Use FactBinder to access facts from Qml

Passing parameters QVariantMap across C++ boundary was causing crashes
in Qt due to Qml array bugs. Referencing same Fact* across Qml boundary
in multiple QQuickWidgets caused jScript GC to crash.

qgroundcontrol.pro

@@ -774,6 +774,7 @@ INCLUDEPATH += \
 HEADERS += \
     src/FactSystem/FactSystem.h \
     src/FactSystem/Fact.h \
+    src/FactSystem/FactBinder.h \
     src/FactSystem/FactMetaData.h \
     src/FactSystem/FactValidator.h \
     src/FactSystem/FactLoader.h \
@@ -781,6 +782,7 @@ HEADERS += \
 SOURCES += \
     src/FactSystem/FactSystem.cc \
     src/FactSystem/Fact.cc \
+    src/FactSystem/FactBinder.cc \
     src/FactSystem/FactMetaData.cc \
     src/FactSystem/FactValidator.cc \
     src/FactSystem/FactLoader.cc \

src/AutoPilotPlugins/AutoPilotPlugin.cc

@@ -62,3 +62,13 @@ void AutoPilotPlugin::refreshParametersPrefix(const QString& paramPrefix)
         }
     }
 }
+
+bool AutoPilotPlugin::factExists(const QString& param)
+{
+    return parameters().contains(param);
+}
+
+Fact* AutoPilotPlugin::getFact(const QString& name)
+{
+    return parameters()[name].value<Fact*>();
+}

src/AutoPilotPlugins/AutoPilotPlugin.h

@@ -50,7 +50,6 @@ class AutoPilotPlugin : public QObject
 public:
     AutoPilotPlugin(UASInterface* uas, QObject* parent);
     
-    Q_PROPERTY(QVariantMap parameters READ parameters CONSTANT)
     Q_PROPERTY(QVariantList components READ components CONSTANT)
     Q_PROPERTY(QUrl setupBackgroundImage READ setupBackgroundImage CONSTANT)
     
@@ -62,6 +61,10 @@ public:
     
     // Request a refresh on all parameters that begin with the specified prefix
     Q_INVOKABLE void refreshParametersPrefix(const QString& paramPrefix);
+    
+    Q_INVOKABLE bool factExists(const QString& param);
+    
+    Fact* getFact(const QString& name);
 
     // Property accessors
     virtual const QVariantList& components(void) = 0;

src/AutoPilotPlugins/PX4/AirframeComponentSummary.qml

@@ -3,6 +3,7 @@ import QtQuick.Controls 1.2
 import QtQuick.Controls.Styles 1.2
 
 import QGroundControl.FactSystem 1.0
+import QGroundControl.FactControls 1.0
 import QGroundControl.Controls 1.0
 
 Column {
@@ -13,10 +14,10 @@ Column {
         width: parent.width
 
         QGCLabel { id: systemId; text: "System ID:" }
-        QGCLabel {
+        FactLabel {
             horizontalAlignment: Text.AlignRight
             width: parent.width - systemId.contentWidth
-            text: autopilot.parameters["MAV_SYS_ID"].value
+            fact: Fact { name: "MAV_SYS_ID" }
         }
     }
 
@@ -25,9 +26,10 @@ Column {
 
         QGCLabel { id: airframe; text: "Airframe:" }
         QGCLabel {
+            property Fact fact: Fact { name: "SYS_AUTOSTART" }
             horizontalAlignment: Text.AlignRight
             width: parent.width - airframe.contentWidth
-            text: autopilot.parameters["SYS_AUTOSTART"].value == 0 ? "Setup required" : autopilot.parameters["SYS_AUTOSTART"].value
+            text: fact.value == 0 ? "Setup required" : fact.value
         }
     }
 }

src/AutoPilotPlugins/PX4/FlightModesComponentSummary.qml

@@ -9,47 +9,51 @@ Column {
     anchors.fill: parent
     anchors.margins: 8
 
-    Row {
-        width: parent.width
-
-        QGCLabel { id: mode; text: "Mode switch:" }
-        QGCLabel {
-            horizontalAlignment: Text.AlignRight
-            width: parent.width - mode.contentWidth
-            text: autopilot.parameters["RC_MAP_MODE_SW"].value == 0 ? "Setup required" : autopilot.parameters["RC_MAP_MODE_SW"].value
+    Component {
+        id: component
+
+        Row {
+            width: parent.width
+
+            QGCLabel { id: label; text: labelText }
+            QGCLabel {
+                property Fact fact: Fact { name: factName }
+                horizontalAlignment: Text.AlignRight
+                width: parent.width - label.contentWidth
+                text: fact.value == 0 ? zeroText : fact.value
+            }
         }
     }
 
