Important: For Marshmallow (Android 6), it is possible to disable the assist feature.
Follow below steps:
(1) goto "Settings > Apps > Advanced (the small gear icon) > Default Apps > Assists & voice input"
(2) select "none"
My thanks to robojumper for the above information.
The exact location of the settings may differ between Android version, for example, on Android 7, the settings is located at
"Settings > Apps > Advanced (top right gear icon) > Assist & voice input > Assist app"
So a little searching maybe necessary.
As of Jelly Bean, it is possible to quick launch an app (Google Now by default) by a swipe up gesture from the navigation bar, this feature can be annoying.
This app is developed to "disable" this feature. Actually the feature is not disabled, but instead launches this app that does nothing.
*** Important notes ***
This app does not provide a launch icon in the app drawer, so it is not possible to uninstall it in the conventional way.
Can use below methods to uninstall:
(1) Use an uninstaller app, there are many on Play Store, and AppWererabbit is a good choice.
(2) Goto "Settings > Apps > ALL", locate "SwipeLaunch Disabler", select to uninstall from App info screen.
This app may not be applicable to devices with a physical HOME button, mostly Samsung devices.
On devices with physical HOME button, long pressing the HOME button is equivalent to swipe launch action on buttonless devices, which maybe less prone to launching of Google Now by mistake.
The "semi-circle ring" on pre-Lollipop and "exploding circle" on Lollipop is animation prior to launching this app, therefore, out of control of this app.
The code is open source and available on github: https://github.com/HairyRobot/SwipeLaunchDisabler