This Android app registers an input method that you can use like any other Android keyboard.
However, instead of keys it shows a camera window. Whenever a barcode (1D codes, QR, DataMatrix, …)
is inside the camera view, the barcode content will be inserted into the current text fields.

Similar apps already exist, but show lots of ads, require in-app purchases to remove ads, and
have the risk of leaking your data. This app is free and open source and does not even request
permission to connect to the internet from the operating system. You can therefore fully trust
this app not to send your QR code data somewhere.