[FEATURE] Add system tray notifcation for finished tasks.

Should work on all platforms and only shows when application is hidden.

src/app/qgisapp.cpp

@@ -58,6 +58,7 @@
 #endif
 #include <QStatusBar>
 #include <QStringList>
+#include <QSystemTrayIcon>
 #include <QTcpSocket>
 #include <QTextStream>
 #include <QtGlobal>
@@ -1126,6 +1127,12 @@ QgisApp::QgisApp( QSplashScreen *splash, bool restorePlugins, bool skipVersionCh
   }
 
 
+  mTray = new QSystemTrayIcon();
+  mTray->setIcon( QIcon( QgsApplication::appIconPath() ) );
+  mTray->show();
+
+  connect( QgsApplication::taskManager(), &QgsTaskManager::statusChanged, this, &QgisApp::onTaskCompleteShowNotify );
+
 #ifdef Q_OS_WIN
   QWinTaskbarButton *taskButton = new QWinTaskbarButton( this );
   taskButton->setWindow( windowHandle() );
@@ -1353,6 +1360,8 @@ QgisApp::~QgisApp()
   delete QgsProject::instance();
 
   delete mPythonUtils;
+
+  delete mTray;
 }
 
 void QgisApp::dragEnterEvent( QDragEnterEvent *event )
@@ -11398,6 +11407,19 @@ void QgisApp::keyPressEvent( QKeyEvent *e )
   }
 }
 
+void QgisApp::onTaskCompleteShowNotify( long taskId, int status )
+{
+  if ( status == QgsTask::Complete && !this->isActiveWindow() )
+  {
+    QgsTask *task = QgsApplication::taskManager()->task( taskId );
+    if ( task )
+    {
+      QString description = task->description();
+      mTray->showMessage( "Task Complete", description );
+    }
+  }
+}
+
 void QgisApp::onTransactionGroupsChanged()
 {
   Q_FOREACH ( QgsTransactionGroup *tg, QgsProject::instance()->transactionGroups().values() )

src/app/qgisapp.h

@@ -36,6 +36,7 @@ class QStringList;
 class QToolButton;
 class QTcpSocket;
 class QValidator;
+class QSystemTrayIcon;
 
 class QgisAppInterface;
 class QgisAppStyleSheet;
@@ -747,6 +748,8 @@ class APP_EXPORT QgisApp : public QMainWindow, private Ui::MainWindow
 #endif
 
   private slots:
+    void onTaskCompleteShowNotify( long taskId, int status );
+
     void onTransactionGroupsChanged();
 
     void onSnappingConfigChanged();
@@ -1858,6 +1861,8 @@ class APP_EXPORT QgisApp : public QMainWindow, private Ui::MainWindow
     bool gestureEvent( QGestureEvent *event );
     void tapAndHoldTriggered( QTapAndHoldGesture *gesture );
 
+    QSystemTrayIcon *mTray = nullptr;
+
     friend class TestQgisAppPython;
 };
 
@@ -1868,4 +1873,3 @@ class APP_EXPORT QgisApp : public QMainWindow, private Ui::MainWindow
 #endif
 
 #endif
-