c++ - QT C++ - 信号和槽 : "No such slot QLabel..." even the SLOT function is existing in my class

Question

所以我正在尝试使用 C++ 学习 Qt Framework。我正在了解信号​​和插槽，但我很难创建自定义插槽。因此，当我按照一些教程进行操作时，我的程序出现了以下错误:

QObject::connect: No such slot QLabel::updateMessage() in main.cpp:28

updateMessage() 在我的Test 类中被声明为一个public slot

以下是我的代码的一些片段:

测试.h

class Test : public QObject
{
    Q_OBJECT
public:
    Test(void);
    ~Test(void);
    void setMessage(char *tMsg);
    char* getMessage();

    QWidget *window;
    QGridLayout *layout;
    QLabel *lblMsg;
    QPushButton *btnShow;


public slots:
    void updateMessage();

private:
    char msg[80];
    QString str;

};

main.cpp

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    Test t;
    t.window->setWindowTitle("Testing Qt");
    t.window->setLayout(t.layout);
    t.window->show();
    return app.exec();
}

Test::Test(void)
{
    window = new QWidget;
    lblMsg = new QLabel;
    btnShow = new QPushButton("Show message");

    connect(btnShow,SIGNAL(clicked()),lblMsg,SLOT(updateMessage()));
    layout = new QGridLayout;
    layout->addWidget(lblMsg);
    layout->addWidget(btnShow);

    char str1[] = "Hello, Qt World!";
    setMessage(str1);
}


Test::~Test(void)
{

}

void Test::setMessage(char *tMsg)
{
    memcpy(msg, tMsg, sizeof(msg));
}

char* Test::getMessage()
{
    return msg;
}

void Test::updateMessage()
{
    string strMsg(getMessage());
    QString qstr = QString::fromStdString(strMsg);
    lblMsg->setText(qstr);
    delete msg;
}

HelloQtWorld.pro

######################################################################
# Automatically generated by qmake (3.0) Tue Nov 15 00:30:22 2016
######################################################################

TEMPLATE = app
TARGET = HelloQtWorld
INCLUDEPATH += .

# Input
HEADERS += stdafx.h Test.h
SOURCES += anotherClass.cpp \
           main.cpp \
           stdafx.cpp \
           GeneratedFiles/qrc_helloqtworld.cpp
RESOURCES += helloqtworld.qrc

也有人可以尝试为我解释信号和槽是如何工作的吗？先感谢您。 :)

Answer 1

问题出在这一行:

connect(btnShow,SIGNAL(clicked()),lblMsg,SLOT(updateMessage()));

您正在连接 QLabel 的槽，而不是您类(class)的槽。

这里应该改成

connect(btnShow,SIGNAL(clicked()),this,SLOT(updateMessage()));

注意信号和槽的新 Qt 5 语法。