-    Row {
+    Loader {
+        property string labelText: "Mode switch:"
+        property string zeroText: "Setup required"
+        property string factName: "RC_MAP_MODE_SW"
         width: parent.width
-
-        QGCLabel { id: posctl; text: "Position Ctl switch:" }
-        QGCLabel {
-            horizontalAlignment: Text.AlignRight
-            width: parent.width - posctl.contentWidth
-            text: autopilot.parameters["RC_MAP_POSCTL_SW"].value == 0 ? "Disabled" : autopilot.parameters["RC_MAP_POSCTL_SW"].value
-        }
+        sourceComponent: component
     }
 
-    Row {
+    Loader {
+        property string labelText: "Position Ctl switch:"
+        property string zeroText: "Disabled"
+        property string factName: "RC_MAP_POSCTL_SW"
         width: parent.width
-
-        QGCLabel { id: loiter; text: "Loiter switch:" }
-        QGCLabel {
-            horizontalAlignment: Text.AlignRight
-            width: parent.width - loiter.contentWidth
-            text: autopilot.parameters["RC_MAP_LOITER_SW"].value == 0 ? "Disabled" : autopilot.parameters["RC_MAP_LOITER_SW"].value
-        }
+        sourceComponent: component
     }
 
-    Row {
+    Loader {
+        property string labelText: "Position Ctl switch:"
+        property string zeroText: "Disabled"
+        property string factName: "RC_MAP_LOITER_SW"
         width: parent.width
+        sourceComponent: component
+    }
 
-        QGCLabel { id: rtl; text: "Return switch:" }
-        QGCLabel {
-            horizontalAlignment: Text.AlignRight
-            width: parent.width - rtl.contentWidth
-            text: autopilot.parameters["RC_MAP_RETURN_SW"].value == 0 ? "Disabled" : autopilot.parameters["RC_MAP_RETURN_SW"].value
-        }
+    Loader {
+        property string labelText: "Return switch:"
+        property string zeroText: "Disabled"
+        property string factName: "RC_MAP_RETURN_SW"
+        width: parent.width
+        sourceComponent: component
     }
 }

src/AutoPilotPlugins/PX4/RadioComponentSummary.qml

@@ -9,80 +9,75 @@ Column {
     anchors.fill: parent
     anchors.margins: 8
 
-    Row {
-        width: parent.width
-
-        QGCLabel { id: roll; text: "Roll:" }
-        QGCLabel {
-            horizontalAlignment: Text.AlignRight
-            width: parent.width - roll.contentWidth
-            text: autopilot.parameters["RC_MAP_ROLL"].value == 0 ? "Setup required" : autopilot.parameters["RC_MAP_ROLL"].value
+    Component {
+        id: component
+
+        Row {
+            width: parent.width
+
+            QGCLabel { id: label; text: labelText }
+            QGCLabel {
+                Fact { id: fact; name: factName }
+                horizontalAlignment: Text.AlignRight
+                width: parent.width - label.contentWidth
+                text: fact.value == 0 ? zeroText : fact.value
+            }
         }
     }
 
-    Row {
+    Loader {
+        property string labelText: "Roll:"
+        property string zeroText: "Setup required"
+        property string factName: "RC_MAP_ROLL"
         width: parent.width
-
-        QGCLabel { id: pitch; text: "Pitch:" }
-        QGCLabel {
-            horizontalAlignment: Text.AlignRight
-            width: parent.width - pitch.contentWidth
-            text: autopilot.parameters["RC_MAP_PITCH"].value == 0 ? "Setup required" : autopilot.parameters["RC_MAP_PITCH"].value
-        }
+        sourceComponent: component
     }
 
-    Row {
+    Loader {
+        property string labelText: "Pitch:"
+        property string zeroText: "Setup required"
+        property string factName: "RC_MAP_PITCH"
         width: parent.width
-
-        QGCLabel { id: yaw; text: "Yaw:" }
-        QGCLabel {
-            horizontalAlignment: Text.AlignRight
-            width: parent.width - yaw.contentWidth
-            text: autopilot.parameters["RC_MAP_YAW"].value == 0 ? "Setup required" : autopilot.parameters["RC_MAP_YAW"].value
-        }
+        sourceComponent: component
     }
 
-    Row {
+    Loader {
+        property string labelText: "Yaw:"
+        property string zeroText: "Setup required"
+        property string factName: "RC_MAP_YAW"
         width: parent.width
-
-        QGCLabel { id: throttle; text: "Throttle:" }
-        QGCLabel {
-            horizontalAlignment: Text.AlignRight
-            width: parent.width - throttle.contentWidth
-            text: autopilot.parameters["RC_MAP_THROTTLE"].value == 0 ? "Setup required" : autopilot.parameters["RC_MAP_THROTTLE"].value
-        }
+        sourceComponent: component
     }
 
