Why "Buttons in button bars should be borderless" in Android API Level 15?

Solution 1:

The borderless buttons are for cohesiveness of design throughout the android platform. It's recommended you follow the guidelines so that the user feels that your app is native and does not stick out like a sore thumb, but there are many cases where it just doesn't make sense, like if it makes your app look unprofessional. If that is the case, you may want to turn off the warning.

To turn off the warning, go to the project properties -> Android Lint Preferences. Search for "border" or "ButtonStyle" and change the severity to ignore on the bottom right.

You can also do this in Eclipse preferences for all projects.

For Android Studio Users:
File -> Settings -> Editor -> Inspections -> Android Lint. Search for "borderless" and uncheck or change the severity.

Solution 2:

Here is another simple way to get rid of it.

The compiler is trying to tell you to set the style of the button. So simply add the following style for the Android default borderless style and the error will be gone.

<Button
    ...
    style="?android:attr/borderlessButtonStyle"/>

Here is the proof