使用swift在AVAudioPlayer中恢复声音

I am trying to play a clip of sound that can be paused, resumed or stopped. My pause button works, and the action function for this button is shown below. However I cannot get my resume function to work. When I press the resume button no audio is played. I have read around online and the only tips I can find are to use the prepareToPlay() function and to set shortStartTimeDelay to a value greater than 0.0. I have tried both of these to no avail. I am trying to play a clip of sound that can be