added stringchangewatcher class

stringchangewatcher.h

@@ -0,0 +1,30 @@
+#ifndef STRINGCHANGEWATCHER_H
+#define STRINGCHANGEWATCHER_H
+
+#include <QObject>
+
+class stringChangeWatcher : public QObject
+{
+    Q_OBJECT
+    Q_PROPERTY( QString value READ getValue WRITE setValue NOTIFY valueChanged )
+public:
+    explicit stringChangeWatcher( QObject* parent = nullptr ) :
+        QObject{ parent }, str{ "" } {}
+    virtual ~stringChangeWatcher() {}
+
+    QString getValue() const { return str; }
+public slots:
+    void setValue( QString value )
+    {
+        if ( value != str ) {
+            str = value;
+            emit valueChanged( str );
+        }
+    }
+signals:
+    void valueChanged( QString value );
+private:
+    QString str;
+
+};
+#endif // STRINGCHANGEWATCHER_H