Which correct flag of autoConnect in connectGatt of BLE?

Solution 1:

"Direct connect" is the opposite to "auto connect", so if you set the autoConnect parameter to false you get a "direct connect". Note that doing a "mBluetoothGatt.connect()" will also use auto connect.

Beware of https://code.google.com/p/android/issues/detail?id=69834 which is a bug affecting older versions of Android which might make your auto connections to be direct connections instead. This can be worked around with reflection.

There are a few non-documented differences between direct and auto connect:

Direct connect is a connection attempt with a 30 seconds timeout. It will suspend all current auto connects while the direct connect is in progress. If there already is a direct connect pending, the last direct connect will not be executed immediately but rather be queued up and start when the previous has finished.

With auto connect you can have multiple pending connections at the same time and they will never time out (until explicitly aborted or until Bluetooth is turned off).

If the connection was established through an auto connect, Android will automatically try to reconnect to the remote device when it gets disconnected until you manually call disconnect() or close(). Once a connection established through direct connect disconnects, no attempt is made to reconnect to the remote device.

Direct connect has a different scan interval and scan window at a higher duty than auto connect, meaning it will dedicate more radio time to listen for connectable advertisements for the remote device, i.e. the connection will be established faster.

NEW CHANGE IN ANDROID 10

Since Android 10, the direct connect queue is removed and will not temporarily pause auto connects any more. This is because direct connect now uses the white list just like auto connects. The scan window/interval is improved while a direct connect is ongoing.