Try TTF upper case instead of ttf in all of your code.

The Options are:

1. Try TTF upper case instead of ttf in all of your code - in case your original file has TTF suffix, because android is case sensitive.

2. In build.gradle file under your android module make sure that:

   assets.srcDirs = ['assets']

And not:

assets.srcDirs = ['assetManager']

In another words make sure its your android assets folder. this one worked for me. then clean build project, and uninstall old app from android device.