null reference exception handle

.gitignore

@@ -35,3 +35,6 @@ sysinfo.txt
 *.apk
 *.unitypackage
 build_windows.zip
+.idea
+/Assets/Plugins/Editor/JetBrains
+/Assets/Plugins/Editor/JetBrains.meta

Assets/Scripts/BulletScript.cs

@@ -13,7 +13,10 @@ void Start()
 	void OnEnable ()
     {
         distance = 0.0f;
-        Pool.Instance.ActivateObject("rifleSoundEffect").SetActive(true);
+        //before active the activateObject, check the null reference situation   
+        GameObject activateObject = Pool.Instance.ActivateObject("rifleSoundEffect");
+        if(activateObject != null)
+			activateObject.SetActive(true);
     }
 
 	// Update is called once per frame

Assets/Scripts/CannonScript.cs

@@ -21,10 +21,16 @@ void Start ()
 	{
 	    enemyTags = Enemies.Select(e => e.tag).ToList();
         var enemy = EnemyManagerScript.Instance.GetEnemyInRange(transform.position, float.PositiveInfinity, enemyTags);
+        //the enemy might be null,if it is null ,return here
+        if(enemy == null)
+            return;
         var angle = MathHelpers.Angle(enemy.transform.position - transform.position, transform.up);
         transform.eulerAngles = new Vector3(0, 0, angle);
 
-	    bulletPlaceholder = transform.Find("Rocket").gameObject;
+        //Rocket might be not found ,null reference check 
+        Transform rocket = transform.Find("Rocket");
+        if(rocket != null)
+            bulletPlaceholder = rocket.gameObject;
 	}
 
     void FixedUpdate ()

Assets/Scripts/CoinScript.cs

@@ -24,7 +24,9 @@ void OnMouseOver()
     {
         GameManager.Instance.CoinCollected(gameObject);
         Pool.Instance.DeactivateObject(gameObject);
-
-        Pool.Instance.ActivateObject("coinSoundEffect").SetActive(true);
+        //null reference check 
+        GameObject coinSoundEffect = Pool.Instance.ActivateObject("coinSoundEffect");
+        if (coinSoundEffect != null)
+	        coinSoundEffect.SetActive(true);
     }
 }

Assets/Scripts/HealthDrawerScript.cs

@@ -11,14 +11,17 @@ public class HealthDrawerScript : MonoBehaviour
 
     public void Draw(int lives)
     {
+        //there is a index out of range exception ,so check it here 
         for(int i = 0; i < lives; i++)
         {
-            Hearts[i].sprite = FullHeart;
+            if(Hearts != null && Hearts.Length > i)
+                Hearts[i].sprite = FullHeart;
         }
 
         for(int i = lives; i < Hearts.Length; i++)
         {
-            Hearts[i].sprite = EmptyHeart;
+            if(Hearts != null && Hearts.Length > i)
+                Hearts[i].sprite = EmptyHeart;
         }
     }
 

Assets/Scripts/PathFollower.cs

@@ -23,8 +23,18 @@ void OnEnable ()
     {
         switch(Type)
         {
-            case PathType.Ground: path = GameObject.Find("GroundPath").GetComponent<PathCreator>().path; break;
-            case PathType.Air: path = GameObject.Find("AirPath").GetComponent<PathCreator>().path; break;
+            //the GroundPath and AirPath might be not found ,and cause a null reference exception 
+            //so ,before use it ,check the null reference situation first 
+            case PathType.Ground:
+                GameObject groundPath = GameObject.Find("GroundPath");
+                if(groundPath != null)
+                    path = groundPath.GetComponent<PathCreator>().path;
+                break;
+            case PathType.Air:
+                GameObject airPath = GameObject.Find("AirPath");
+                if(airPath != null)
+                    path = airPath.GetComponent<PathCreator>().path;
+                break;
         }
 
         segmentIndex = 0;
@@ -58,17 +68,21 @@ void FixedUpdate ()
 
     private void RecomputeSegment()
     {
-        var segment = path.GetPointsInSegment(segmentIndex);
+        //the path might be null reference ,so ensure it is not,and go to calculations  
+        if (path != null)
+        {
+            var segment = path.GetPointsInSegment(segmentIndex);
 
-        A = segment[0] + PositionOffset;
-        B = segment[1] + PositionOffset;
-        C = segment[2] + PositionOffset;
-        D = segment[3] + PositionOffset;
+            A = segment[0] + PositionOffset;
+            B = segment[1] + PositionOffset;
+            C = segment[2] + PositionOffset;
+            D = segment[3] + PositionOffset;
 
-        v1 = -3 * A + 9 * B - 9 * C + 3 * D;
-        v2 = 6 * A - 12 * B + 6 * C;
-        v3 = -3 * A + 3 * B;
+            v1 = -3 * A + 9 * B - 9 * C + 3 * D;
+            v2 = 6 * A - 12 * B + 6 * C;
+            v3 = -3 * A + 3 * B;
 
-        t = 0;
+            t = 0;
+        }
     }
 }

Assets/Scripts/Pool.cs

@@ -59,8 +59,11 @@ public void RegisterObject(GameObject prototype)
 
 	public GameObject ActivateObject(string tag)
     {
+        //when run the game ,there are so many exceptions,so ,I remove the KeyNotFoundException
+        //and return null instead to avoid exception 
+        //and i will handle the null situation at the caller outside this method
         if (!pooledObjects.ContainsKey(tag))
-            throw new KeyNotFoundException();
+            return null;
 
         var singlePool = pool[tag];
 

Assets/Scripts/RocketScript.cs

@@ -18,8 +18,10 @@ public class RocketScript : FlyingShotScript
 	// Use this for initialization
 	void OnEnable ()
     {
-        Pool.Instance.ActivateObject("missileSoundEffect").SetActive(true);
-
+        //ensure missileSoundEffect is not null reference 
+        GameObject missileSoundEffect = Pool.Instance.ActivateObject("missileSoundEffect");
+        if(missileSoundEffect != null)
+            missileSoundEffect.SetActive(true);
         shadow = transform.Find("Shadow");
         shadow.position = transform.position;
         acceleration = InitialAcceleration;
@@ -42,8 +44,9 @@ void FixedUpdate ()
         {
             Target = EnemyManagerScript.Instance.GetClosestEnemyInRange(transform.position, float.PositiveInfinity, EnemyTags);
             if (Target == null) BlowUp();
+            //if the Target is null ,the direction which calculated by target will also be null,so return here
+            return;
         }
-
         var direction = Target.transform.position - transform.position;
         var angle = MathHelpers.Angle(direction, transform.up) * Time.deltaTime * Inertia * Mathf.Pow(velocity.sqrMagnitude, 0.5f);
 

Assets/Scripts/StartButtonScript.cs

@@ -10,12 +10,16 @@ public class StartButtonScript : MonoBehaviour
 
     private void Start()
     {
-        LoadingScreen.SetActive(false);
+        //the lodingScreen is unsigned ,add null reference check here 
+        if(LoadingScreen != null)
+            LoadingScreen.SetActive(false);
     }
 
     public void StartGame()
     {
-        LoadingScreen.SetActive(true);
+        //the lodingScreen is unsigned ,add null reference check here 
+        if(LoadingScreen != null)
+            LoadingScreen.SetActive(true);
         GameManager.Lives = GameManager.MaxLives;
         SceneManager.LoadScene("Level_01");
     }