-    Row {
+    Loader {
+        property string labelText: "Throttle:"
+        property string zeroText: "Setup required"
+        property string factName: "RC_MAP_THROTTLE"
         width: parent.width
-
-        QGCLabel { id: flaps; text: "Flaps:" }
-        QGCLabel {
-            horizontalAlignment: Text.AlignRight
-            width: parent.width - flaps.contentWidth
-            text: autopilot.parameters["RC_MAP_FLAPS"].value == 0 ? "Disabled" : autopilot.parameters["RC_MAP_FLAPS"].value
-        }
+        sourceComponent: component
     }
 
-    Row {
+    Loader {
+        property string labelText: "Flaps:"
+        property string zeroText: "Disabled"
+        property string factName: "RC_MAP_FLAPS"
         width: parent.width
-
-        QGCLabel { id: aux1; text: "Aux1:" }
-        QGCLabel {
-            horizontalAlignment: Text.AlignRight
-            width: parent.width - aux1.contentWidth
-            text: autopilot.parameters["RC_MAP_AUX1"].value == 0 ? "Disabled" : autopilot.parameters["RC_MAP_AUX1"].value
-        }
+        sourceComponent: component
     }
 
-    Row {
+    Loader {
+        property string labelText: "Aux1:"
+        property string zeroText: "Disabled"
+        property string factName: "RC_MAP_AUX1"
         width: parent.width
+        sourceComponent: component
+    }
 
-        QGCLabel { id: aux2; text: "Aux2:" }
-        QGCLabel {
-            horizontalAlignment: Text.AlignRight
-            width: parent.width - aux2.contentWidth
-            text: autopilot.parameters["RC_MAP_AUX2"].value == 0 ? "Disabled" : autopilot.parameters["RC_MAP_AUX2"].value
-        }
+    Loader {
+        property string labelText: "Aux2:"
+        property string zeroText: "Disabled"
+        property string factName: "RC_MAP_AUX2"
+        width: parent.width
+        sourceComponent: component
     }
 }

src/AutoPilotPlugins/PX4/SafetyComponent.qml

@@ -61,7 +61,7 @@ Rectangle {
                     QGCLabel { text: "Return Home after"; anchors.baseline: rcLossField.baseline }
                     FactTextField {
                         id: rcLossField
-                        fact: autopilot.parameters["COM_RC_LOSS_T"]
+                        fact: Fact { name: "COM_RC_LOSS_T" }
                         showUnits: true
                     }
                 }
@@ -70,7 +70,7 @@ Rectangle {
                     spacing: 10
                     FactCheckBox {
                         id: telemetryTimeoutCheckbox
-                        fact: autopilot.parameters["COM_DL_LOSS_EN"]
+                        fact: Fact { name: "COM_DL_LOSS_EN" }
                         checkedValue: 1
                         uncheckedValue: 0
                         text: "Telemetry Signal Timeout"
@@ -80,7 +80,7 @@ Rectangle {
                     QGCLabel { text: "Return Home after"; anchors.baseline: telemetryLossField.baseline }
                     FactTextField {
                         id: telemetryLossField
-                        fact: autopilot.parameters["COM_DL_LOSS_T"];
+                        fact: Fact { name: "COM_DL_LOSS_T" }
                         showUnits: true
                         enabled: telemetryTimeoutCheckbox.checked
                     }
@@ -125,7 +125,7 @@ Rectangle {
                         QGCLabel { text: "Climb to altitude of" }
                         FactTextField {
                             id: climbField
-                            fact: autopilot.parameters["RTL_RETURN_ALT"]
+                            fact: Fact { name: "RTL_RETURN_ALT" }
                             showUnits: true
                         }
                     }
@@ -137,7 +137,8 @@ Rectangle {
 
                         QGCCheckBox {
                             id: homeLoiterCheckbox
-                            property Fact fact: autopilot.parameters["RTL_LAND_DELAY"]
+                            property Fact fact: Fact { name: "RTL_LAND_DELAY" }
+
                             checked: fact.value > 0
                             text: "Loiter at Home altitude for"
                             onClicked: {
@@ -145,7 +146,7 @@ Rectangle {
                             }
                         }
                         FactTextField {
-                            fact: autopilot.parameters["RTL_LAND_DELAY"];
+                            fact: Fact { name: "RTL_LAND_DELAY" }
                             showUnits: true
                             enabled: homeLoiterCheckbox.checked == true
                         }
@@ -251,7 +252,7 @@ Rectangle {
                         }
                         FactTextField {
                             id: descendField;
-                            fact: autopilot.parameters["RTL_DESCEND_ALT"];
+                            fact: Fact { name: "RTL_DESCEND_ALT" }
                             enabled: homeLoiterCheckbox.checked == true
                             showUnits: true
                         }
@@ -263,17 +264,19 @@ Rectangle {
         }
 
