App quit blur the foreground

Ideas:

1, will be launched into the background, screen capture image

2, adding to the image blur

3, after exiting the background display image blur on the window

4, App back to the front desk after not displayed

Note: The first time I actually do is UIVisualEffectView related practice, but the effect does not look good

Reproduced in: https: //www.jianshu.com/p/8a5a7fd7a64e