Qt 4.7: QCopChannel Class Reference

Qt Reference Documentation

# QCopChannel Class Reference

The QCopChannel class provides communication capabilities between clients in Qt for Embedded Linux. More...

     #include <QCopChannel>

Inherits: QObject.

- List of all members, including inherited members
- Qt 3 support members

## Public Functions

| QCopChannel ( const QString & channel, QObject * parent = 0 )
virtual | ~QCopChannel ()
QString | channel () const
virtual void | receive ( const QString & message, const QByteArray & data )

- 29 public functions inherited from QObject

## Signals

void | received ( const QString & message, const QByteArray & data )

- 1 signal inherited from QObject

## Static Public Members

bool | flush ()
bool | isRegistered ( const QString & channel )
bool | send ( const QString & channel, const QString & message, const QByteArray & data )
bool | send ( const QString & channel, const QString & message )

- 5 static public members inherited from QObject

### Additional Inherited Members

- 1 property inherited from QObject
- 1 public slot inherited from QObject
- 7 protected functions inherited from QObject

## Detailed Description

The QCopChannel class provides communication capabilities between clients in Qt for Embedded Linux.

Note that this class is only available in Qt for Embedded Linux.

The Qt COmmunication Protocol (QCOP) is a many-to-many protocol for transferring messages across registered channels. A channel is registered by name, and anyone who wants to can listen to the channel as well as send messages through it. The QCOP protocol allows clients to communicate both within the same address space and between different processes.

To send messages to a given channel, QCopChannel provides the static send() function. Using this function alone, the messages are queued until Qt re-enters the event loop. To immediately flush all queued messages to the registered listeners, call the static flush() function.

To listen to the traffic on a given channel, you typically instantiate a QCopChannel object for the given channel and connect to its received() signal that is emitted whenever there is incoming data. Use the static isRegistered() function to query the server for the existence of a given channel. QCopChannel provides the channel() function returning the name of this QCopChannel object's channel.

In additon, QCopChannel provides the virtual receive() function that can be reimplemented to filter the incoming messages and data. The default implementation simply emits the received() signal.

See also QWSServer, QWSClient, and Qt for Embedded Linux Architecture.

## Member Function Documentation

### QCopChannel::QCopChannel ( const QString & channel, QObject * parent = 0 )

Constructs a QCopChannel object for the specified channel, with the given parent. Once created, the channel is registered by the server.

See also isRegistered() and channel().

### QCopChannel::~QCopChannel ()`[virtual]`

Destroys this QCopChannel object.

The server is notified that this particular listener has closed its connection. The server will keep the channel open until the last registered listener detaches.

See also isRegistered() and channel().

### QString QCopChannel::channel () const

Returns the name of this object's channel.

See also isRegistered().

### bool QCopChannel::flush ()`[static]`

Flushes all queued messages to the registered listeners.

Note that this function returns false if no QApplication has been constructed, otherwise it returns true.

This function was introduced in Qt 4.2.

See also send().

### bool QCopChannel::isRegistered ( const QString & channel )`[static]`

Queries the server for the existence of the given channel. Returns true if the channel is registered; otherwise returns false.

See also channel() and send().

### void QCopChannel::receive ( const QString & message, const QByteArray & data )`[virtual]`

Processes the incoming message and data.

This function is called by the server when this object's channel receives new messages. Note that the default implementation simply emits the received() signal; reimplement this function to process the incoming message and data.

Note that the format of the given data has to be well defined in order to extract the information it contains. In addition, it is recommended to use the DCOP convention. This is not a requirement, but you must ensure that the sender and receiver agree on the argument types. For example:

     void MyClass::receive(const QString &message, const QByteArray &data)
     {
         QDataStream in(data);
         if (message == "execute(QString,QString)") {
             QString cmd;
             QString arg;
             in >> cmd >> arg;
             ...
         } else if (message == "delete(QString)") {
             QString fileName;
             in >> fileName;
             ...
         } else {
             ...
         }
     }

The above code assumes that the `message` is a DCOP-style function signature and the `data` contains the function's arguments.

See also send(), channel(), and received().

### void QCopChannel::received ( const QString & message, const QByteArray & data )`[signal]`

This signal is emitted whenever this object's channel receives new messages (i.e., it is emitted by the receive() function), passing the incoming message and data as parameters.

See also receive() and channel().

### bool QCopChannel::send ( const QString & channel, const QString & message, const QByteArray & data )`[static]`

Sends the given message on the specified channel with the given data. The message will be distributed to all clients subscribed to the channel. Returns true if the message is sent successfully; otherwise returns false.

It is recommended to use the DCOP convention. This is not a requirement, but you must ensure that the sender and receiver agree on the argument types.

Note that QDataStream provides a convenient way to fill the byte array with auxiliary data. For example:

     QByteArray data;
     QDataStream out(&data, QIODevice::WriteOnly);
     out << QString("cat") << QString("file.txt");
     QCopChannel::send("System/Shell", "execute(QString,QString)", data);

In the code above the channel is `"System/Shell"`. The `message` is an arbitrary string, but in the example we've used the DCOP convention of passing a function signature. Such a signature is formatted as `"functionname(types)"` where `types` is a list of zero or more comma-separated type names, with no whitespace, no consts and no pointer or reference marks, i.e. no "*" or "&".

See also receive() and isRegistered().

### bool QCopChannel::send ( const QString & channel, const QString & message )`[static]`

This is an overloaded function.