         QGCLabel {
+            property Fact fact: Fact { name: "NAV_RCL_OBC" }
             width: parent.width
             font.pointSize: 14
             text: "Warning: You have an advanced safety configuration set using the NAV_RCL_OBC parameter. The above settings may not apply.";
-            visible: autopilot.parameters["NAV_RCL_OBC"].value != 0
+            visible: fact.value != 0
             wrapMode: Text.Wrap
         }
         QGCLabel {
+            property Fact fact: Fact { name: "NAV_DLL_OBC" }
             width: parent.width
             font.pointSize: 14
             text: "Warning: You have an advanced safety configuration set using the NAV_DLL_OBC parameter. The above settings may not apply.";
-            visible: autopilot.parameters["NAV_DLL_OBC"].value != 0
+            visible: fact.value != 0
             wrapMode: Text.Wrap
         }
     }

src/AutoPilotPlugins/PX4/SafetyComponentSummary.qml

@@ -3,6 +3,7 @@ import QtQuick.Controls 1.2
 import QtQuick.Controls.Styles 1.2
 
 import QGroundControl.FactSystem 1.0
+import QGroundControl.FactControls 1.0
 import QGroundControl.Controls 1.0
 
 Column {
@@ -13,10 +14,10 @@ Column {
         width: parent.width
 
         QGCLabel { id: rtlMinAlt; text: "RTL min alt:" }
-        QGCLabel {
+        FactLabel {
+            fact: Fact { name: "RTL_RETURN_ALT" }
             horizontalAlignment: Text.AlignRight;
             width: parent.width - rtlMinAlt.contentWidth;
-            text: autopilot.parameters["RTL_RETURN_ALT"].valueString
         }
     }
 
@@ -24,10 +25,10 @@ Column {
         width: parent.width
 
         QGCLabel { id: rtlHomeAlt; text: "RTL home alt:" }
-        QGCLabel {
+        FactLabel {
+            fact: Fact { name: "RTL_DESCEND_ALT" }
             horizontalAlignment: Text.AlignRight;
             width: parent.width - rtlHomeAlt.contentWidth;
-            text: autopilot.parameters["RTL_DESCEND_ALT"].valueString
         }
     }
 
@@ -36,9 +37,10 @@ Column {
 
         QGCLabel { id: rtlLoiter; text: "RTL loiter delay:" }
         QGCLabel {
+            property Fact fact: Fact { name: "RTL_LAND_DELAY" }
             horizontalAlignment: Text.AlignRight;
             width: parent.width - rtlLoiter.contentWidth;
-            text: autopilot.parameters["RTL_LAND_DELAY"].value < 0 ? "Disabled" : autopilot.parameters["RTL_LAND_DELAY"].valueString
+            text: fact.value < 0 ? "Disabled" : fact.valueString
         }
     }
 
@@ -47,9 +49,10 @@ Column {
 
         QGCLabel { id: commLoss; text: "Telemetry loss RTL:" }
         QGCLabel {
+            property Fact fact: Fact { name: "COM_DL_LOSS_EN" }
             horizontalAlignment: Text.AlignRight;
             width: parent.width - commLoss.contentWidth;
-            text: autopilot.parameters["COM_DL_LOSS_EN"].value != 1 ? "Disabled" : autopilot.parameters["COM_DL_LOSS_T"].valueString
+            text: fact.value != 1 ? "Disabled" : fact.valueString
         }
     }
 
@@ -57,10 +60,10 @@ Column {
         width: parent.width
 
         QGCLabel { id: rcLoss; text: "RC loss RTL (seconds):" }
-        QGCLabel {
+        FactLabel {
+            fact: Fact { name: "COM_RC_LOSS_T" }
             horizontalAlignment: Text.AlignRight;
             width: parent.width - rcLoss.contentWidth;
-            text: autopilot.parameters["COM_RC_LOSS_T"].valueString
         }
     }
 }

src/AutoPilotPlugins/PX4/SensorsComponent.qml

@@ -75,33 +75,41 @@ Rectangle {
             QGCLabel { text: "Calibrate:"; anchors.baseline: firstButton.baseline }
 
             IndicatorButton {
+                property Fact fact: Fact { name: "CAL_MAG0_ID" }
+
                 id:             firstButton
                 width:          parent.buttonWidth
                 text:           "Compass"
-                indicatorGreen: autopilot.parameters["CAL_MAG0_ID"].value != 0
+                indicatorGreen: fact.value != 0
                 onClicked: controller.calibrateCompass()
             }
 
