android 设置全屏，导航栏透明

在onCreate（）中
setContentView之后

if (Build.VERSION.SDK_INT >= 21) {
            val decorView = window.decorView
            val option = (View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION
                    or View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
                    or View.SYSTEM_UI_FLAG_LAYOUT_STABLE)
            decorView.systemUiVisibility = option
            window.navigationBarColor = Color.TRANSPARENT
            window.statusBarColor = Color.TRANSPARENT
        }
        supportActionBar?.hide()