Fix a UI block bug.

src/device/DeviceManager.h

@@ -6,6 +6,7 @@
 #define GUI_DEVICEMANAGER_H
 
 #include <QObject>
+#include <QThread>
 class DeviceManager:public QObject {
     Q_OBJECT
 
@@ -25,7 +26,9 @@ private:
     int deviceInfTimerID = -1;
     int lastStatus=-1;
     bool previewing = false;
+    bool endLoop = false;
     bool errorOccured = false;
+    QThread* previewDataCaller;
 };