             IndicatorButton {
+                property Fact fact: Fact { name: "CAL_GYRO0_ID" }
+
                 width:          parent.buttonWidth
                 text:           "Gyroscope"
-                indicatorGreen: autopilot.parameters["CAL_GYRO0_ID"].value != 0
+                indicatorGreen: fact.value != 0
                 onClicked: controller.calibrateGyro()
             }
 
             IndicatorButton {
+                property Fact fact: Fact { name: "CAL_ACC0_ID" }
+
                 width:          parent.buttonWidth
                 text:           "Accelerometer"
-                indicatorGreen: autopilot.parameters["CAL_ACC0_ID"].value != 0
+                indicatorGreen: fact.value != 0
                 onClicked: controller.calibrateAccel()
             }
 
             IndicatorButton {
+                property Fact fact: Fact { name: "SENS_DPRES_OFF" }
+
                 width:          parent.buttonWidth
                 text:           "Airspeed"
                 visible:        controller.fixedWing
-                indicatorGreen: autopilot.parameters["SENS_DPRES_OFF"].value != 0
-                onClicked: controller.calibrateAirspeed()
+                indicatorGreen: fact.value != 0
+                onClicked:      controller.calibrateAirspeed()
             }
         }
 
@@ -232,11 +240,15 @@ Rectangle {
             }
 
             Column {
+                property Fact cal_mag0_rot: Fact { name: "CAL_MAG0_ROT" }
+                property Fact cal_mag1_rot: Fact { name: "CAL_MAG1_ROT" }
+                property Fact cal_mag2_rot: Fact { name: "CAL_MAG2_ROT" }
+
                 // Compass rotation parameter < 0 indicates either internal compass, or no compass. So in
                 // both those cases we do not show a rotation combo.
-                property bool showCompass0: autopilot.parameters["CAL_MAG0_ROT"].value >= 0
-                property bool showCompass1: autopilot.parameters["CAL_MAG1_ROT"].value >= 0
-                property bool showCompass2: autopilot.parameters["CAL_MAG2_ROT"].value >= 0
+                property bool showCompass0: cal_mag0_rot.value >= 0
+                property bool showCompass1: cal_mag1_rot.value >= 0
+                property bool showCompass2: cal_mag2_rot.value >= 0
 
                 x: parent.width - rotationColumnWidth
 
@@ -245,7 +257,7 @@ Rectangle {
                 FactComboBox {
                     width:  rotationColumnWidth;
                     model:  rotations
-                    fact:   autopilot.parameters["SENS_BOARD_ROT"]
+                    fact:   Fact { name: "SENS_BOARD_ROT" }
                 }
 
                 // Compass 0 rotation
@@ -260,7 +272,7 @@ Rectangle {
                     FactComboBox {
                         width:  rotationColumnWidth
                         model:  rotations
-                        fact:   autopilot.parameters["CAL_MAG0_ROT"]
+                        fact:   Fact { name: "CAL_MAG0_ROT" }
                     }
                 }
                 Loader { sourceComponent: parent.showCompass0 ? compass0ComponentLabel : null }
@@ -278,7 +290,7 @@ Rectangle {
                     FactComboBox {
                         width:  rotationColumnWidth
                         model:  rotations
-                        fact:   autopilot.parameters["CAL_MAG1_ROT"]
+                        fact:   Fact { name: "CAL_MAG1_ROT" }
                     }
                 }
                 Loader { sourceComponent: parent.showCompass1 ? compass1ComponentLabel : null }
@@ -296,7 +308,7 @@ Rectangle {
                     FactComboBox {
                         width:  rotationColumnWidth
                         model:  rotations
-                        fact:   autopilot.parameters["CAL_MAG2_ROT"]
+                        fact:   Fact { name: "CAL_MAG2_ROT" }
                     }
                 }
                 Loader { sourceComponent: parent.showCompass2 ? compass2ComponentLabel : null }

src/AutoPilotPlugins/PX4/SensorsComponentSummary.qml

@@ -13,36 +13,40 @@ Column {
     anchors.fill: parent
     anchors.margins: 8
 
-    Row {
-        width: parent.width
-
-        QGCLabel { id: compass; text: "Compass:" }
-        QGCLabel {
-            horizontalAlignment: Text.AlignRight;
-            width: parent.width - compass.contentWidth;
-            text: autopilot.parameters["CAL_MAG0_ID"].value  == 0 ? "Setup required" : "Ready"
+    Component {
+        id: component
+
+        Row {
+            width: parent.width
+
+            QGCLabel { id: label; text: labelText }
+            QGCLabel {
+                property Fact fact:     Fact { name: factName }
+                horizontalAlignment:    Text.AlignRight;
+                width:                  parent.width - label.contentWidth;
+                text:                   fact.value  == 0 ? "Setup required" : "Ready"
+            }
         }
     }
 
