Sometimes it is stripped out by device manufacturers, but if you have a Pixel or Nexus thats running Nougat, then youre in luck.
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GOOGLE PIXEL SYSTEM UI TUNER INSTALL
Since Lock screen shortcuts are hidden under System UI tuner menu, it is possible that they will either graduate to a full blown feature by the time the final version of the OS is released. System UI Tuner has been sitting in Android for a number of versions. >Download and install SystemUI Tuner from the Google Play Store. Then, head over to Settings -> System -> System UI Tuner -> Lock screen to customise the lock screen shortcut. When you leave the button, you should get a toast notification saying that the System UI tuner menu has been enabled. If you are running the Android O developer preview on your Pixel or Nexus device, you can bring up the hidden System UI tuner menu by long pressing the cog Settings icon in the Quick Settings menu for a few seconds. The chances of that happening seem pretty unlikely to me, though. Since the feature is buried under the System UI tuner, it is possible that Google will remove it from the final version of the OS. If you want, you can set a shortcut to jump directly to a particular section of the Settings menu, open a new Chrome tab, do a quick Google search, launch the selfie camera app, and more.This feature has long been available on custom ROMs and Google is finally getting around to natively adding it to Android with O. You are not limited to setting the shortcut to open a particular app. The feature is pretty simple and essentially lets you set custom shortcuts for the right and left shortcuts on the lock screen. In order for this system to work correctly with a wide range of apps, app developers must adhere to the basic requirements recommended and outlined by Google. This works the same as Google's own method of launching the UI Tuner in. This application is simply a shortcut to launch the hidden System UI Tuner menu without the need to use ADB or install a custom launcher. The first Developer Preview of Android O is no different and hides some interesting customisation options under System UI tuner, with one of them being the ability to customise the lock screen shortcuts. The option to launch System UI Tuner in Android version 9 and newer has been removed by Google, but the utility does still exist. As a quick reminder: if you remove System UI Tuner, you cant use Night mode, and any default status bar items you may have toggled off will be turned back on. Since Marshmallow, Google has used the hidden System UI Tuner menu to hide useful customisation options in the OS. Only thing is I cannot enter the system UI tuner at all, I have tried holding down the cog at the top of the screen but this. If you added System UI Tuner to your Settings poked around, and decided you dont need any of this awesomeness, you can take them back off the visible menu in Settings quite easily.