Next and previous button in NGUI

 I have two buttons on both sides of simple texture.
 Only three types of image i have. that i kept in a array.
 while clicking on next button, image name print.
 but previous function not working properly .
 i declared in UIButtonMessage.cs
     public string[] imageArray = {"c1_ipad", "c2_ipad", "c3_ipad"};
     public int arrayKey;
 and function 
     void Next() 
     {
         if(arrayKey!=2)
         {
             arrayKey = arrayKey + 1;
         }
         print(imageArray[arrayKey]);    
     }
 
     void Previous () 
     { print(arrayKey);
         
         if(arrayKey!=0)
         {
             arrayKey = arrayKey - 1;
         }
         print(arrayKey);
         print(imageArray[arrayKey]);
 
     }    
  but arraykey changed in one function , not getting in another function.
  Please help me solve to this issue.

  i am very new to NGUI. how can i show image in simple texture.
 
 Thanks in advance