-    Row {
+    Loader {
+        property string labelText: "Compass:"
+        property string factName: "CAL_MAG0_ID"
         width: parent.width
-
-        QGCLabel { id: gyro; text: "Gyro:" }
-        QGCLabel {
-            horizontalAlignment: Text.AlignRight;
-            width: parent.width - gyro.contentWidth;
-            text: autopilot.parameters["CAL_GYRO0_ID"].value  == 0 ? "Setup required" : "Ready"
-        }
+        sourceComponent: component
     }
 
-    Row {
+    Loader {
+        property string labelText: "Gyro:"
+        property string factName: "CAL_GYRO0_ID"
         width: parent.width
+        sourceComponent: component
+    }
 
-        QGCLabel { id: accel; text: "Accelerometer:" }
-        QGCLabel {
-            horizontalAlignment: Text.AlignRight;
-            width: parent.width - accel.contentWidth;
-            text: autopilot.parameters["CAL_ACC0_ID"].value  == 0 ? "Setup required" : "Ready"
-        }
+    Loader {
+        property string labelText: "Accelerometer:"
+        property string factName: "CAL_ACC0_ID"
+        width: parent.width
+        sourceComponent: component
     }
 }

src/AutoPilotPlugins/PX4/SensorsComponentSummaryFixedWing.qml

@@ -18,9 +18,10 @@ Column {
 
         QGCLabel { id: compass; text: "Compass:" }
         QGCLabel {
-            horizontalAlignment: Text.AlignRight;
-            width: parent.width - compass.contentWidth;
-            text: autopilot.parameters["CAL_MAG0_ID"].value  == 0 ? "Setup required" : "Ready"
+            property Fact fact:     Fact { name: "CAL_MAG0_ID" }
+            horizontalAlignment:    Text.AlignRight;
+            width:                  parent.width - compass.contentWidth;
+            text:                   fact.value  == 0 ? "Setup required" : "Ready"
         }
     }
 
@@ -29,9 +30,10 @@ Column {
 
         QGCLabel { id: gyro; text: "Gyro:" }
         QGCLabel {
-            horizontalAlignment: Text.AlignRight;
-            width: parent.width - gyro.contentWidth;
-            text: autopilot.parameters["CAL_GYRO0_ID"].value  == 0 ? "Setup required" : "Ready"
+            property Fact fact:     Fact { name: "CAL_GYRO0_ID" }
+            horizontalAlignment:    Text.AlignRight;
+            width:                  parent.width - compass.contentWidth;
+            text:                   fact.value  == 0 ? "Setup required" : "Ready"
         }
     }
 
@@ -40,9 +42,10 @@ Column {
 
         QGCLabel { id: accel; text: "Accelerometer:" }
         QGCLabel {
-            horizontalAlignment: Text.AlignRight;
-            width: parent.width - accel.contentWidth;
-            text: autopilot.parameters["CAL_ACC0_ID"].value  == 0 ? "Setup required" : "Ready"
+            property Fact fact:     Fact { name: "CAL_ACC0_ID" }
+            horizontalAlignment:    Text.AlignRight;
+            width:                  parent.width - compass.contentWidth;
+            text:                   fact.value  == 0 ? "Setup required" : "Ready"
         }
     }
 
@@ -51,9 +54,10 @@ Column {
 
         QGCLabel { id: airspeed; text: "Airspeed:" }
         QGCLabel {
+            property Fact fact:     Fact { name: "SENS_DPRES_OFF" }
             horizontalAlignment: Text.AlignRight;
             width: parent.width - airspeed.contentWidth;
-            text: autopilot.parameters["SENS_DPRES_OFF"].value == 0.0 ? "Setup required" : "Ready"
+            text: fact.value == 0.0 ? "Setup required" : "Ready"
         }
     }
 }

