IPhone : Not able to understand iOS System UIPasteboard

i am working on custom emoji keyboard it is an keyboard extension and problem is that on clicking button i need to copy image in pasteboard and paste it into another app . i have used these code but not able to copy image into pasteboard

-code in .h file

    UIPasteboard *pasteboard_img;

-code in viewDidLoad()

    pasteboard_img = [UIPasteboard generalPasteboard];

-code in method which is call when button is pressed on keyboard

    [pasteboard_img setImage:[UIImage imageNamed:[array_image objectAtIndex:sender.tag]]];

~ where array_image is array with image name.