Use queued connection to thread-safe MainWindow error handling

Up to now, errors produced by threads were not directly shown in
the MainWindow. Code running in the GUI thread had to manually
show the errors.

This can be simplified by using Qt's queued connection as message
passing facility.

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

desktop-widgets/downloadfromdivecomputer.cpp

@@ -222,9 +222,6 @@ void DownloadFromDCWidget::updateState(states state)
 	else if (state == ERROR) {
 		timer->stop();
 
-		// Show messages that worker thread produced.
-		MainWindow::instance()->showErrors();
-
 		QMessageBox::critical(this, TITLE_OR_TEXT(tr("Error"), thread.error), QMessageBox::Ok);
 		markChildrenAsEnabled();
 		progress_bar_text = "";

desktop-widgets/mainwindow.cpp

@@ -91,21 +91,9 @@ MainWindow *MainWindow::m_Instance = NULL;
 
 extern "C" void showErrorFromC()
 {
-	// Show errors only if we are running in the GUI thread.
-	// If we're not in the GUI thread, let errors accumulate.
-	if (QThread::currentThread() != QCoreApplication::instance()->thread())
-		return;
-
 	MainWindow *mainwindow = MainWindow::instance();
 	if (mainwindow)
-		mainwindow->showErrors();
+		emit mainwindow->showError(get_error_string());
-}
-
-void MainWindow::showErrors()
-{
-	const char *error = get_error_string();
-	if (!empty_string(error))
-		getNotificationWidget()->showNotification(error, KMessageWidget::Error);
 }
 
 MainWindow::MainWindow() : QMainWindow(),
@@ -219,6 +207,7 @@ MainWindow::MainWindow() : QMainWindow(),
 	connect(plannerDetails->printPlan(), SIGNAL(pressed()), divePlannerWidget(), SLOT(printDecoPlan()));
 	connect(this, SIGNAL(startDiveSiteEdit()), this, SLOT(on_actionDiveSiteEdit_triggered()));
 	connect(information(), SIGNAL(diveSiteChanged(struct dive_site *)), mapWidget, SLOT(centerOnDiveSite(struct dive_site *)));
+	connect(this, &MainWindow::showError, ui.mainErrorMessage, &NotificationWidget::showError, Qt::AutoConnection);
 
 	wtu = new WindowTitleUpdate();
 	connect(WindowTitleUpdate::instance(), SIGNAL(updateTitle()), this, SLOT(setAutomaticTitle()));

desktop-widgets/mainwindow.h

@@ -88,10 +88,6 @@ public:
 	void enableDisableCloudActions();
 	void setCheckedActionFilterTags(bool checked);
 
-	// Shows errors that have accumulated.
-	// Must be called from GUI thread.
-	void showErrors();
-
 private
 slots:
 	/* file menu action */
@@ -159,6 +155,7 @@ protected:
 
 signals:
 	void startDiveSiteEdit();
+	void showError(QString message);
 
 public
 slots:

desktop-widgets/notificationwidget.cpp

@@ -16,6 +16,11 @@ void NotificationWidget::showNotification(QString message, KMessageWidget::Messa
 	animatedShow();
 }
 
+void NotificationWidget::showError(QString message)
+{
+	showNotification(message, KMessageWidget::Error);
+}
+
 void NotificationWidget::hideNotification()
 {
 	animatedHide();

desktop-widgets/notificationwidget.h

@@ -21,6 +21,9 @@ public:
 	void hideNotification();
 	QString getNotificationText();
 
+public
+slots:
+	void showError(QString message);
 private:
 	QFutureWatcher<void> future_watcher;