Use Qt signal for macOS Dock icon click event

This moves the Dock icon click reaction code to the common place and
allows some cleanup in obj_c code.

According to the Apple's docs `class_replaceMethod` behaves as
`class_addMethod`, if the method identified by name does not yet exist;
or as `method_setImplementation`, if it does exist.

src/qt/bitcoingui.cpp

@@ -595,7 +595,7 @@ void BitcoinGUI::createTrayIcon(const NetworkStyle *networkStyle)
 void BitcoinGUI::createTrayIconMenu()
 {
 #ifndef Q_OS_MAC
-    // return if trayIcon is unset (only on non-Mac OSes)
+    // return if trayIcon is unset (only on non-macOSes)
     if (!trayIcon)
         return;
 
@@ -604,15 +604,15 @@ void BitcoinGUI::createTrayIconMenu()
 
     connect(trayIcon, &QSystemTrayIcon::activated, this, &BitcoinGUI::trayIconActivated);
 #else
-    // Note: On Mac, the dock icon is used to provide the tray's functionality.
+    // Note: On macOS, the Dock icon is used to provide the tray's functionality.
     MacDockIconHandler *dockIconHandler = MacDockIconHandler::instance();
-    dockIconHandler->setMainWindow(static_cast<QMainWindow*>(this));
+    connect(dockIconHandler, &MacDockIconHandler::dockIconClicked, this, &BitcoinGUI::macosDockIconActivated);
     trayIconMenu = dockIconHandler->dockMenu();
 #endif
 
-    // Configuration of the tray icon (or dock icon) icon menu
+    // Configuration of the tray icon (or Dock icon) menu
 #ifndef Q_OS_MAC
-    // Note: On Mac, the dock icon's menu already has show / hide action.
+    // Note: On macOS, the Dock icon's menu already has Show / Hide action.
     trayIconMenu->addAction(toggleHideAction);
     trayIconMenu->addSeparator();
 #endif
@@ -626,7 +626,7 @@ void BitcoinGUI::createTrayIconMenu()
         trayIconMenu->addAction(openRPCConsoleAction);
     }
     trayIconMenu->addAction(optionsAction);
-#ifndef Q_OS_MAC // This is built-in on Mac
+#ifndef Q_OS_MAC // This is built-in on macOS
     trayIconMenu->addSeparator();
     trayIconMenu->addAction(quitAction);
 #endif
@@ -641,6 +641,12 @@ void BitcoinGUI::trayIconActivated(QSystemTrayIcon::ActivationReason reason)
         toggleHidden();
     }
 }
+#else
+void BitcoinGUI::macosDockIconActivated()
+{
+    show();
+    activateWindow();
+}
 #endif
 
 void BitcoinGUI::optionsClicked()

src/qt/bitcoingui.h

@@ -260,6 +260,9 @@ public Q_SLOTS:
 #ifndef Q_OS_MAC
     /** Handle tray icon clicked */
     void trayIconActivated(QSystemTrayIcon::ActivationReason reason);
+#else
+    /** Handle macOS Dock icon clicked */
+    void macosDockIconActivated();
 #endif
 
     /** Show window if hidden, unminimize when minimized, rise when obscured or show if hidden and fToggleHidden is true */

src/qt/macdockiconhandler.h

@@ -1,11 +1,10 @@
-// Copyright (c) 2011-2015 The Bitcoin Core developers
+// Copyright (c) 2011-2018 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #ifndef BITCOIN_QT_MACDOCKICONHANDLER_H
 #define BITCOIN_QT_MACDOCKICONHANDLER_H
 
-#include <QMainWindow>
 #include <QObject>
 
 QT_BEGIN_NAMESPACE
@@ -13,7 +12,7 @@ class QMenu;
 class QWidget;
 QT_END_NAMESPACE
 
-/** Macintosh-specific dock icon handler.
+/** macOS-specific Dock icon handler.
  */
 class MacDockIconHandler : public QObject
 {
@@ -23,10 +22,8 @@ public:
     ~MacDockIconHandler();
 
     QMenu *dockMenu();
-    void setMainWindow(QMainWindow *window);
     static MacDockIconHandler *instance();
     static void cleanup();
-    void handleDockIconClickEvent();
 
 Q_SIGNALS:
     void dockIconClicked();
@@ -36,7 +33,6 @@ private:
 
     QWidget *m_dummyWidget;
     QMenu *m_dockMenu;
-    QMainWindow *mainWindow;
 };
 
 #endif // BITCOIN_QT_MACDOCKICONHANDLER_H

src/qt/macdockiconhandler.mm

@@ -1,4 +1,4 @@
-// Copyright (c) 2011-2013 The Bitcoin Core developers
+// Copyright (c) 2011-2018 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -18,25 +18,18 @@ bool dockClickHandler(id self,SEL _cmd,...) {
     Q_UNUSED(self)
     Q_UNUSED(_cmd)
 
-    s_instance->handleDockIconClickEvent();
+    Q_EMIT s_instance->dockIconClicked();
 
-    // Return NO (false) to suppress the default OS X actions
+    // Return NO (false) to suppress the default macOS actions
     return false;
 }
 
 void setupDockClickHandler() {
-    Class cls = objc_getClass("NSApplication");
-    id appInst = objc_msgSend((id)cls, sel_registerName("sharedApplication"));
-
-    if (appInst != nullptr) {
-        id delegate = objc_msgSend(appInst, sel_registerName("delegate"));
-        Class delClass = (Class)objc_msgSend(delegate,  sel_registerName("class"));
-        SEL shouldHandle = sel_registerName("applicationShouldHandleReopen:hasVisibleWindows:");
-        if (class_getInstanceMethod(delClass, shouldHandle))
-            class_replaceMethod(delClass, shouldHandle, (IMP)dockClickHandler, "B@:");
-        else
-            class_addMethod(delClass, shouldHandle, (IMP)dockClickHandler,"B@:");
-    }
+    id app = objc_msgSend((id)objc_getClass("NSApplication"), sel_registerName("sharedApplication"));
+    id delegate = objc_msgSend(app, sel_registerName("delegate"));
+    Class delClass = (Class)objc_msgSend(delegate, sel_registerName("class"));
+    SEL shouldHandle = sel_registerName("applicationShouldHandleReopen:hasVisibleWindows:");
+    class_replaceMethod(delClass, shouldHandle, (IMP)dockClickHandler, "B@:");
 }
 
 
@@ -47,21 +40,15 @@ MacDockIconHandler::MacDockIconHandler() : QObject()
     setupDockClickHandler();
     this->m_dummyWidget = new QWidget();
     this->m_dockMenu = new QMenu(this->m_dummyWidget);
-    this->setMainWindow(nullptr);
 #if QT_VERSION >= 0x050200
     this->m_dockMenu->setAsDockMenu();
 #endif
     [pool release];
 }
 
-void MacDockIconHandler::setMainWindow(QMainWindow *window) {
-    this->mainWindow = window;
-}
-
 MacDockIconHandler::~MacDockIconHandler()
 {
     delete this->m_dummyWidget;
-    this->setMainWindow(nullptr);
 }
 
 QMenu *MacDockIconHandler::dockMenu()
@@ -80,14 +67,3 @@ void MacDockIconHandler::cleanup()
 {
     delete s_instance;
 }
-
-void MacDockIconHandler::handleDockIconClickEvent()
-{
-    if (this->mainWindow)
-    {
-        this->mainWindow->activateWindow();
-        this->mainWindow->show();
-    }
-
-    Q_EMIT this->dockIconClicked();
-}