Use single instance application to handle multiple windows.

.gitmodules

@@ -2,3 +2,6 @@
 	path = qmltermwidget
 	url = https://github.com/Swordfish90/qmltermwidget
 	branch = unstable
+[submodule "singleapplication"]
+	path = singleapplication
+	url = https://github.com/itay-grudev/SingleApplication.git

app/app.pro

@@ -1,13 +1,16 @@
 QT += qml quick widgets sql quickcontrols2
+DEFINES += QAPPLICATION_CLASS=QApplication
 TARGET = cool-retro-term 
 
+include(../singleapplication/singleapplication.pri)
+
 DESTDIR = $$OUT_PWD/../
 
 HEADERS += \
     fileio.h \
     monospacefontmanager.h
 
-SOURCES = main.cpp \
+SOURCES += main.cpp \
     fileio.cpp \
     monospacefontmanager.cpp
 

app/main.cpp

@@ -8,6 +8,8 @@
 #include <QIcon>
 #include <QQuickStyle>
 
+#include <singleapplication.h>
+
 #include <QDebug>
 #include <stdlib.h>
 
@@ -78,9 +80,14 @@ int main(int argc, char *argv[])
         return 0;
     }
 
-    QApplication app(argc, argv);
+    SingleApplication app(argc, argv, true);
     app.setAttribute(Qt::AA_MacDontSwapCtrlAndMeta, true);
 
+    if (app.isSecondary()) {
+        app.sendMessage("new-window");
+        return 0;
+    }
+
     QQmlApplicationEngine engine;
     FileIO fileIO;
     MonospaceFontManager monospaceFontManager;
@@ -135,5 +142,20 @@ int main(int argc, char *argv[])
     // Quit the application when the engine closes.
     QObject::connect((QObject*) &engine, SIGNAL(quit()), (QObject*) &app, SLOT(quit()));
 
+    auto requestNewWindow = [&engine]() {
+        if (engine.rootObjects().isEmpty())
+            return;
+
+        QObject *rootObject = engine.rootObjects().constFirst();
+        QMetaObject::invokeMethod(rootObject, "createWindow", Qt::QueuedConnection);
+    };
+
+    QObject::connect(&app, &SingleApplication::receivedMessage, &app,
+                     [&requestNewWindow](quint32 instanceId, QByteArray message) {
+        Q_UNUSED(instanceId);
+        if (message.isEmpty() || message == QByteArray("new-window"))
+            requestNewWindow();
+    });
+
     return app.exec();
 }

app/qml/SettingsWindow.qml

@@ -30,7 +30,7 @@ ApplicationWindow {
     id: settings_window
     title: qsTr("Settings")
     width: 640
-    height: 480
+    height: 520
 
     Item {
         anchors { fill: parent; }

app/qml/TerminalTabs.qml

@@ -44,10 +44,6 @@ Item {
         }
     }
 
-    function closeCurrentTab() {
-        closeTab(tabBar.currentIndex)
-    }
-
     ListModel {
         id: tabsModel
     }

app/qml/TerminalWindow.qml

@@ -148,12 +148,6 @@ ApplicationWindow {
         text: qsTr("New Tab")
         onTriggered: terminalTabs.addTab()
     }
-    Action {
-        id: closeTabAction
-        text: qsTr("Close Tab")
-        enabled: terminalTabs.count > 1
-        onTriggered: terminalTabs.closeCurrentTab()
-    }
     TerminalTabs {
         id: terminalTabs
         width: parent.width

app/qml/menus/FullContextMenu.qml

@@ -32,19 +32,15 @@ Menu {
         action: showsettingsAction
     }
 
-    MenuSeparator {}
     Menu {
-        title: qsTr("Tabs")
+        title: qsTr("File")
+        MenuItem {
+            action: newWindowAction
+        }
         MenuItem {
             action: newTabAction
         }
-        MenuItem {
+        MenuSeparator {}
-            action: closeTabAction
-        }
-    }
-
-    Menu {
-        title: qsTr("File")
         MenuItem {
             action: quitAction
         }

app/qml/menus/OSXMenu.qml

@@ -31,6 +31,12 @@ MenuBar {
             shortcut: newWindowAction.shortcut
             onTriggered: newWindowAction.trigger()
         }
+        MenuItem {
+            text: newTabAction.text
+            shortcut: newTabAction.shortcut
+            onTriggered: newTabAction.trigger()
+        }
+        MenuSeparator {}
         MenuItem {
             text: quitAction.text
             onTriggered: quitAction.trigger()

app/qml/menus/ShortContextMenu.qml

@@ -28,14 +28,4 @@ Menu {
     MenuItem {
         action: pasteAction
     }
-    MenuSeparator {}
-    Menu {
-        title: qsTr("Tabs")
-        MenuItem {
-            action: newTabAction
-        }
-        MenuItem {
-            action: closeTabAction
-        }
-    }
 }

app/qml/menus/WindowMenu.qml

@@ -29,6 +29,10 @@ MenuBar {
         MenuItem {
             action: newWindowAction
         }
+        MenuItem {
+            action: newTabAction
+        }
+        MenuSeparator {}
         MenuItem {
             action: quitAction
         }

cool-retro-term.desktop

@@ -9,3 +9,8 @@ StartupNotify=true
 Terminal=false
 Type=Application
 Keywords=shell;prompt;command;commandline;
+Actions=NewWindow;
+
+[Desktop Action NewWindow]
+Name=New Window
+Exec=cool-retro-term