模态全屏模式，实现半透明效果

self.view.window.rootViewController.modalPresentationStyle = UIModalPresentationCurrentContext; //半透明

        BiaoQianViewController *biaoQianVC = [[BiaoQianViewController alloc] init];

        biaoQianVC.modalPresentationStyle = UIModalPresentationOverFullScreen;

        biaoQianVC.view.frame = self.view.frame;

        [self presentViewController:biaoQianVC animated:YES completion:nil];