false;                                                            Debug.Log( string.Format("<color=red><b><size=15> UP </size></b></color>") );
            }
            else if (Input.mousePosition.x <= _startPos.x - _PixelDistToDetect)                 // left
            {
                _fingerDown = false;                                                            Debug.Log( string.Format("<color=red><b><size=15> LEFT </size></b></color>") );
            }
            else if (Input.mousePosition.x >= _startPos.x + _PixelDistToDetect)                 // right
            {
                _fingerDown = false;                                                            Debug.Log( string.Format("<color=red><b><size=15> RIGHT </size></b></color>") );
            }
            else if (Input.mousePosition.y <= _startPos.y - _PixelDistToDetect)                 // down
            {
                _fingerDown = false;                                                            Debug.Log( string.Format("<color=red><b><size=15> DOWN </size></b></color>") );
            }
        }

        if (_fingerDown && Input.GetMouseButtonUp(0))
        {
            _fingerDown = false;
        }

        #endregion MOUSE DRAG
    }
}

Answer 1

because you code (in Mobile Drag section) set _fingerDown to true So, next frame update call

 if (_fingerDown) ...

on Mobile touch section and Input.touch always null (while on pc) and you invoke Input.touches[0] that way IndexOutOfBound are thrown