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When your application is installed, Google Play Services downloads libraries to the device in order to detect QR codes. If another app already uses QR code detection on the device, the library won’t be downloaded again. Under certain circumstances (e.g.for example, the user isn't online, slow connection, or lack of sufficient storage space), the libraries aren’t ready at the time your app starts the camera screen and QR code detection is silently disabled until the next time the camera screen starts.
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