[Qt-qml] [QML]How judge QML Item exist?

[罗军]

Hi every one:

    There is a sample in Qt assistant. How judge "stopwatch" exist?

 class Stopwatch : public QObject
 {
     Q_OBJECT
 public:
     Stopwatch();

     Q_INVOKABLE bool isRunning() const;

 public slots:
     void start();
     void stop();

 private:
     bool m_running;
 };

 int main(int argc, char *argv[])
 {
     QApplication app(argc, argv);

     QDeclarativeView view;
     view.rootContext()->setContextProperty("stopwatch",
                                            new Stopwatch);

     view.setSource(QUrl::fromLocalFile("main.qml"));
     view.show();

     return app.exec();
 } import Qt 4.7

 Rectangle {
     width: 300
     height: 300

     MouseArea {
         anchors.fill: parent
         onClicked: {
             if (stopwatch.isRunning())
                 stopwatch.stop()
             else
                 stopwatch.start();
         }
     }
 }

Best regards.
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