Android Tutorial Using POP3 to communicate with Android devices

Many developers face the challenge of sending data to remote devices. These devices can be at times offline, sleeping or without proper network coverage.
There are several possible solutions. The device can contact a web server which will return the required data.
Another solution is to use Google push notification framework.
Here I want to present a third solution which doesn't require any custom server and is pretty simple.
Using the Net library a device can connect to a mail server and download the mail messages.
This solution can fit very well in many cases and is very simple to manage. Mail servers are very common and are easy to work with.
All you need is an email service that supports POP3. Gmail is one such service.

The POP3 object from the Net library returns the raw messages as strings.
Additional work is required to get the message fields and especially to extract attachments from the messages.
MailParser code module is included in the attached project.
MailParser parses the messages, saves the attachments and returns Messages objects which hold the various fields.

MailParser cannot be used as a real mail client. There are many possible formats and encodings. MailParser can handle simple formats with zero or more attachments.

Parsing a message is done by calling:
B4X:
      Dim m As Message
      m = MailParser.ParseMail(MessageText, File.DirRootExternal)
The first parameter is the raw message and the second is the folder that the attachments will be saved to.

MailParser requires StringUtils library for the base64 decoding.
 

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