c++ - Qt:没有这样的插槽 QObject::SlotName(QNetworkReply*)

Question

我是 QT 的新手，我正在尝试连接到 REST 服务并获取数据。我能够成功连接到我机器上的本地 tomcat，但出现找不到插槽的错误。请让我知道我可能做错了什么，我在 Qt 方面没有那么多专业知识，所以请耐心等待

人.cpp :

#include "person.h"
 #include <QNetworkRequest>
#include <QNetworkAccessManager>
#include<QObject>
#include<QDebug>
#include<QNetworkReply>

Person::Person()
{

}

Person::~Person()
{

}
void Person::addPerson (){


    QString url_str = "http://localhost:8080/";

    Person *person = new Person;
    person->setAccountStatus (true);
    person->setFirstName ("Akshay");
    person->setId (0);
    person->setPassword ("helloWorld");
    person->setUsername ("akshay@gmail.com");

    QNetworkAccessManager *manager = new QNetworkAccessManager();

    QObject object;
    object.connect(manager,SIGNAL(finished(QNetworkReply*)),SLOT(slotRequestFinished(QNetworkReply*)));
    QNetworkRequest request;
    request.setUrl (url_str);
    request.setHeader(QNetworkRequest::ContentTypeHeader,"application/json");
    QNetworkReply *reply = 0;
    manager->get(request);

void Person::slotRequestFinished(QNetworkReply *reply)
{
    qDebug()<<"Task finished";
}

人.h :

#ifndef PERSON_H
#define PERSON_H
#include<QString>
#include<QObject>
#include<QNetworkReply>

class Person
{
private:
     qint32 id;
     QString username;
     QString password;
     QString firstName;
     bool accountStatus;

public:
    Person();
    ~Person();

    qint32 getId() const;
    void setId(const qint32 &value);

    QString getUsername() const;
    void setUsername(const QString &value);

    QString getPassword() const;
    void setPassword(const QString &value);

    QString getFirstName() const;
    void setFirstName(const QString &value);

    bool getAccountStatus() const;
    void setAccountStatus(bool value);
    void addPerson();

public slots:
  void slotRequestFinished(QNetworkReply *reply);


protected:

    QList<Person> listPersons();


};

#endif // PERSON_H

}

我从 main.cpp 调用它:

Person *person = new Person;
person->addPerson ();

错误日志:

QML debugging is enabled. Only use this in a safe environment.
QObject::connect: No such slot QObject::slotRequestFinished(QNetworkReply*) in ../CheckNet/person.cpp:81
qt.network.ssl: QSslSocket: cannot resolve SSLv2_client_method
qt.network.ssl: QSslSocket: cannot resolve SSLv2_server_method

编辑:添加 QObject:

class Person : public QObject
{
    Q_OBJECT

private :
// values, getters and setters
}

当我执行上述操作时，出现以下错误:

/home/akshay/Qtprojects/CheckNet/person.cpp:57: error: undefined reference to `vtable for Person'
/home/akshay/Qtprojects/build-CheckNet-Desktop_Qt_5_4_1_GCC_64bit-Debug/person.o:-1: In function `Person::~Person()':

Answer 1

介绍

通过使用非静态成员函数 QObject::connect在新创建的 QObject(在您的代码段中名为 object)上，您实际上是在说所提供的 SLOT 是您所在对象的一部分当前正在调用成员函数。

QObject object;
object.connect(...);
    // ^- almost always wrong (deleteLater is the only slot in `QObject`)

根据上面的逻辑，我们可以很容易地看出您所描述的错误的原因； QObject 没有相关的插槽。

---

---

解决方案

您可以调用非静态 QObject::connect ，在真正具有所需 SLOT 的对象上采用三个参数(在您的情况下为 Person)。

_示例

// .- make sure `this` belongs to an object that inherits `QObject`
// v
   this->connect (
     manager, SIGNAL(finished(QNetworkReply*)), 
     SLOT(slotRequestFinished(QNetworkReply*))
   );

---

另一种选择是使用 QObject 中的 static 成员函数，其中第三个参数表示具有 SLOT 的对象:

^示例

QObject::connect (
  manager, SIGNAL(finished(QNetworkReply*)),
     this,   SLOT(slotRequestFinished(QNetworkReply*))
);

---

^{注意:上面的this表示一个Person类型的对象，需要的上下文在一个非静态成员中-Person 的函数，例如代码段中的 addPerson。}

^{注意:记住作为sender和receiver传递的对象必须继承自QObject， Person 目前没有。}