src/FactSystem/FactBinder.cc

+/*=====================================================================
+ 
+ QGroundControl Open Source Ground Control Station
+ 
+ (c) 2009 - 2014 QGROUNDCONTROL PROJECT <http://www.qgroundcontrol.org>
+ 
+ This file is part of the QGROUNDCONTROL project
+ 
+ QGROUNDCONTROL is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+ 
+ QGROUNDCONTROL is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ GNU General Public License for more details.
+ 
+ You should have received a copy of the GNU General Public License
+ along with QGROUNDCONTROL. If not, see <http://www.gnu.org/licenses/>.
+ 
+ ======================================================================*/
+
+/// @file
+///     @author Don Gagne <don@thegagnes.com>
+
+#include "FactBinder.h"
+#include "UASManager.h"
+#include "AutoPilotPluginManager.h"
+
+FactBinder::FactBinder(void) :
+    _autopilotPlugin(NULL),
+    _fact(NULL)
+{
+    UASInterface* uas = UASManager::instance()->getActiveUAS();
+    Q_ASSERT(uas);
+    
+    _autopilotPlugin = AutoPilotPluginManager::instance()->getInstanceForAutoPilotPlugin(uas);
+    Q_ASSERT(_autopilotPlugin);
+    Q_ASSERT(_autopilotPlugin->pluginIsReady());
+}
+
+QString FactBinder::name(void) const
+{
+    if (_fact) {
+        return _fact->name();
+    } else {
+        return QString();
+    }
+}
+
+void FactBinder::setName(const QString& name)
+{
+    if (_fact) {
+        disconnect(_fact, &Fact::valueChanged, this, &FactBinder::valueChanged);
+        _fact = NULL;
+    }
+    
+    if (!name.isEmpty()) {
+        if (_autopilotPlugin->factExists(name)) {
+            _fact = _autopilotPlugin->getFact(name);
+            connect(_fact, &Fact::valueChanged, this, &FactBinder::valueChanged);
+        } else {
+            Q_ASSERT(false);
+        }
+    }
+    
+    emit valueChanged();
+    emit nameChanged();
+}
+
+QVariant FactBinder::value(void) const
+{
+    if (_fact) {
+        return _fact->value();
+    } else {
+        return QVariant(0);
+    }
+}
+
+void FactBinder::setValue(const QVariant& value)
+{
+    if (_fact) {
+        _fact->setValue(value);
+    } else {
+        Q_ASSERT(false);
+    }
+}
+
+QString FactBinder::valueString(void) const
+{
+    if (_fact) {
+        return _fact->valueString();
+    } else {
+        return QString();
+    }
+}
+
+QString FactBinder::units(void) const
+{
+    if (_fact) {
+        return _fact->units();
+    } else {
+        return QString();
+    }
+}

src/FactSystem/FactBinder.h

+/*=====================================================================
+ 
+ QGroundControl Open Source Ground Control Station
+ 
+ (c) 2009 - 2014 QGROUNDCONTROL PROJECT <http://www.qgroundcontrol.org>
+ 
+ This file is part of the QGROUNDCONTROL project
+ 
+ QGROUNDCONTROL is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+ 
+ QGROUNDCONTROL is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ GNU General Public License for more details.
+ 
+ You should have received a copy of the GNU General Public License
+ along with QGROUNDCONTROL. If not, see <http://www.gnu.org/licenses/>.
+ 
+ ======================================================================*/
+
+/// @file
+///     @author Don Gagne <don@thegagnes.com>
+
+#ifndef FACTBINDER_H
+#define FACTBINDER_H
+
+#include "Fact.h"
+#include "AutoPilotPlugin.h"
+
+#include <QObject>
+#include <QString>
+
+/// This object is used to instantiate a connection to a Fact from within Qml.
+class FactBinder : public QObject
+{
+    Q_OBJECT
+    
+    Q_PROPERTY(QString name READ name WRITE setName NOTIFY nameChanged)
+    Q_PROPERTY(QVariant value READ value WRITE setValue NOTIFY valueChanged USER true)
+    Q_PROPERTY(QVariant valueString READ valueString NOTIFY valueChanged)
+    Q_PROPERTY(QString units READ units CONSTANT)
+    
+public:
+    FactBinder(void);
+    
+    QString name(void) const;
+    void setName(const QString& name);
+    
+    QVariant value(void) const;
+    void setValue(const QVariant& value);
+    
+    QString valueString(void) const;
+    
+    /// Read accesor for units property
+    QString units(void) const;
+    
+signals:
+    void nameChanged(void);
+    void valueChanged(void);
+    
+private:
+    AutoPilotPlugin*    _autopilotPlugin;
+    Fact*               _fact;
+};
+
+#endif
\ No newline at end of file

src/FactSystem/FactControls/FactCheckBox.qml

@@ -7,7 +7,7 @@ import QGroundControl.Palette 1.0
 import QGroundControl.Controls 1.0
 
 QGCCheckBox {
-    property Fact fact: Fact { value: 0 }
+    property Fact fact: Fact { }
     property variant checkedValue: 1
     property variant uncheckedValue: 0
 

src/FactSystem/FactControls/FactComboBox.qml

@@ -7,7 +7,7 @@ import QGroundControl.Palette 1.0
 import QGroundControl.Controls 1.0
 
