c++ - Qt: connect() 需要至少 4 个参数，但提供了 2 个

Question

我在这里错过了什么，为什么下面的例子给我编译时错误？

测试线.h:

#include <QLineEdit>
class TestLine : public QLineEdit
{
    Q_OBJECT
public:
    TestLine(QWidget *parent = 0);
public slots:
    virtual void on_textEdited(const QString&);
};

测试线.cpp:

#include "testline.h"
TestLine::TestLine(QWidget *parent) : QLineEdit(parent)
{
    connect(this, SIGNAL(textEdited(const QString &))), this,
            SLOT(on_textEdited(const QString &)));
}

void TestLine::on_textEdited(const QString &text)
{
   // something
}

错误信息:

../testline.cpp:7:5: error

: no matching member function for call to 'connect'
    connect(this, SIGNAL(textEdited(const QString &))), this,
    ^~~~~~~
../../../Qt/5.7/clang_64/lib/QtCore.framework/Headers/qobject.h:219:43: note: candidate function template not viable: requires at least 4 arguments, but 2 were provided

Answer 1

connect(this, SIGNAL(textEdited(const QString &)))
//     1            2          3               321

此时您所做的正是编译器输出所说的 - 您仅使用 2 个参数调用 connect()。