more bug fixes.

Author: m4gr3d

ServiceApp/src/org/droidplanner/services/android/communication/connection/usb/UsbCDCConnection.java

@@ -19,6 +19,8 @@
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicReference;
 
+import timber.log.Timber;
+
 class UsbCDCConnection extends UsbConnection.UsbConnectionImpl {
     private static final String TAG = UsbCDCConnection.class.getSimpleName();
     private static final String ACTION_USB_PERMISSION = "com.android.example.USB_PERMISSION";
@@ -78,7 +80,11 @@ private void registerUsbPermissionBroadcastReceiver() {
     }
 
     private void unregisterUsbPermissionBroadcastReceiver() {
-        mContext.unregisterReceiver(broadcastReceiver);
+        try {
+            mContext.unregisterReceiver(broadcastReceiver);
+        }catch(IllegalArgumentException e){
+            Timber.e(e, "Receiver was not registered.");
+        }
     }
 
     private void removeWatchdog() {

ServiceApp/src/org/droidplanner/services/android/core/drone/DroneManager.java

@@ -521,6 +521,8 @@ private void handleCommandAck(msg_command_ack ack) {
     @Override
     public void notifyReceivedData(MAVLinkPacket packet) {
         MAVLinkMessage receivedMsg = packet.unpack();
+        if(receivedMsg == null)
+            return;
 
         if (receivedMsg.msgid == msg_command_ack.MAVLINK_MSG_ID_COMMAND_ACK) {
             final msg_command_ack commandAck = (msg_command_ack) receivedMsg;

ServiceApp/src/org/droidplanner/services/android/core/gcs/GCSHeartbeat.java

@@ -58,7 +58,7 @@ public GCSHeartbeat(MAVLinkClient mavClient, int freqHz) {
      *
      * @param active true to activate the heartbeat, false to deactivate it
      */
-    public void setActive(boolean active) {
+    public synchronized void setActive(boolean active) {
         if (active) {
             if (heartbeatExecutor == null || heartbeatExecutor.isShutdown()) {
                 heartbeatExecutor = Executors.newSingleThreadScheduledExecutor();