timer issue at getting previous view

hi i am new to iPhone development. what i am doing is displaying 20 images as grid and each image t开发者_运维知识库reat as button,by selecting that image it will be displayed on image view "here what i needed is i using timer to get back to grid but there is [NSCFArray ObjectAtIndex]: index(4) beyond bounds(4) and application terminates" how can i slove this problem pls help me

Going on very little information here. My best guess is that your grid is 4x5, and you have inadvertently swapped your "x" and "y" variables, i.e. you are trying to access location [4] in an array that only goes from [0] to [3].