Question

我在主

中有以下代码

         QProcess process;
        QObject::connect(&process, &QProcess::error, [](QProcess::ProcessError error)
        {
            qDebug() << error;
        }, Qt::QueuedConnection);
        bool launched = process.startDetached("D:\temp.exe");

并在编译时生成此错误

    D:\main.cpp:5: error: C2665: 'QObject::connect' : none of the 3 overloads could convert all the argument types c:\qt\5.3\msvc2013_64\include\qtcore\qobject.h(205): could be 
'QMetaObject::Connection QObject::connect(const QObject *,const char
    *,const char *,Qt::ConnectionType) const' c:\qt\5.3\msvc2013_64\include\qtcore\qobject.h(201): or 
      'QMetaObject::Connection QObject::connect(const QObject *,const QMetaMethod &,const QObject *,const QMetaMethod &,Qt::ConnectionType)' c:\qt\5.3\msvc2013_64\include\qtcore\qobject.h(198): or      
 'QMetaObject::Connection QObject::connect(const QObject *,const char
    *,const QObject *,const char *,Qt::ConnectionType)' while trying to match the argument list '(QProcess *, overloaded-function, RunGUIMode::<lambda_5d6e7ee926a623cea2a0e4469253d55f>, Qt::ConnectionType)'

有人可以帮帮我，告诉我我做错了什么。

我想将QProcess类的信号连接到我的lambda

Answer 1

我不应该发布这个答案，但说实话它不是same question，它更复杂。

首先，为什么第一个版本不起作用。因为您无法提供receiver而无法使用其他参数（连接类型）。这意味着接下来是错误的。

connect(&process, static_cast<void (QProcess::*)(QProcess::ProcessError)>
        (&QProcess::error),[=](QProcess::ProcessError pError) {
        qWarning() << "error " << pError;
},Qt::QueuedConnection);

但接下来是正确的：

connect(&process, static_cast<void (QProcess::*)(QProcess::ProcessError)>
        (&QProcess::error), this , [=](QProcess::ProcessError pError) {
        qWarning() << "error " << pError;
},Qt::QueuedConnection);

如果您想知道原因，请查看qobject.h。我在此文件中进行了一些更改，只是为了更准确（不要更改此文件！）。

//first
//connect to a functor
template <typename Func1, typename Func2>
static inline typename QtPrivate::QEnableIf<QtPrivate::FunctionPointer<Func2>::ArgumentCount == -1, QMetaObject::Connection>::Type
connect(const typename QtPrivate::FunctionPointer<Func1>::Object *sender, Func1 signal, Func2 slot)
{
    qDebug("There is no here argument for connection, isn't it?");
    return connect(sender, signal, sender, slot, Qt::DirectConnection);
}

//second
//connect to a functor, with a "context" object defining in which event loop is going to be executed
template <typename Func1, typename Func2>
static inline typename QtPrivate::QEnableIf<QtPrivate::FunctionPointer<Func2>::ArgumentCount == -1, QMetaObject::Connection>::Type
connect(const typename QtPrivate::FunctionPointer<Func1>::Object *sender, Func1 signal, const QObject *context, Func2 slot,
        Qt::ConnectionType type = Qt::AutoConnection)
{
    qDebug("This will be called, and as you can see you need specify the context if you want to use connection type.");
    //...

其次，当您运行此代码时，您将获得：

QObject :: connect：无法对类型的参数进行排队＆＃39;另外，QProcess ::的processError＆＃39; （确保＆＃39; QProcess :: ProcessError＆＃39;是使用qRegisterMetaType（）注册。）

所以你需要在连接之前添加qRegisterMetaType<QProcess::ProcessError>("QProcess::ProcessError");。

所以最终版本是：

qRegisterMetaType<QProcess::ProcessError>("QProcess::ProcessError");
QProcess process;
connect(&process, static_cast<void (QProcess::*)(QProcess::ProcessError)>
        (&QProcess::error), this , [=](QProcess::ProcessError pError) {
    qWarning() << "error " << pError;
},Qt::QueuedConnection);
process.start("MyProgram");
bool launched = process.startDetached("example");

C2665：'QObject :: connect'：3个重载中没有一个可以转换所有参数类型

1 个答案: