Wire monitored property to OPC UA monitored items

The monitored bool now calls enableMonitoring/disableMonitoring on
the Value attribute. Adds publishingInterval property (default 100ms).
Value is no longer read at init — delivered by the monitored item.
Empty 4th demo page to verify monitoring stops when navigating away.

3 files changed, 104 insertions, 5 deletions

diff --git a/demo/NodePage.qml b/demo/NodePage.qml
index 442a6fd..a8e07d5 100644
--- a/demo/NodePage.qml
+++ b/demo/NodePage.qml
@@ -57,6 +57,12 @@ Page {
                 "ns=1;s=double_rw_array",
                 "ns=1;s=string_rw_array"
             ]
+        },
+        {
+            title: "Empty (Monitoring Test)",
+            description: "No nodes on this page. All previous pages are inactive,"
+                + " so the server log should show zero active monitored items.",
+            nodes: []
         }
     ]
 
@@ -78,7 +84,7 @@ Page {
                 font.pointSize: 14
             }
             Label {
-                text: "(" + nodePage.pageNumber + "/3)"
+                text: "(" + nodePage.pageNumber + "/" + nodePage.pages.length + ")"
                 color: "gray"
             }
             Item { Layout.fillWidth: true }
@@ -88,6 +94,16 @@ Page {
             }
         }
 
+        Label {
+            id: pageDescription
+            visible: currentPage.description !== undefined
+            text: currentPage.description || ""
+            wrapMode: Text.WordWrap
+            color: "gray"
+            font.italic: true
+            Layout.fillWidth: true
+        }
+
         // Column headers
         RowLayout {
             Layout.fillWidth: true
@@ -216,7 +232,7 @@ Page {
             Item { Layout.fillWidth: true }
             Button {
                 text: "Next →"
-                visible: nodePage.pageNumber < 3
+                visible: nodePage.pageNumber < nodePage.pages.length
                 onClicked: nodePage.stackRef.push("NodePage.qml", {
                     stackRef: nodePage.stackRef,
                     pageNumber: nodePage.pageNumber + 1,
diff --git a/src/OpcUaMonitoredNode.cpp b/src/OpcUaMonitoredNode.cpp
index 518ddd5..1a2da86 100644
--- a/src/OpcUaMonitoredNode.cpp
+++ b/src/OpcUaMonitoredNode.cpp
@@ -7,6 +7,7 @@
 
 #include <QMetaEnum>
 #include <QOpcUaLocalizedText>
+#include <QOpcUaMonitoringParameters>
 #include <QStringList>
 
 OpcUaMonitoredNode::OpcUaMonitoredNode (QObject *parent) : QObject (parent) {}
@@ -51,6 +52,29 @@ OpcUaMonitoredNode::setMonitored (bool monitored)
     return;
   m_monitored = monitored;
   emit monitoredChanged ();
+
+  if (!m_componentComplete || !m_node)
+    return;
+
+  if (m_monitored)
+    startMonitoring ();
+  else
+    stopMonitoring ();
+}
+
+double
+OpcUaMonitoredNode::publishingInterval () const
+{
+  return m_publishingInterval;
+}
+
+void
+OpcUaMonitoredNode::setPublishingInterval (double interval)
+{
+  if (qFuzzyCompare (m_publishingInterval, interval))
+    return;
+  m_publishingInterval = interval;
+  emit publishingIntervalChanged ();
 }
 
 QVariant
@@ -122,11 +146,18 @@ OpcUaMonitoredNode::setupNode ()
            &OpcUaMonitoredNode::handleValueUpdated);
   connect (m_node, &QOpcUaNode::attributeWritten, this,
            &OpcUaMonitoredNode::handleAttributeWritten);
+  connect (m_node, &QOpcUaNode::enableMonitoringFinished, this,
+           &OpcUaMonitoredNode::handleEnableMonitoringFinished);
+  connect (m_node, &QOpcUaNode::disableMonitoringFinished, this,
+           &OpcUaMonitoredNode::handleDisableMonitoringFinished);
 
   m_node->readAttributes (
-      QOpcUa::NodeAttribute::Value | QOpcUa::NodeAttribute::DisplayName
-      | QOpcUa::NodeAttribute::Description | QOpcUa::NodeAttribute::NodeClass
-      | QOpcUa::NodeAttribute::DataType | QOpcUa::NodeAttribute::AccessLevel);
+      QOpcUa::NodeAttribute::DisplayName | QOpcUa::NodeAttribute::Description
+      | QOpcUa::NodeAttribute::NodeClass | QOpcUa::NodeAttribute::DataType
+      | QOpcUa::NodeAttribute::AccessLevel);
+
+  if (m_monitored)
+    startMonitoring ();
 }
 
 void
@@ -153,6 +184,23 @@ OpcUaMonitoredNode::teardownNode ()
     }
 }
 
+void
+OpcUaMonitoredNode::startMonitoring ()
+{
+  if (!m_node || !m_monitored)
+    return;
+  QOpcUaMonitoringParameters params (m_publishingInterval);
+  m_node->enableMonitoring (QOpcUa::NodeAttribute::Value, params);
+}
+
+void
+OpcUaMonitoredNode::stopMonitoring ()
+{
+  if (!m_node)
+    return;
+  m_node->disableMonitoring (QOpcUa::NodeAttribute::Value);
+}
+
 /* ======================================
  *  Signal handlers
  * ====================================== */
@@ -262,6 +310,28 @@ OpcUaMonitoredNode::handleAttributeWritten (QOpcUa::NodeAttribute attr,
                               : QOpcUa::statusToString (statusCode));
 }
 
+void
+OpcUaMonitoredNode::handleEnableMonitoringFinished (
+    QOpcUa::NodeAttribute attr, QOpcUa::UaStatusCode statusCode)
+{
+  if (attr != QOpcUa::NodeAttribute::Value)
+    return;
+  if (statusCode != QOpcUa::Good)
+    qWarning () << "OpcUaMonitoredNode: enableMonitoring failed for"
+                << m_nodeId << ":" << QOpcUa::statusToString (statusCode);
+}
+
+void
+OpcUaMonitoredNode::handleDisableMonitoringFinished (
+    QOpcUa::NodeAttribute attr, QOpcUa::UaStatusCode statusCode)
+{
+  if (attr != QOpcUa::NodeAttribute::Value)
+    return;
+  if (statusCode != QOpcUa::Good)
+    qWarning () << "OpcUaMonitoredNode: disableMonitoring failed for"
+                << m_nodeId << ":" << QOpcUa::statusToString (statusCode);
+}
+
 /* ======================================
  *  Write support
  * ====================================== */
diff --git a/src/OpcUaMonitoredNode.h b/src/OpcUaMonitoredNode.h
index 5895bea..3e86cb4 100644
--- a/src/OpcUaMonitoredNode.h
+++ b/src/OpcUaMonitoredNode.h
@@ -56,6 +56,8 @@ class OpcUaMonitoredNode : public QObject, public QQmlParserStatus
   Q_PROPERTY (QString nodeId READ nodeId WRITE setNodeId NOTIFY nodeIdChanged)
   Q_PROPERTY (
       bool monitored READ monitored WRITE setMonitored NOTIFY monitoredChanged)
+  Q_PROPERTY (double publishingInterval READ publishingInterval WRITE
+                  setPublishingInterval NOTIFY publishingIntervalChanged)
   Q_PROPERTY (QVariant value READ value NOTIFY valueChanged)
   Q_PROPERTY (bool writable READ writable NOTIFY writableChanged)
   Q_PROPERTY (OpcUaNodeInfo info READ info NOTIFY infoChanged)
@@ -69,6 +71,9 @@ public:
   bool monitored () const;
   void setMonitored (bool monitored);
 
+  double publishingInterval () const;
+  void setPublishingInterval (double interval);
+
   QVariant value () const;
   bool writable () const;
   OpcUaNodeInfo info () const;
@@ -89,6 +94,7 @@ public:
 signals:
   void nodeIdChanged ();
   void monitoredChanged ();
+  void publishingIntervalChanged ();
   void valueChanged ();
   void writableChanged ();
   void infoChanged ();
@@ -101,14 +107,21 @@ private slots:
   void handleClientConnectedChanged ();
   void handleAttributeWritten (QOpcUa::NodeAttribute attr,
                                QOpcUa::UaStatusCode statusCode);
+  void handleEnableMonitoringFinished (QOpcUa::NodeAttribute attr,
+                                       QOpcUa::UaStatusCode statusCode);
+  void handleDisableMonitoringFinished (QOpcUa::NodeAttribute attr,
+                                        QOpcUa::UaStatusCode statusCode);
 
 private:
   void setupNode ();
   void teardownNode ();
+  void startMonitoring ();
+  void stopMonitoring ();
   QVariant coerceValue (const QVariant &input) const;
 
   QString m_nodeId;
   bool m_monitored = true;
+  double m_publishingInterval = 100.0;
   bool m_componentComplete = false;
 
   QOpcUaNode *m_node = nullptr;