- Qt 6.8
- Qt D-Bus
- C++ Classes
- QDBusMessage
- Qt 6.8.3 Reference Documentation

# QDBusMessage Class

The QDBusMessage class represents one message sent or received over the D-Bus bus. More...

Header: | `#include <QDBusMessage>`
CMake: | `find_package(Qt6 REQUIRED COMPONENTS DBus)` `target_link_libraries(mytarget PRIVATE Qt6::DBus)`
qmake: | `QT += dbus`

- List of all members, including inherited members

## Public Types

enum | MessageType { MethodCallMessage, SignalMessage, ReplyMessage, ErrorMessage, InvalidMessage }

## Public Functions

| QDBusMessage()
| QDBusMessage(const QDBusMessage &other)
| ~QDBusMessage()
QList<QVariant> | arguments() const
bool | autoStartService() const
QDBusMessage | createErrorReply(const QDBusError &error) const
QDBusMessage | createErrorReply(QDBusError::ErrorType type, const QString &msg) const
QDBusMessage | createErrorReply(const QString &name, const QString &msg) const
QDBusMessage | createReply(const QList<QVariant> &arguments = QList<QVariant>()) const
QDBusMessage | createReply(const QVariant &argument) const
QString | errorMessage() const
QString | errorName() const
QString | interface() const
bool | isDelayedReply() const
bool | isInteractiveAuthorizationAllowed() const
bool | isReplyRequired() const
QString | member() const
QString | path() const
QString | service() const
void | setArguments(const QList<QVariant> &arguments)
void | setAutoStartService(bool enable)
void | setDelayedReply(bool enable) const
void | setInteractiveAuthorizationAllowed(bool enable)
QString | signature() const
void | swap(QDBusMessage &other)
QDBusMessage::MessageType | type() const
QDBusMessage & | operator<<(const QVariant &arg)
QDBusMessage & | operator=(const QDBusMessage &other)

## Static Public Members

QDBusMessage | createError(const QDBusError &error)
QDBusMessage | createError(QDBusError::ErrorType type, const QString &msg)
QDBusMessage | createError(const QString &name, const QString &msg)
QDBusMessage | createMethodCall(const QString &service, const QString &path, const QString &interface, const QString &method)
QDBusMessage | createSignal(const QString &path, const QString &interface, const QString &name)
QDBusMessage | createTargetedSignal(const QString &service, const QString &path, const QString &interface, const QString &name)

## Detailed Description

This object can represent any of the four different types of messages (MessageType) that can occur on the bus:

- Method calls
- Method return values
- Signal emissions
- Error codes

Objects of this type are created with the static createError(), createMethodCall() and createSignal() functions. Use the QDBusConnection::send() function to send the messages.

## Member Type Documentation

### enum QDBusMessage::MessageType

The possible message types:

Constant | Value | Description
--- | --- | ---
`QDBusMessage::MethodCallMessage` | `1` | a message representing an outgoing or incoming method call
`QDBusMessage::SignalMessage` | `4` | a message representing an outgoing or incoming signal emission
`QDBusMessage::ReplyMessage` | `2` | a message representing the return values of a method call
`QDBusMessage::ErrorMessage` | `3` | a message representing an error condition in response to a method call
`QDBusMessage::InvalidMessage` | `0` | an invalid message: this is never set on messages received from D-Bus

## Member Function Documentation

### QDBusMessage::QDBusMessage()

Constructs an empty, invalid QDBusMessage object.

See also createError(), createMethodCall(), and createSignal().

### QDBusMessage::QDBusMessage(const QDBusMessage &other)

Constructs a copy of the object given by other.

Note: QDBusMessage objects are shared. Modifications made to the copy will affect the original one as well. See setDelayedReply() for more information.

### `[noexcept]` QDBusMessage::~QDBusMessage()

Disposes of the object and frees any resources that were being held.

### QList<QVariant> QDBusMessage::arguments() const

Returns the list of arguments that are going to be sent or were received from D-Bus.

See also setArguments().

### bool QDBusMessage::autoStartService() const

Returns the auto start flag, as set by setAutoStartService(). By default, this flag is true, which means Qt D-Bus will auto start a service, if it is not running already.

See also setAutoStartService().

### `[static]` QDBusMessage QDBusMessage::createError(const QDBusError &error)

Constructs a new DBus message representing the given error.

### `[static]` QDBusMessage QDBusMessage::createError(QDBusError::ErrorType type, const QString &msg)

Constructs a new DBus message for the error type type using the message msg. Returns the DBus message.

### `[static]` QDBusMessage QDBusMessage::createError(const QString &name, const QString &msg)

Constructs a new DBus message representing an error, with the given name and msg.

### QDBusMessage QDBusMessage::createErrorReply(const QDBusError &error) const

Constructs a new DBus message representing an error reply message, from the given error object.

### QDBusMessage QDBusMessage::createErrorReply(QDBusError::ErrorType type, const QString &msg) const

Constructs a new DBus reply message for the error type type using the message msg. Returns the DBus message.

### QDBusMessage QDBusMessage::createErrorReply(const QString &name, const QString &msg) const

Constructs a new DBus message representing an error reply message, with the given name and msg.

### `[static]` QDBusMessage QDBusMessage::createMethodCall(const QString &service, const QString &path, const QString &interface, const QString &method)

Constructs a new DBus message representing a method call. A method call always informs its destination address (service, path, interface and method).

The DBus bus allows calling a method on a given remote object without specifying the destination interface, if the method name is unique. However, if two interfaces on the remote object export the same method name, the result is undefined (one of the two may be called or an error may be returned).

