How do I call methods from other scripts using C#?

Question

I'm seriously stuck with this. I have 2 scripts; a Game Manager and a UI Manager. When you hit Esc the 'gamestate' in the Game manager is set to paused and from within it will call a method from the UI manager to display a 'paused' message on the screen.

I have 2 scenes. In the first scene which is the main menu, the Game manager is initialised and continue to exist throughout every scene. In the second scene, there is a empty game object with the UI Manager attached.

When I run the game, move to level 1, and the hit escape, I get the following errors:

 NullReferenceException: Object reference not set to an instance of an object
 Game_Manager.GamePause () (at Assets/Scripts/Game_/Game_Manager.cs:55)
 Game_Manager.Update () (at Assets/Scripts/Game_/Game_Manager.cs:46)

So it's claiming that the UI Manager does not exist and so it crashes. :(

Here are the scripts...

 /// Game Manager
 
 using System.Collections;
 using UnityEngine;
 
 enum GameState { mainmenu, playing, paused, gameover };
 
 public class Game_Manager : MonoBehaviour
 {
     private static Game_Manager thisInstance;
     private static GameState mGameState;
     private UI_Manager mUI;
     
 
     void Awake()
     {
         Screen.SetResolution(800, 600, false);
 
         /// Ensures that the GameManager is persistant through all scenes
         
         if (thisInstance != null && thisInstance != this) //IF we already has an instance of this class
             Destroy(gameObject);
         else
         {
             thisInstance = this;
             DontDestroyOnLoad(this);
         }
     }
 
     void Start()
     {
         Debug.Log("Game_Manager initialised");
         mGameState = GameState.mainmenu;
     }
 
     void Update()
     {
         if (mGameState == GameState.mainmenu)
         {
             GameMainMenu();
         }
 
         /// Pausing
         if (Input.GetKeyDown(KeyCode.Escape))
         {
             GamePause();
         }
     }
 
     public void GamePause()
     {
         if (mGameState == GameState.playing)
         {
             mUI.GamePauseGUI();
             Time.timeScale = 0.0f;
             mGameState = GameState.paused;
             Debug.Log("Game Paused");
         }
         else
         {
             Time.timeScale = 1f;
             mGameState = GameState.playing;
             Debug.Log("Game Playing");
         }
     }
 
     void GameMainMenu()
     {
         
         if (Input.anyKeyDown)
         {
             Application.LoadLevel(1);
             mGameState = GameState.playing;
         }
     }
 
     public static Game_Manager Instance
     {
         get
         {
             if (thisInstance == null)
             {
                 thisInstance = new GameObject("MySingleton").AddComponent<Game_Manager>();
             }
 
             return thisInstance;
         }
     }
 
     public void OnApplicationQuit()
     {
         thisInstance = null;
     }
 }


   

 // UI_Manager
 
 using UnityEngine;
 using System.Collections;
 
 public class UI_Manager : MonoBehaviour {
 
     // Use this for initialization
     void Start () {
         
     }
     
     void OnGUI()
     {
 
     }
 
     void Update()
     {
 
     }
 
     public void GamePauseGUI()
     {
         Debug.Log("Game Paused GUI");
     }
 }

Answer 1

My guess is that it is comming from this line:

 mUI.GamePauseGUI();

Unity does not automatically connect references except for built in accessors such as .transform. You need to manually reference the UI_Manager GameObject in order to use it. This can be done a number of ways, here's an example.

 public class Game_Manager : MonoBehaviour
 {
     private static Game_Manager thisInstance;
     private static GameState mGameState;
     //-------------------------
     private UI_Manager mUI;
     private UI_Manager MUI {
         get {
             if(mUI == null) {
                  mUI = (UI_Manager)FindObjectOfType(typeof(UI_Manager));
                   //^ this is the important line.
             }
             return mUI;
         }
     }
     //-------------------------
   
     public void GamePause() { /*use the property MUI to call your methods*/ }
 }

The important part of the above example is mUI = (UI_Manager)FindObjectOfType(typeof(UI_Manager));. The method finds an object of the given type in the scene and returns it. You need to cast it to its derived type though 95% of the time before you actually use it.

Answer 2

Answer by AaronG · Jun 11, 2011 at 05:10 PM

Thanks. Works perfectly!

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Peter G · Jun 11, 2011 at 06:03 PM 0

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$$anonymous$$ake sure to mark it the correct answer then. A checkmark outline should show up under the votes for my answer that you need to click on.

How do I call methods from other scripts using C#?

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