One of the coolest new features coming in Android N is the ability to directly reply to messages and emails from the notification bar. Here's how you can reply to notifications right now in Android Lollipop or Marshmallow. Also see: How to direct reply in Android N.
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How to directly reply to notifications in Android
To get started you'll need to download and install the free quickReply app from Google Play. Launch the app, accept the licence agreement, then tap on 'Please Activate quickReply'.
Under Notification access slide on the toggle next to quickReply to give it access to your notifications. You'll be asked whether you're sure you want to do that, so click Ok.
Launch quickReply and open the Settings menu. You'll notice that a lot of what's available here is restricted to the Pro version, but one thing you can do is configure which apps get quickReply access. Tap App settings, then deselect any apps you don't want to be associated with quickReply. Also see: Best Android phones 2016 UK.
When you next get a message via a supported application (such as WhatsApp, shown here), you'll find new options for Reply, Direct and Read. Tap Reply, write your response and hit the send button, all without opening the app. (Alternatively choose Direct for preset responses 'Yes', 'No' and 'Ok'.)
Supported apps include WhatsApp, Telegram, Threema, Skype, Line, WeChat, Kik, EvolveSms, YAATA, Textra, ChompSms, Hangouts, Handcent SMS and others. WhatsApp, Telegram, Threema, Skype, WeChat, Kik and EvolveSms also support the Mark As Read feature. Also see: How to read a WhatsApp message without the sender knowing.
We did find quickReply a little bit buggy (it is still in beta admittedly) in that it kept showing us the past few notifications each time we got a new one, but if you can put up with that it's a pretty cool app to have.