Qt5错误：变量QQmlComponent组件有初始值但不完整

Question

我对Qt site的例子有一个问题，消息错误编译是：

这是错误：

error: variable 'QQmlComponent component' has initializer but incomplete type
     QQmlComponent component(&engine, QUrl::fromLocalFile("qml/untitled3/main.qml"));
                            ^

我的代码在这个post上是相似的，并且在这篇文章中进行了修正，但没有工作，我是新的使用qt 5.1 ......任何想法？。

我尝试添加库 #include <QQmlComponent> 要么 #include <QtQml/QQmlContext> 但是消息错误是一样的。

我的main.qml的路径是正确的：qml / untitled3 / main.qml

请帮帮我。

untitled3.pro

# Add more folders to ship with the application, here
folder_01.source = qml/untitled3
folder_01.target = qml
DEPLOYMENTFOLDERS = folder_01

# Additional import path used to resolve QML modules in Creator's code model
QML_IMPORT_PATH =

# If your application uses the Qt Mobility libraries, uncomment the following
# lines and add the respective components to the MOBILITY variable.
# CONFIG += mobility
# MOBILITY +=

# The .cpp file which was generated for your project. Feel free to hack it.
SOURCES += main.cpp

# Installation path
# target.path =

# Please do not modify the following two lines. Required for deployment.
include(qtquick2applicationviewer/qtquick2applicationviewer.pri)
qtcAddDeployment()

HEADERS += \
    message.h

message.h

#ifndef MESSAGE_H
#define MESSAGE_H
#include <QObject>
class Message : public QObject
{
Q_OBJECT
Q_PROPERTY(QString author READ author WRITE setAuthor NOTIFY authorChanged)
public:
    void setAuthor(const QString &a) {
        if (a != m_author) {
            m_author = a;
            emit authorChanged();
        }
    }
    QString author() const {
        return m_author;
    }
signals:
    void authorChanged();
private:
    QString m_author;
};
#endif

的main.cpp

#include <QtGui/QGuiApplication>
#include <QtQml/QQmlContext>
#include <QQmlEngine>
#include <QQmlComponent>
#include "message.h"


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

    QQmlEngine *engine = new QQmlEngine;
    Message msg;

    engine->rootContext()->setContextProperty("msg", &msg);
    QQmlComponent component(&engine, QUrl::fromLocalFile("qml/untitled3/main.qml"));
    component.create();



    return app.exec();
}