Also move the resource management into DeviceSupport classes

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/AbstractBTDeviceSupport.java

@@ -11,6 +11,20 @@ public abstract class AbstractBTDeviceSupport extends AbstractDeviceSupport {
 
     protected abstract GBDeviceIoThread createDeviceIOThread();
     
+    @Override
+    public void dispose() {
+        // currently only one thread allowed
+        if (gbDeviceIOThread != null) {
+            gbDeviceIOThread.quit();
+            try {
+                gbDeviceIOThread.join();
+            } catch (InterruptedException e) {
+                e.printStackTrace();
+            }
+            gbDeviceIOThread = null;
+        }
+    }
+    
     public synchronized GBDeviceProtocol getDeviceProtocol() {
         if (gbDeviceProtocol == null) {
             gbDeviceProtocol = createDeviceProtocol();
@@ -26,7 +40,7 @@ public abstract class AbstractBTDeviceSupport extends AbstractDeviceSupport {
     }
     
     protected void sendToDevice(byte[] bytes) {
-        if (bytes != null) {
+        if (bytes != null && gbDeviceIOThread != null) {
             gbDeviceIOThread.write(bytes);
         }
     }

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/BluetoothCommunicationService.java

@@ -103,15 +103,8 @@ public class BluetoothCommunicationService extends Service {
                 sharedPrefs.edit().putString("last_device_address", btDeviceAddress).commit();
 
                 if (btDeviceAddress != null && !isConnected() && !isConnecting()) {
-                    // currently only one thread allowed
-                    if (mGBDeviceIoThread != null) {
-                        mGBDeviceIoThread.quit();
-                        try {
-                            mGBDeviceIoThread.join();
-                        } catch (InterruptedException e) {
-                            e.printStackTrace();
-                        }
-
+                    if (mDeviceSupport != null) {
+                        mDeviceSupport.dispose();
                     }
                     BluetoothDevice btDevice = mBtAdapter.getRemoteDevice(btDeviceAddress);
                     if (btDevice != null) {
@@ -201,13 +194,8 @@ public class BluetoothCommunicationService extends Service {
 
         GB.setReceiversEnableState(false, this); // disable BroadcastReceivers
 
-        if (mGBDeviceIoThread != null) {
-            try {
-                mGBDeviceIoThread.quit();
-                mGBDeviceIoThread.join();
-            } catch (InterruptedException e) {
-                e.printStackTrace();
-            }
+        if (mDeviceSupport != null) {
+            mDeviceSupport.dispose();
         }
         NotificationManager nm = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
         nm.cancel(GB.NOTIFICATION_ID); // need to do this because the updated notification wont be cancelled when service stops

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/DeviceSupport.java

@@ -13,4 +13,6 @@ public interface DeviceSupport extends EventHandler {
     public BluetoothAdapter getBluetoothAdapter();
     
     public Context getContext();
+
+    public void dispose();
 }