通过windowmanager在camera界面上显示内容

https://www.baidu.com/s?ie=UTF-8&wd=%E9%80%9A%E8%BF%87windowmanager%E5%9C%A8camera%E7%95%8C%E9%9D%A2%E4%B8%8A%E6%98%BE%E7%A4%BA%E5%86%85%E5%AE%B9

https://bbs.csdn.net/topics/391990009?page=1

WM.addView exception: Unable to add window — token null is not valid; is your activity running?

https://www.jianshu.com/p/4c5fafe08fa7