How to detect touch on any gameObject in Unity

Background

You can have multiple GameObjects on your scene in Unity. How can we determine if user has touched a particular element. We will see how in this post. We will use Physics2D.Raycast() for this.

Code 

You can do something like following -

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

public class GameInputs : MonoBehaviour {

    // Use this for initialization
    void Start () {
        
    }
    
    // Update is called once per frame
    void Update () {

        //We check if we have one or more touch happening.
        //We also check if the first touches phase is Ended (that the finger was lifted)
        if (Input.touchCount > 0 && Input.GetTouch (0).phase == TouchPhase.Ended) {
            //We transform the touch position into word space from screen space and store it.
            Vector3 touchPosWorld = Camera.main.ScreenToWorldPoint(Input.GetTouch(0).position);
            Vector2 touchPosWorld2D = new Vector2(touchPosWorld.x, touchPosWorld.y);
            //Debug.Log("Touched " + touchPosWorld.x + "" +  touchPosWorld.y);
            //We now raycast with this information. If we have hit something we can process it.
            RaycastHit2D hitInformation = Physics2D.Raycast (touchPosWorld2D, Camera.main.transform.forward);
            if (hitInformation.collider != null) {
                //We should have hit something with a 2D Physics collider!
                GameObject touchedObject = hitInformation.transform.gameObject;
                //touchedObject should be the object someone touched.
                Debug.Log("Touched " + touchedObject.transform.name);
                switch (touchedObject.tag) {
                case "StartGameButton":
                    Debug.Log("Touched StartGameButton " + touchedObject.transform.name);
                    break;
                case "LikeButton":
                    Debug.Log("Touched LikeButton " + touchedObject.transform.name);
                    Application.OpenURL("https://play.google.com/store/apps/details?id=com.osfg.ringtonesetter.main");
                    Application.OpenURL("market://details?id=com.osfg.ringtonesetter.main"); 
                    break;
                case "SettingsButton":
                    Debug.Log ("Touched SettingsButton " + touchedObject.transform.name);
                    Application.LoadLevel ("Settings");
                    break;
                }
            }

        }
    }
}

Explanation and setup

As you can see we are using Physics2D.Raycast() to case a ray from camera to point of touch and then detecting a collision. Finally if we have collision information we check the tag associated with it to check out element of interest.

1. Make sure for each such elements you add a collider component like 2D Box collider. Only then collision will work.
2. Make sure you tag each elements correctly and use it to get your object when touched.

Other Notes :

1. You can create a prefab of background and use it in all your app screens to be consistent. That way changes made in prefab will be applicable to all instances of it.
2. If your scene is not getting correctly displayed you can correct it by clicking on "Main Camera" and then Game Object -> Align view to selected