模仿拍完照的閃現效果

self.view.alpha = 0.0;
                                                                    [UIView animateWithDuration: 0.5
                                                                                     animations: ^{
                                                                                         self.view.alpha = 1.0;
                                                                                     }
                                                                                     completion: ^(BOOL finished) {
                                                                                     }
                                                                     ];