Allow running only one instance of application.

application/application.cpp

@@ -0,0 +1,31 @@
+#include "application.h"
+
+Application::Application(int &argc, char **argv)
+    :QApplication(argc, argv)
+{
+    m_single = new QSharedMemory("ShredMemoryForOneInstanceOfProdejnaApp", this);
+}
+
+Application::~Application()
+{
+    if (m_single->isAttached())
+    {
+        m_single->detach();
+    }
+}
+
+bool Application::lock()
+{
+    if (m_single->attach(QSharedMemory::ReadOnly))
+    {
+        m_single->detach();
+        return false;
+    }
+
+    if (m_single->create(1))
+    {
+        return true;
+    }
+
+    return false;
+}