PrintView improvements (#250)

- Allow printer selection directly from PrintView
- Print button bypasses the system print dialog, since label printing is quite different from typical printing tasks
- Separate button to optionally use system print dialog, if needed

glabels/PrinterMonitor.cpp

@@ -0,0 +1,88 @@
+/*  PrinterMonitor.cpp
+ *
+ *  Copyright (C) 2025  Jaye Evins <evins@snaught.com>
+ *
+ *  This file is part of gLabels-qt.
+ *
+ *  gLabels-qt is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  gLabels-qt is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with gLabels-qt.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+
+#include "PrinterMonitor.h"
+
+#include <QPrinterInfo>
+#include <QDebug>
+
+
+namespace glabels
+{
+
+	///
+	/// Static data
+	///
+	std::unique_ptr<PrinterMonitor> PrinterMonitor::mInstance;
+
+
+	///
+	/// Constructor
+	///
+	PrinterMonitor::PrinterMonitor()
+	{
+		mCurrentAvailablePrinters = QPrinterInfo::availablePrinterNames();
+
+		mTimer.reset( new QTimer( this ) );
+		connect( mTimer.get(), SIGNAL(timeout()), this, SLOT(onTimerTimeout()) );
+		mTimer->start( 1000 );
+	}
+
+
+	///
+	/// Get singleton instance
+	///
+	PrinterMonitor* PrinterMonitor::instance()
+	{
+		if ( !mInstance )
+		{
+			mInstance.reset( new PrinterMonitor() );
+		}
+
+		return mInstance.get();
+	}
+
+
+	///
+	/// Get available printers
+	///
+	const QStringList& PrinterMonitor::availablePrinters() const
+	{
+		return mCurrentAvailablePrinters;
+	}
+
+
+	///
+	/// On timer timeout
+	///
+	void PrinterMonitor::onTimerTimeout()
+	{
+		auto newAvailablePrinters = QPrinterInfo::availablePrinterNames();
+		if ( newAvailablePrinters != mCurrentAvailablePrinters )
+		{
+			mCurrentAvailablePrinters = newAvailablePrinters;
+
+			emit availablePrintersChanged( mCurrentAvailablePrinters );
+		}
+	}
+
+	
+} // namespace glabels