When using DBus in a peer-to-peer context (i.e., not on a bus), the service parameter is optional.

The QDBusInterface class provides a simpler abstraction to synchronous method calling.

This function returns a QDBusMessage object that can be sent with QDBusConnection::call().

### QDBusMessage QDBusMessage::createReply(const QList<QVariant> &arguments = QList<QVariant>()) const

Constructs a new DBus message representing a reply, with the given arguments.

### QDBusMessage QDBusMessage::createReply(const QVariant &argument) const

Constructs a new DBus message representing a reply, with the given argument.

### `[static]` QDBusMessage QDBusMessage::createSignal(const QString &path, const QString &interface, const QString &name)

Constructs a new DBus message with the given path, interface and name, representing a signal emission.

A DBus signal is emitted from one application and is received by all applications that are listening for that signal from that interface.

The QDBusMessage object that is returned can be sent using the QDBusConnection::send() function.

### `[static]` QDBusMessage QDBusMessage::createTargetedSignal(const QString &service, const QString &path, const QString &interface, const QString &name)

Constructs a new DBus message with the given path, interface and name, representing a signal emission to a specific destination.

A DBus signal is emitted from one application and is received only by the application owning the destination service name.

The QDBusMessage object that is returned can be sent using the QDBusConnection::send() function.

### QString QDBusMessage::errorMessage() const

Returns the human-readable message associated with the error that was received.

### QString QDBusMessage::errorName() const

Returns the name of the error that was received.

### QString QDBusMessage::interface() const

Returns the interface of the method being called (in the case of a method call) or of the signal being received from.

### bool QDBusMessage::isDelayedReply() const

Returns the delayed reply flag, as set by setDelayedReply(). By default, this flag is false, which means Qt D-Bus will generate automatic replies when necessary.

### bool QDBusMessage::isInteractiveAuthorizationAllowed() const

Returns whether the message has the `ALLOW_INTERACTIVE_AUTHORIZATION` flag set.

See also setInteractiveAuthorizationAllowed() and QDBusAbstractInterface::isInteractiveAuthorizationAllowed().

### bool QDBusMessage::isReplyRequired() const

Returns the flag that indicates if this message should see a reply or not. This is only meaningful for method call messages: any other kind of message cannot have replies and this function will always return false for them.

### QString QDBusMessage::member() const

Returns the name of the signal that was emitted or the name of the method that was called.

### QString QDBusMessage::path() const

Returns the path of the object that this message is being sent to (in the case of a method call) or being received from (for a signal).

### QString QDBusMessage::service() const

Returns the name of the service or the bus address of the remote method call.

### void QDBusMessage::setArguments(const QList<QVariant> &arguments)

Sets the arguments that are going to be sent over D-Bus to arguments. Those will be the arguments to a method call or the parameters in the signal.

See also arguments().

### void QDBusMessage::setAutoStartService(bool enable)

Sets the auto start flag to enable. This flag only makes sense for method call messages, where it tells the D-Bus server to either auto start the service responsible for the service name, or not to auto start it.

By default this flag is true, i.e. a service is autostarted. This means:

When the service that this method call is sent to is already running, the method call is sent to it. If the service is not running yet, the D-Bus daemon is requested to autostart the service that is assigned to this service name. This is handled by .service files that are placed in a directory known to the D-Bus server. These files then each contain a service name and the path to a program that should be executed when this service name is requested.

See also autoStartService().

### void QDBusMessage::setDelayedReply(bool enable) const

Sets whether the message will be replied later (if enable is true) or if an automatic reply should be generated by Qt D-Bus (if enable is false).

In D-Bus, all method calls must generate a reply to the caller, unless the caller explicitly indicates otherwise (see isReplyRequired()). QtDBus automatically generates such replies for any slots being called, but it also allows slots to indicate whether they will take responsibility of sending the reply at a later time, after the function has finished processing.

See also isDelayedReply() and Delayed Replies.

### void QDBusMessage::setInteractiveAuthorizationAllowed(bool enable)

Enables or disables the `ALLOW_INTERACTIVE_AUTHORIZATION` flag in a message.

This flag only makes sense for method call messages (QDBusMessage::MethodCallMessage). If enable is set to `true`, the flag indicates to the callee that the caller of the method is prepared to wait for interactive authorization to take place (for instance via Polkit) before the actual method is processed.

If enable is set to `false`, the flag is not set, meaning that the other end is expected to make any authorization decisions non-interactively and promptly. This is the default.

The `org.freedesktop.DBus.Error.InteractiveAuthorizationRequired` error indicates that authorization failed, but could have succeeded if this flag had been set.

See also isInteractiveAuthorizationAllowed() and QDBusAbstractInterface::setInteractiveAuthorizationAllowed().

### QString QDBusMessage::signature() const

Returns the signature of the signal that was received or for the output arguments of a method call.

### `[noexcept]` void QDBusMessage::swap(QDBusMessage &other)

Swaps this message with other. This operation is very fast and never fails.

### QDBusMessage::MessageType QDBusMessage::type() const

Returns the message type.

### QDBusMessage &QDBusMessage::operator<<(const QVariant &arg)

Appends the argument arg to the list of arguments to be sent over D-Bus in a method call or signal emission.

### QDBusMessage &QDBusMessage::operator=(const QDBusMessage &other)

Copies the contents of the object given by other.

Note: QDBusMessage objects are shared. Modifications made to the copy will affect the original one as well. See setDelayedReply() for more information.