Delay creation of MAVLinkDecoder until it is needed

Helps battery life

src/ui/MainWindow.cc

@@ -108,10 +108,11 @@ void MainWindow::deleteInstance(void)
 ///         by MainWindow::_create method. Hence no other code should have access to
 ///         constructor.
 MainWindow::MainWindow()
-    : _lowPowerMode(false)
-    , _showStatusBar(false)
-    , _mainQmlWidgetHolder(NULL)
-    , _forceClose(false)
+    : _mavlinkDecoder       (NULL)
+    , _lowPowerMode         (false)
+    , _showStatusBar        (false)
+    , _mainQmlWidgetHolder  (NULL)
+    , _forceClose           (false)
 {
     _instance = this;
 
@@ -272,10 +273,13 @@ MainWindow::MainWindow()
 
 MainWindow::~MainWindow()
 {
-    // Enforce thread-safe shutdown of the mavlink decoder
-    mavlinkDecoder->finish();
-    mavlinkDecoder->wait(1000);
-    mavlinkDecoder->deleteLater();
+    if (_mavlinkDecoder) {
+        // Enforce thread-safe shutdown of the mavlink decoder
+        _mavlinkDecoder->finish();
+        _mavlinkDecoder->wait(1000);
+        _mavlinkDecoder->deleteLater();
+        _mavlinkDecoder = NULL;
+    }
 
     // This needs to happen before we get into the QWidget dtor
     // otherwise  the QML engine reads freed data and tries to
@@ -290,12 +294,18 @@ QString MainWindow::_getWindowGeometryKey()
 }
 
 #ifndef __mobile__
-void MainWindow::_buildCommonWidgets(void)
+MAVLinkDecoder* MainWindow::_mavLinkDecoderInstance(void)
 {
-    // Add generic MAVLink decoder
-    mavlinkDecoder = new MAVLinkDecoder(qgcApp()->toolbox()->mavlinkProtocol());
-    connect(mavlinkDecoder.data(), &MAVLinkDecoder::valueChanged, this, &MainWindow::valueChanged);
+    if (_mavlinkDecoder) {
+        _mavlinkDecoder = new MAVLinkDecoder(qgcApp()->toolbox()->mavlinkProtocol());
+        connect(_mavlinkDecoder, &MAVLinkDecoder::valueChanged, this, &MainWindow::valueChanged);
+    }
 
+    return _mavlinkDecoder;
+}
+
+void MainWindow::_buildCommonWidgets(void)
+{
     // Log player
     // TODO: Make this optional with a preferences setting or under a "View" menu
     logPlayer = new QGCMAVLinkLogPlayer(statusBar());
@@ -363,7 +373,7 @@ bool MainWindow::_createInnerDockWidget(const QString& widgetName)
                 widget = new HILDockWidget(widgetName, action, this);
                 break;
             case ANALYZE:
-                widget = new Linecharts(widgetName, action, mavlinkDecoder, this);
+                widget = new Linecharts(widgetName, action, _mavLinkDecoderInstance(), this);
                 break;
         }
         if(widget) {

src/ui/MainWindow.h

@@ -127,7 +127,6 @@ protected:
 
     QSettings settings;
 
-    QPointer<MAVLinkDecoder> mavlinkDecoder;
     QGCMAVLinkLogPlayer* logPlayer;
 #ifdef QGC_MOUSE_ENABLED_WIN
     /** @brief 3d Mouse support (WIN only) */
@@ -181,7 +180,9 @@ private:
     void _showDockWidget(const QString &name, bool show);
     void _loadVisibleWidgetsSettings(void);
     void _storeVisibleWidgetsSettings(void);
+    MAVLinkDecoder* _mavLinkDecoderInstance(void);
 
+    MAVLinkDecoder*         _mavlinkDecoder;
     bool                    _lowPowerMode;           ///< If enabled, QGC reduces the update rates of all widgets
     bool                    _showStatusBar;
     QVBoxLayout*            _centralLayout;