Making onscreen D-pad for mobile game

Im having a complete mental block on how i would go about making an onscreen D-pad for a 3d game. I believe i can use the new UI buttons on an image of a dpad then when they are held down the character will move in that position. But its not working, don't know what to write to get it to work. I can currently only get the button to pressed once on the down, but no holding.