Cleanup: unify idiosyncratic singletons

The way we handle singletons in QML, QML insists on allocating the
objects. This leads to a very idiosyncratic way of handling
singletons: The global instance pointer is set in the constructor.

Unify all these by implementing a "SillySingleton" template. All
of the weird singleton-classes can derive from this template and
don't have to bother with reimplementing the instance() function
with all the safety-checks, etc.

This serves firstly as documentation but also improves debugging
as we will now see wanted and unwanted creation and destruction
of these weird singletons.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

2 files changed, 2 insertions, 13 deletions

diff --git a/desktop-widgets/mainwindow.cpp b/desktop-widgets/mainwindow.cpp
index bed142ecc..ef55b3d06 100644
--- a/desktop-widgets/mainwindow.cpp
+++ b/desktop-widgets/mainwindow.cpp
@@ -109,8 +109,6 @@ extern "C" int updateProgress(const char *text)
 	return progressDialogCanceled;
 }
 
-MainWindow *MainWindow::m_Instance = nullptr;
-
 extern "C" void showErrorFromC(char *buf)
 {
 	QString error(buf);
@@ -128,8 +126,6 @@ MainWindow::MainWindow() : QMainWindow(),
 	survey(nullptr),
 	findMovedImagesDialog(nullptr)
 {
-	Q_ASSERT_X(m_Instance == NULL, "MainWindow", "MainWindow recreated!");
-	m_Instance = this;
 	ui.setupUi(this);
 	read_hashes();
 	Command::init();
@@ -357,7 +353,6 @@ MainWindow::MainWindow() : QMainWindow(),
 MainWindow::~MainWindow()
 {
 	write_hashes();
-	m_Instance = nullptr;
 }
 
 void MainWindow::setupSocialNetworkMenu()
@@ -398,11 +393,6 @@ void MainWindow::setDefaultState()
 		ui.bottomLeft->currentWidget()->setEnabled(false);
 }
 
-MainWindow *MainWindow::instance()
-{
-	return m_Instance;
-}
-
 // This gets called after one or more dives were added, edited or downloaded for a dive computer
 void MainWindow::refreshDisplay(bool doRecreateDiveList)
 {
diff --git a/desktop-widgets/mainwindow.h b/desktop-widgets/mainwindow.h
index 62cc1b6f1..4b91b0dc3 100644
--- a/desktop-widgets/mainwindow.h
+++ b/desktop-widgets/mainwindow.h
@@ -21,6 +21,7 @@
 #include "desktop-widgets/filterwidget2.h"
 #include "core/applicationstate.h"
 #include "core/gpslocation.h"
+#include "core/singleton.h"
 
 #define NUM_RECENT_FILES 4
 
@@ -42,7 +43,7 @@ class LocationInformationWidget;
 typedef std::pair<QByteArray, QVariant> WidgetProperty;
 typedef QVector<WidgetProperty> PropertyList;
 
-class MainWindow : public QMainWindow {
+class MainWindow : public QMainWindow, public SillySingleton<MainWindow> {
 	Q_OBJECT
 public:
 	enum {
@@ -61,7 +62,6 @@ public:
 
 	MainWindow();
 	~MainWindow();
-	static MainWindow *instance();
 	void loadRecentFiles();
 	void updateRecentFiles();
 	void updateRecentFilesMenu();
@@ -193,7 +193,6 @@ private:
 	QString filter_open();
 	QString filter_import();
 	QString filter_import_dive_sites();
-	static MainWindow *m_Instance;
 	QString displayedFilename(QString fullFilename);
 	bool askSaveChanges();
 	bool okToClose(QString message);