QDBusPendingReply Class

template <typename Types> class QDBusPendingReply

The QDBusPendingReply class contains the reply to an asynchronous method call. More...

Header: #include <QDBusPendingReply>
CMake: find_package(Qt6 COMPONENT Dbus)
target_link_libraries(mytarget PUBLIC Qt::Dbus)
qmake: QT += dbus
Inherits: QDBusPendingReplyBase

Public Types

enum anonymous { Count }

Public Functions

QDBusPendingReply(const QDBusMessage &message)
QDBusPendingReply(const QDBusPendingCall &call)
QDBusPendingReply(const QDBusPendingReply<Types...> &other)
QDBusPendingReply()
QDBusPendingReply<Types...> &operator=(const QDBusMessage &message)
QDBusPendingReply<Types...> &operator=(const QDBusPendingCall &call)
QDBusPendingReply<Types...> &operator=(const QDBusPendingReply<Types...> &other)
int count() const
typename Select<0>::Type value() const
void waitForFinished()

Detailed Description

The QDBusPendingReply is a template class with up to 8 template parameters. Those parameters are the types that will be used to extract the contents of the reply's data.

This class is similar in functionality to QDBusReply, but with two important differences:

  • QDBusReply accepts exactly one return type, whereas QDBusPendingReply can have from 1 to 8 types
  • QDBusReply only works on already completed replies, whereas QDBusPendingReply allows one to wait for replies from pending calls

Where with QDBusReply you would write:

 QDBusReply<QString> reply = interface->call("RemoteMethod");
 if (reply.isValid())
     // use the returned value
     useValue(reply.value());
 else
     // call failed. Show an error condition.
     showError(reply.error());

with QDBusPendingReply, the equivalent code (including the blocking wait for the reply) would be:

     QDBusPendingReply<QString> reply = iface->asyncCall("RemoteMethod");
     reply.waitForFinished();
     if (reply.isError())
         // call failed. Show an error condition.
         showErrorD(reply.error());
     else
         // use the returned value
         useValue(reply.value());

For method calls that have more than one output argument, with QDBusReply, you would write:

 reply = interface->call("RemoteMethod");

whereas with QDBusPendingReply, all of the output arguments should be template parameters:

     QDBusPendingReply<bool, QString> reply = iface->asyncCall("RemoteMethod");
     reply.waitForFinished();
     if (!reply.isError()) {
         if (reply.argumentAt<0>())
             showSuccess(reply.argumentAt<1>());
         else
             showFailure(reply.argumentAt<1>());
     }

QDBusPendingReply objects can be associated with QDBusPendingCallWatcher objects, which emit signals when the reply arrives.

See also QDBusPendingCallWatcher and QDBusReply.

Member Type Documentation

enum QDBusPendingReply::anonymous

ConstantValueDescription
QDBusPendingReply::Countstd::is_same_v<typename Select<0>::Type, void> ? 0 : sizeof...(Types)The number of arguments the reply is expected to have

Member Function Documentation

QDBusPendingReply::QDBusPendingReply(const QDBusMessage &message)

Creates a QDBusPendingReply object that will take its contents from the message message. In this case, this object will be already in its finished state and the reply's contents will be accessible.

See also isFinished().

QDBusPendingReply::QDBusPendingReply(const QDBusPendingCall &call)

Creates a QDBusPendingReply object that will take its contents from the call pending asynchronous call. This QDBusPendingReply object will share the same pending call reference as call.

QDBusPendingReply::QDBusPendingReply(const QDBusPendingReply<Types...> &other)

Creates a copy of the other QDBusPendingReply object. Just like QDBusPendingCall and QDBusPendingCallWatcher, this QDBusPendingReply object will share the same pending call reference. All copies share the same return values.

QDBusPendingReply::QDBusPendingReply()

Creates an empty QDBusPendingReply object. Without assigning a QDBusPendingCall object to this reply, QDBusPendingReply cannot do anything. All functions return their failure values.

QDBusPendingReply<Types...> &QDBusPendingReply::operator=(const QDBusMessage &message)

Makes this object take its contents from the message message and drops the reference to the current pending call. If the current reference is to an unfinished pending call and this is the last reference, the pending call will be canceled and there will be no way of retrieving the reply's contents, when they arrive.

After this function is finished, the QDBusPendingReply object will be in its "finished" state and the message contents will be accessible.

See also isFinished().

QDBusPendingReply<Types...> &QDBusPendingReply::operator=(const QDBusPendingCall &call)

Makes this object take its contents from the call pending call and drops the reference to the current pending call. If the current reference is to an unfinished pending call and this is the last reference, the pending call will be canceled and there will be no way of retrieving the reply's contents, when they arrive.

QDBusPendingReply<Types...> &QDBusPendingReply::operator=(const QDBusPendingReply<Types...> &other)

Makes a copy of other and drops the reference to the current pending call. If the current reference is to an unfinished pending call and this is the last reference, the pending call will be canceled and there will be no way of retrieving the reply's contents, when they arrive.

int QDBusPendingReply::count() const

Return the number of arguments the reply is supposed to have. This number matches the number of non-void template parameters in this class.

If the reply arrives with a different number of arguments (or with different types), it will be transformed into an error reply indicating a bad signature.

typename Select<0>::Type QDBusPendingReply::value() const

Returns the first argument in this reply, cast to type T1 (the first template parameter of this class). This is equivalent to calling argumentAt<0>().

This function is provided as a convenience, matching the QDBusReply::value() function.

Note that, if the reply hasn't arrived, this function causes the calling thread to block until the reply is processed.

If the reply is an error reply, this function returns a default-constructed T1 object, which may be indistinguishable from a valid value. To reliably determine whether the message was an error, use isError().

void QDBusPendingReply::waitForFinished()

Suspends the execution of the calling thread until the reply is received and processed. After this function returns, isFinished() should return true, indicating the reply's contents are ready to be processed.

See also QDBusPendingCallWatcher::waitForFinished().