Improve Fact placeholder String support

Implemented Fact::placeholderString to centralize the placeholder String
generation logic and take into account the number of decimal places.
Changed various hardcoded fallback Strings in QML for consistency with
the new placeholder String format.

Author: rubenp02

src/FactSystem/Fact.cc

@@ -322,15 +322,7 @@ QStringList Fact::selectedBitmaskStrings() const
 QString Fact::_variantToString(const QVariant &variant, int decimalPlaces) const
 {
     if (!variant.isValid()) {
-        switch (type()) {
-        case FactMetaData::valueTypeFloat:
-        case FactMetaData::valueTypeDouble:
-            return QStringLiteral("--.--");
-        case FactMetaData::valueTypeElapsedTimeInSeconds:
-            return QStringLiteral("--:--:--");
-        default:
-            return QStringLiteral("-");
-        }
+        return invalidValueString(decimalPlaces);
     }
 
     QString valueString;
@@ -348,7 +340,7 @@ QString Fact::_variantToString(const QVariant &variant, int decimalPlaces) const
     {
         const float fValue = variant.toFloat();
         if (qIsNaN(fValue)) {
-            valueString = QStringLiteral("--.--");
+            valueString = invalidValueString(decimalPlaces);
         } else {
             valueString = QStringLiteral("%1").arg(fValue, 0, 'f', decimalPlaces);
             stripNegativeZero(valueString);
@@ -359,7 +351,7 @@ QString Fact::_variantToString(const QVariant &variant, int decimalPlaces) const
     {
         const double dValue = variant.toDouble();
         if (qIsNaN(dValue)) {
-            valueString = QStringLiteral("--.--");
+            valueString = invalidValueString(decimalPlaces);
         } else {
             valueString = QStringLiteral("%1").arg(dValue, 0, 'f', decimalPlaces);
             stripNegativeZero(valueString);
@@ -373,7 +365,7 @@ QString Fact::_variantToString(const QVariant &variant, int decimalPlaces) const
     {
         const double dValue = variant.toDouble();
         if (qIsNaN(dValue)) {
-            valueString = QStringLiteral("--:--:--");
+            valueString = invalidValueString(decimalPlaces);
         } else {
             QTime time(0, 0, 0, 0);
             time = time.addSecs(dValue);
@@ -389,6 +381,22 @@ QString Fact::_variantToString(const QVariant &variant, int decimalPlaces) const
     return valueString;
 }
 
+QString Fact::invalidValueString(int decimalPlaces) const {
+    switch (type()) {
+    case FactMetaData::valueTypeFloat:
+    case FactMetaData::valueTypeDouble:
+        if (decimalPlaces <= 0) {
+            return QStringLiteral("--");
+        }
+        return QStringLiteral("--.") +
+               QString(decimalPlaces, QLatin1Char('-'));
+    case FactMetaData::valueTypeElapsedTimeInSeconds:
+        return QStringLiteral("--:--:--");
+    default:
+        return QStringLiteral("--");
+    }
+}
+
 QString Fact::rawValueStringFullPrecision() const
 {
     return _variantToString(rawValue(), 18);

src/FactSystem/Fact.h

@@ -56,6 +56,7 @@ class Fact : public QObject
     Q_PROPERTY(QVariant     value                   READ cookedValue                WRITE setCookedValue        NOTIFY valueChanged)
     Q_PROPERTY(QVariant     rawValue                READ rawValue                   WRITE setRawValue           NOTIFY rawValueChanged)
     Q_PROPERTY(bool         valueEqualsDefault      READ valueEqualsDefault                                     NOTIFY valueChanged)
+    Q_PROPERTY(QString      invalidValueString      READ invalidValueString                                     CONSTANT)
     Q_PROPERTY(QString      valueString             READ cookedValueString                                      NOTIFY valueChanged)
     Q_PROPERTY(QString      enumOrValueString       READ enumOrValueString                                      NOTIFY valueChanged)
     Q_PROPERTY(double       increment               READ cookedIncrement                                        CONSTANT)
@@ -116,6 +117,8 @@ class Fact : public QObject
     FactMetaData::ValueType_t type() const { return _type; }
     QString cookedUnits() const;
     QString rawUnits() const;
+    QString invalidValueString(int decimalPlaces) const;
+    QString invalidValueString() const { return invalidValueString(decimalPlaces()); }
     QString rawValueString() const;
     QString cookedValueString() const;
     bool valueEqualsDefault() const;

src/QmlControls/InstrumentValueValue.qml

@@ -43,7 +43,7 @@ ColumnLayout {
             if (instrumentValueData.fact) {
                 return instrumentValueData.fact.enumOrValueString + (instrumentValueData.showUnits ? " " + instrumentValueData.fact.units : "")
             } else {
-                return qsTr("--.--")
+                return qsTr("--")
             }
         }
     }

src/UI/toolbar/EscIndicatorPage.qml

@@ -20,7 +20,7 @@ ToolIndicatorPage {
 
     property var    activeVehicle:  QGroundControl.multiVehicleManager.activeVehicle
     property string na:             qsTr("N/A", "No data to display")
-    property string valueNA:        qsTr("--.--", "No data to display")
+    property string valueNA:        qsTr("--", "No data to display")
 
     property var    _escs:          activeVehicle ? activeVehicle.escs : null
     property int    _onlineBitmask: _escs ? _escs.get(0).info.rawValue : 0