 QGCComboBox {
-    property Fact fact: Fact { value: 0 }
+    property Fact fact: Fact { }
     currentIndex: fact.value
     onActivated: fact.value = index
 }

src/FactSystem/FactControls/FactLabel.qml

@@ -7,6 +7,6 @@ import QGroundControl.Palette 1.0
 import QGroundControl.Controls 1.0
 
 QGCLabel {
-    property Fact fact: Fact { value: "FactLabel" }
+    property Fact fact: Fact { }
     text: fact.valueString
 }

src/FactSystem/FactControls/FactTextField.qml

@@ -7,7 +7,7 @@ import QGroundControl.Palette 1.0
 import QGroundControl.Controls 1.0
 
 QGCTextField {
-    property Fact fact: Fact { value: 0 }
+    property Fact fact: Fact { }
     text: fact.valueString
     unitsLabel: fact.units
     onEditingFinished: fact.value = text

src/FactSystem/FactLoader.h

@@ -38,14 +38,6 @@
 Q_DECLARE_LOGGING_CATEGORY(FactLoaderLog)
 
 /// Connects to Parameter Manager to load/update Facts
-///
-/// These Facts are available for binding within QML code. For example:
-/// @code{.unparsed}
-///     TextInput {
-///         text: autopilot.parameters["RC_MAP_THROTTLE"].value
-///     }
-/// @endcode
-
 class FactLoader : public QObject
 {
     Q_OBJECT

src/FactSystem/FactSystem.cc

@@ -28,6 +28,7 @@
 #include "UASManager.h"
 #include "QGCApplication.h"
 #include "VehicleComponent.h"
+#include "FactBinder.h"
 
 #include <QtQml>
 
@@ -38,8 +39,7 @@ const char* FactSystem::_factSystemQmlUri = "QGroundControl.FactSystem";
 FactSystem::FactSystem(QObject* parent) :
     QGCSingleton(parent)
 {
-    qmlRegisterType<Fact>(_factSystemQmlUri, 1, 0, "Fact");
-    qmlRegisterType<FactValidator>(_factSystemQmlUri, 1, 0, "FactValidator");
+    qmlRegisterType<FactBinder>(_factSystemQmlUri, 1, 0, "Fact");
     
     // FIXME: Where should these go?
     qmlRegisterUncreatableType<VehicleComponent>(_factSystemQmlUri, 1, 0, "VehicleComponent", "Can only reference VehicleComponent");

src/FactSystem/FactSystemTest.qml

@@ -5,11 +5,12 @@ import QGroundControl.FactSystem 1.0
 Item {
     TextInput {
         objectName: "testControl"
-        text: autopilot.parameters["RC_MAP_THROTTLE"].value
+        Fact { id: fact; name: "RC_MAP_THROTTLE" }
+        text: fact.value
         font.family: "Helvetica"
         font.pointSize: 24
         color: "red"
         focus: true
-        onAccepted: { autopilot.parameters["RC_MAP_THROTTLE"].value = text; }
+        onAccepted: { fact.value = text; }
     }
 }
\ No newline at end of file

src/QmlControls/QmlTest.qml

@@ -4,7 +4,6 @@ import QtQuick.Controls.Styles 1.2
 
 import QGroundControl.Palette 1.0
 import QGroundControl.Controls 1.0
-import QGroundControl.FactControls 1.0
 
 Rectangle {
 
@@ -449,55 +448,6 @@ Rectangle {
                     enabled: false
                 }
 
-                // FactLabel
-                Loader {
-                    sourceComponent: ctlRowHeader
-                    property var text: "FactLabel"
-                }
-                FactLabel {
-                    width: 100
-                    height: 20
-                }
-                FactLabel {
-                    width: 100
-                    height: 20
-                    enabled: false
-                }
-
-                // FactCheckBox
-                Loader {
-                    sourceComponent: ctlRowHeader
-                    property var text: "FactCheckBox"
-                }
-                FactCheckBox {
-                    width: 100
-                    height: 20
-                    text: "Fact CheckBox"
-                }
-                FactCheckBox {
-                    width: 100
-                    height: 20
-                    text: "Fact CheckBox"
-                    enabled: false
-                }
-
-                // FactTextField
-                Loader {
-                    sourceComponent: ctlRowHeader
-                    property var text: "FactTextField"
-                }
-                FactTextField {
-                    width: 100
-                    height: 20
-                    text: "FactTextField"
-                }
-                FactTextField {
-                    width: 100
-                    height: 20
-                    text: "FactTextField"
-                    enabled: false
-                }
-
                 // QGCComboBox
                 Loader {
                     sourceComponent: ctlRowHeader