Purple Rain is unique film; perhaps half the movie's length consists of live performances of Prince playing the songs from the soundtrack. And even when Prince isn't shown performing on stage, much of the rest of the movie is filled up with extended musical montages that are cut like music videos. In a sense, the film plays like a series of music videos, just strung together into a story. Despite (or because of) its experimental nature, Purple Rain proved to be popular with audiences, raking in almost ten times as much in box office sales ($67 million) as it had cost to produce ($7 million). It was the eleventh highest-grossing film of 1984 in the United States. Its soundtrack album (which included not only "When Doves Cry" but the additional hits "Let's Go Crazy," "Purple Rain," and "I Would Die 4 U") sold an additional 14 million copies and is regularly ranked among the greatest pop albums of all time. Purple Rain (the movie and the album) cemented Prince's reputation as one of the dominant pop-cultural forces of his generation.
"When Doves Cry" was written for a particular sequence in the movie, illustrating a moment when the Kid (the character played by Prince) has to choose which path his life will follow. Will his relationship with Apollonia be one of pure love and playful sex, or will his jealousy of her own musical career lead to uncontrollable anger and the nightmare of domestic abuse? Will he follow the tragic path laid out by his violent father, or will he find his own way? Will he find a way to reconcile with his band, allowing him to succeed as a musician, or will his pride lead to a breakup?
You'll have to watch the movie to find out.