title: How to pair via bluetooth on android automatically?
body: <p>I hope I could pair and connect with a known bluetooth device automatically.
  My phone acts as the master part, while the device acts as the slave part.</p>
  
  <p>I already know the slave device's Mac address and pin code.</p>
  
  <p>How can I connect with the device with already-known MAC address and the pin code programmatically? which means there is no pairing UI.</p>
  
  <p>Thanks.</p>