refactored place on plane

Assets/Scenes/SampleScene.unity

   m_Name: 
   m_EditorClassIdentifier: 
   m_LightEstimation: 0
-  m_TryToInstallUpdateIfNeeded: 1
+  m_AttemptUpdate: 1
 --- !u!4 &427002220
 Transform:
   m_ObjectHideFlags: 0
   m_Name: 
   m_EditorClassIdentifier: 
   m_Camera: {fileID: 282840813}
-  m_Scale: 1
 --- !u!4 &1335839535
 Transform:
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   m_Script: {fileID: 11500000, guid: 7d5359d5f13250e4485741ed685a32be, type: 3}
   m_Name: 
   m_EditorClassIdentifier: 
-  m_PlacedPrefab: {fileID: 1934569588295450, guid: b34b6c8f1206a6844b983e23b9da0441,
+  PlacedPrefab: {fileID: 1934569588295450, guid: b34b6c8f1206a6844b983e23b9da0441,
     type: 2}

Assets/Scripts/PlaceOnPlane.cs

 [RequireComponent(typeof(ARSessionOrigin))]
 public class PlaceOnPlane : MonoBehaviour
 {
-    [SerializeField]
-    [Tooltip("Instantiates this prefab on a plane at the touch location.")]
-    GameObject m_PlacedPrefab;
+    [SerializeField] [Tooltip("Instantiates this prefab on a plane at the touch location.")]
+    public GameObject PlacedPrefab;
-    /// <summary>
-    /// The prefab to instantiate on touch.
-    /// </summary>
-    public GameObject placedPrefab
-    {
-        get { return m_PlacedPrefab; }
-        set { m_PlacedPrefab = value; }
-    }
-
-    /// <summary>
-    /// The object instantiated as a result of a successful raycast intersection with a plane.
-    /// </summary>
-    public GameObject placedObject { get; private set; }
+    private List<ARRaycastHit> hits;
+    private bool spawnedPrefab = false;
+    private GameObject spawnedObject;
+    private ARSessionOrigin sessionOrigin;
-        m_SessionOrigin = GetComponent<ARSessionOrigin>();
+        sessionOrigin = GetComponent<ARSessionOrigin>();
+        hits = new List<ARRaycastHit>();
-        if (Input.touchCount == 0)
-            return;
-
-        var touch = Input.GetTouch(0);
-
-        var hits = s_RaycastHits;
-        
-        if (!m_SessionOrigin.Raycast(touch.position, hits, TrackableType.PlaneWithinPolygon))
-            return;
-
-        placementHit = hits[0];
-    }
-
-    ARSessionOrigin m_SessionOrigin;
-
-    ARRaycastHit m_PlacementHit;
-
-    ARRaycastHit placementHit
-    {
-        get { return m_PlacementHit; }
-        set
+        if (Input.touchCount > 0)
-            m_PlacementHit = value;
+            Touch touch = Input.GetTouch(0);
-            if (placedObject == null && m_PlacedPrefab != null)
+            if (!spawnedPrefab)
-                placedObject = Instantiate(m_PlacedPrefab);
+                if (touch.phase == TouchPhase.Began)
+                {
+                    if (sessionOrigin.Raycast(touch.position, hits, TrackableType.PlaneWithinPolygon))
+                    {
+                        Pose hitPose = hits[0].pose;
+                       
+                        spawnedObject = Instantiate(PlacedPrefab, hitPose.position, hitPose.rotation);
+                        spawnedPrefab = true;                    
+                    }
+                }
-
-            if (placedObject != null)
+            else
-                var pose = m_PlacementHit.pose;
-                placedObject.transform.position = pose.position;
-                placedObject.transform.rotation = pose.rotation;
+                if (sessionOrigin.Raycast(touch.position, hits, TrackableType.PlaneWithinPolygon))
+                {
+                    Pose hitPose = hits[0].pose;
+                    spawnedObject.transform.position = hitPose.position;                 
+                }
-
-    List<ARRaycastHit> s_RaycastHits = new List<ARRaycastHit>();
 }