Code clean and class constructor refactor.

src/device/DeviceManager.cpp

@@ -7,7 +7,6 @@
 #include <QVariant>
 #include <QTimerEvent>
 #include <QDate>
-#include <QDateTime>
 #include <qdebug.h>
 #include "appvals/AppGlobalValues.h"
 #include "json/ScanJson.h"

src/device/DeviceManager.h

@@ -15,6 +15,10 @@ public:
         static DeviceManager manager;
         return &manager;
     }
+    DeviceManager() = default;
+	~DeviceManager() override = default ;
+    DeviceManager(const DeviceManager&) = delete;
+    DeviceManager operator=(const DeviceManager&) = delete;
     /**
      * init device, include Shimlib and it's error call back,
      * deviceInfTimer to get temperature of water, and the
@@ -94,7 +98,7 @@ private:
 	bool previewing = false;
 	volatile bool endLoop = false;
 	bool errorOccurred = false;
-	QThread* previewDataCaller;
+	QThread* previewDataCaller = nullptr;
 };