Review iterations over QStrings

There are many ways of iterating over lists in C++/Qt.
In the specific case of QStrings, it is known [1] that using
foreach with const references avoids the creation of new
QString objects in each iteration, reducing the time consumed
by the loops.

[1] https://blog.qt.io/blog/2009/01/23/iterating-efficiently/



Signed-off-by: Anselmo L. S. Melo <anselmo.melo@intel.com>

src/qgcunittest/RadioConfigTest.cc

@@ -407,7 +407,7 @@ void RadioConfigTest::_fullCalibrationWorker(MAV_AUTOPILOT firmwareType)
                     QStringList switchList;
                     switchList << "RC_MAP_MODE_SW" << "RC_MAP_LOITER_SW" << "RC_MAP_RETURN_SW" << "RC_MAP_POSCTL_SW" << "RC_MAP_ACRO_SW";
 
-                    foreach (QString switchParam, switchList) {
+                    foreach (const QString &switchParam, switchList) {
                         Q_ASSERT(_autopilot->getParameterFact(FactSystem::defaultComponentId, switchParam)->rawValue().toInt() != channel + 1);
                     }
                 }

src/ui/linechart/LinechartPlot.cc

@@ -183,7 +183,7 @@ void LinechartPlot::setActive(bool active)
 
 void LinechartPlot::removeTimedOutCurves()
 {
-    foreach(QString key, lastUpdate.keys())
+    foreach(const QString &key, lastUpdate.keys())
     {
         quint64 time = lastUpdate.value(key);
         if (QGC::groundTimeMilliseconds() - time > 10000)
@@ -499,7 +499,7 @@ bool LinechartPlot::isVisible(QString id)
 bool LinechartPlot::anyCurveVisible()
 {
     bool visible = false;
-    foreach (QString key, curves.keys())
+    foreach (const QString &key, curves.keys())
     {
         if (curves.value(key)->isVisible())
         {

src/ui/linechart/LinechartWidget.cc

@@ -673,7 +673,7 @@ void LinechartWidget::removeCurve(QString curve)
 void LinechartWidget::recolor()
 {
     activePlot->styleChanged(qgcApp()->styleIsDark());
-    foreach (QString key, colorIcons.keys())
+    foreach (const QString &key, colorIcons.keys())
     {
         QWidget* colorIcon = colorIcons.value(key, 0);
         if (colorIcon && !colorIcon->styleSheet().isEmpty())
@@ -713,7 +713,7 @@ void LinechartWidget::filterCurves(const QString &filter)
     {
         /* Hide Elements which do not match the filter pattern */
         QStringMatcher stringMatcher(filter, Qt::CaseInsensitive);
-        foreach (QString key, colorIcons.keys())
+        foreach (const QString &key, colorIcons.keys())
         {
             if (stringMatcher.indexIn(key) < 0)
             {
@@ -728,7 +728,7 @@ void LinechartWidget::filterCurves(const QString &filter)
     else
     {
         /* Show all Elements */
-        foreach (QString key, colorIcons.keys())
+        foreach (const QString &key, colorIcons.keys())
         {
             filterCurve(key, true);
         }
@@ -796,7 +796,7 @@ QString LinechartWidget::getCurveName(const QString& key, bool shortEnabled)
 
 void LinechartWidget::setShortNames(bool enable)
 {
-    foreach (QString key, curveNames.keys())
+    foreach (const QString &key, curveNames.keys())
     {
         curveNameLabels.value(key)->setText(getCurveName(key, enable));
     }