c# - Error when play is clicked:NullReferenceException: Object reference not set to an instance of an object -

i pretty new c# , unity,so question basic. has bugged me long, couldn't on after research on internet.

anyway, here question, have got error

nullreferenceexception: object reference not set instance of object achievementbutton.click()(at assets/scripts/achievementsystem/achievementbutton.cs:25) achievementmanager.start()(at assets/scripts/achievementsystem/achievementmanager.cs:30)

when clicked on play or when click button view list of achievements.

achievementmanager script:

using unityengine; using system.collections; using unityengine.ui;  public class achievemenetmanager : monobehaviour {       public gameobject achievementprefab;      public sprite[] sprites;      public achievementbutton activebutton;       public scrollrect scrollrect;       // use initialization      void start ()     {         //here error logged         activebutton = gameobject.find("streakbtn").getcomponent<achievementbutton>();         createachievement("streak","testtitle","this description",3,0);          activebutton.click();      }      // update called once per frame     void update () {      }      public void createachievement(string category,string title,string description,int points, int spriteindex)     {         gameobject achievement = (gameobject)instantiate(achievementprefab);         setachievementinfo(category, achievement,title,description,points,spriteindex);     }      public void setachievementinfo(string category, gameobject achievement, string title, string description, int points, int spriteindex)     {         achievement.transform.setparent(gameobject.find(category).transform);         achievement.transform.localscale = new vector3(1, 1, 1);         achievement.transform.localposition = new vector3(0, 0, 0);         achievement.transform.getchild(0).getcomponent<text>().text = title;         achievement.transform.getchild(1).getcomponent<text>().text = description;         achievement.transform.getchild(2).getcomponent<text>().text = points.tostring();         achievement.transform.getchild(3).getcomponent<image>().sprite = sprites[spriteindex];     }     public void changecategery(gameobject button)     {         achievementbutton achievementbutton = button.getcomponent<achievementbutton>();          scrollrect.content = achievementbutton.achievementlist.getcomponent<recttransform>();          achievementbutton.click();         activebutton.click();          activebutton = achievementbutton;         }  } 

achievementbutton script:

using unityengine; using system.collections; using unityengine.ui;  public class achievementbutton : monobehaviour  {       public gameobject achievementlist;      public sprite neutral, highlight;      private image sprite;      void awake()     {         sprite = getcomponent<image>();      }        public void click()     {          //here error logged          if(sprite.sprite == neutral)         {             sprite.sprite = highlight;             achievementlist.setactive(true);          }          else         {             sprite.sprite = neutral;             achievementlist.setactive(false);         }     } } 

your awake() method starts lowercase, while should start uppercase: void awake()

adjust awake method this:

void awake() {     sprite = getcomponent<image>();     debug.log("awake has been called, sprite " + sprite);     debug.log("neutral " + neutral);     debug.log("highlight " + highlight); } 

to see whether method gets called @ , whether 3 variables (sprite, neutral, highlight) defined (they must not null).

you can see output of debug.log() in console, can found in unity when click on menu item view -> console. use debug.log() see what's going on in scripts.

if neutral , highlight variables null in awake, need assign them manually via inspector, i.e. drag , drop sprites them achievementbutton game object in editor.