Fix BLE connection setup on Android 12+

Author: dv1

app/src/main/java/org/asteroidos/sync/asteroid/AsteroidBleManager.java

@@ -79,6 +79,10 @@ public static class BatteryLevelEvent {
         public int battery = 0;
     }
 
+    public final void readCharacteristics() {
+        readCharacteristic(batteryCharacteristic).with(((device, data) -> setBatteryLevel(data))).enqueue();
+    }
+
     private abstract class AsteroidBleManagerGattCallback extends BleManagerGattCallback {
 
         /* It is a constraint of the Bluetooth library that it is required to initialize
@@ -119,7 +123,7 @@ public final boolean isRequiredServiceSupported(@NonNull final BluetoothGatt gat
                     BluetoothGattCharacteristic characteristic1 = bluetoothGattService.getCharacteristic(characteristic);
                     removeNotificationCallback(characteristic1);
                     setNotificationCallback(characteristic1).with((device, data) -> callback.call(data.getValue()));
-                    enableNotifications(characteristic1).with((device, data) -> callback.call(data.getValue())).enqueue();
+                    enableNotifications(characteristic1).enqueue();
                 });
             }
 
@@ -138,7 +142,14 @@ protected final void initialize() {
                     .enqueue();
 
             setNotificationCallback(batteryCharacteristic).with(((device, data) -> setBatteryLevel(data)));
-            readCharacteristic(batteryCharacteristic).with(((device, data) -> setBatteryLevel(data))).enqueue();
+	    // Do not call readCharacteristic(batteryCharacteristic) here.
+	    // Otherwise, on Android 12 and later, the BLE bond to the watch
+	    // is lost, and communication no longer works. Arguably, reading
+	    // and writing should not be done in initialize(), since it is
+	    // part of the BLE manager's connect() request. Instead, do those
+	    // IO operations _after_ that request finishes (-> read the
+	    // characteristic in the SynchronizationService class, which is
+	    // where the BLE manager's connect() function is called).
             enableNotifications(batteryCharacteristic).enqueue();
 
             // Let all services know that we are connected.

app/src/main/java/org/asteroidos/sync/services/SynchronizationService.java

@@ -102,9 +102,15 @@ final void handleConnect() {
             device.createBond();
             mBleMngr.connect(device)
                     .useAutoConnect(true)
-                    .timeout(100000)
+                    .timeout(100 * 1000)
                     .retry(3, 200)
-                    .done(device1 -> Log.d(TAG, "Connected to " + device1.getName()))
+                    .done(device1 -> {
+                        Log.d(TAG, "Connected to " + device1.getName());
+			// Now we read the current values of the GATT characteristics,
+			// _after_ the connection has been fully established, to avoid
+			// connection failures on Android 12 and later.
+                        mBleMngr.readCharacteristics();
+                    })
                     .fail((device2, error) -> Log.e(TAG, "Failed to connect to " + device.getName() +
                             " with error code: " + error))
                     .enqueue();