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authorVenugopal Shivashankar <>2012-12-12 11:08:37 +0100
committerJerome Pasion <>2012-12-12 12:26:02 +0100
commite18df9add514a68d6aaaecd79c675519e648040b (patch)
parentf99365139c672d423c68197c2afa352cebb74885 (diff)
Doc: Added documentation for the qftp example
Change-Id: I40db57431cb4bbf2bb0185e8afa294bcaf2cb891 Reviewed-by: Jerome Pasion <>
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+** Copyright (C) 2012 Digia Plc and/or its subsidiary(-ies).
+** Contact:
+** This file is part of the documentation of the Qt Toolkit.
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and Digia. For licensing terms and
+** conditions see For further information
+** use the contact form at
+** GNU Free Documentation License Usage
+** Alternatively, this file may be used under the terms of the GNU Free
+** Documentation License version 1.3 as published by the Free Software
+** Foundation and appearing in the file included in the packaging of
+** this file. Please review the following information to ensure
+** the GNU Free Documentation License version 1.3 requirements
+** will be met:
+ \example network/qftp
+ \title FTP Example
+ The FTP example demonstrates a simple FTP client that can be used
+ to list the available files on an FTP server and download them.
+ \image ftp-example.png
+ The user of the example can enter the address or hostname of an
+ FTP server in the \gui {Ftp Server} line edit, and then push the
+ \gui Connect button to connect to it. A list of the server's
+ top-level directory is then presented in the \gui {File List} tree
+ view. If the selected item in the view is a file, the user can
+ download it by pushing the \gui Download button. An item
+ representing a directory can be double clicked with the mouse to
+ show the contents of that directory in the view.
+ The functionality required for the example is implemented in the
+ QFtp class, which provides an easy, high-level interface to the
+ file transfer protocol. FTP operations are requested through
+ \l{QFtp::Command}s. The operations are asynchronous. QFtp will
+ notify us through signals when commands are started and finished.
+ We have one class, \c FtpWindow, which sets up the GUI and handles
+ the FTP functionality. We will now go through its definition and
+ implementation - focusing on the code concerning FTP. The code for
+ managing the GUI is explained in other examples.
+ \section1 FtpWindow Class Definition
+ The \c FtpWindow class displays a window, in which the user can
+ connect to and browse the contents of an FTP server. The slots of
+ \c FtpWindow are connected to its widgets, and contain the
+ functionality for managing the FTP connection. We also connect to
+ signals in QFtp, which tells us when the
+ \l{QFtp::Command}{commands} we request are finished, the progress
+ of current commands, and information about files on the server.
+ \snippet examples/network/qftp/ftpwindow.h 0
+ We will look at each slot when we examine the \c FtpWindow
+ implementation in the next section. We also make use of a few
+ private variables:
+ \snippet examples/network/qftp/ftpwindow.h 1
+ The \c isDirectory hash keeps a history of all entries explored on
+ the FTP server, and registers whether an entry represents a
+ directory or a file. We use the QFile object to download files
+ from the FTP server.
+ \section1 FtpWindow Class Implementation
+ We skip the \c FtpWindow constructor as it only contains code for
+ setting up the GUI, which is explained in other examples.
+ We move on to the slots, starting with \c connectOrDisconnect().
+ \snippet examples/network/qftp/ftpwindow.cpp 0
+ If \c ftp is already pointing to a QFtp object, we QFtp::Close its
+ FTP connection and delete the object it points to. Note that we do
+ not delete the object using standard C++ \c delete as we need it
+ to finish its abort operation.
+ \dots
+ \snippet examples/network/qftp/ftpwindow.cpp 1
+ If we get here, \c connectOrDisconnect() was called to establish a
+ new FTP connection. We create a new QFtp for our new connection,
+ and connect its signals to slots in \c FtpWindow. The
+ \l{QFtp::}{listInfo()} signal is emitted whenever information
+ about a single file on the sever has been resolved. This signal is
+ sent when we ask QFtp to \l{QFtp::}{list()} the contents of a
+ directory. Finally, the \l{QFtp::}{dataTransferProgress()} signal
+ is emitted repeatedly during an FTP file transfer, giving us
+ progress reports.
+ \snippet examples/network/qftp/ftpwindow.cpp 2
+ The \gui {Ftp Server} line edit contains the IP address or
+ hostname of the server to which we want to connect. We first check
+ that the URL is a valid FTP sever address. If it isn't, we still
+ try to connect using the plain text in \c ftpServerLineEdit. In
+ either case, we assume that port \c 21 is used.
+ If the URL does not contain a user name and password, we use
+ QFtp::login(), which will attempt to log into the FTP sever as an
+ anonymous user. The QFtp object will now notify us when it has
+ connected to the FTP server; it will also send a signal if it
+ fails to connect or the username and password were rejected.
+ We move on to the \c downloadFile() slot:
+ \snippet examples/network/qftp/ftpwindow.cpp 3
+ \dots
+ \snippet examples/network/qftp/ftpwindow.cpp 4
+ We first fetch the name of the file, which we find in the selected
+ item of \c fileList. We then start the download by using
+ QFtp::get(). QFtp will send progress signals during the download
+ and a signal when the download is completed.
+ \snippet examples/network/qftp/ftpwindow.cpp 5
+ QFtp supports canceling the download of files. We make sure that
+ any file that is currently being written to is closed and removed,
+ and tidy up by deleting the file object.
+ \snippet examples/network/qftp/ftpwindow.cpp 6
+ The \c ftpCommandFinished() slot is called when QFtp has
+ finished a QFtp::Command. If an error occurred during the
+ command, QFtp will set \c error to one of the values in
+ the QFtp::Error enum; otherwise, \c error is zero.
+ \snippet examples/network/qftp/ftpwindow.cpp 7
+ After login, the QFtp::list() function will list the top-level
+ directory on the server. addToList() is connected to
+ QFtp::listInfo(), and will be invoked for each entry in that
+ directory.
+ \snippet examples/network/qftp/ftpwindow.cpp 8
+ When a \l{QFtp::}{Get} command is finished, a file has finished
+ downloading (or an error occurred during the download).
+ \snippet examples/network/qftp/ftpwindow.cpp 9
+ After a \l{QFtp::}{List} command is performed, we have to check if
+ no entries were found (in which case our \c addToList() function
+ would not have been called).
+ Let's continue with the \c addToList() slot:
+ \snippet examples/network/qftp/ftpwindow.cpp 10
+ When a new file has been resolved during a QFtp::List command,
+ this slot is invoked with a QUrlInfo describing the file. We
+ create a separate row for the file in \c fileList. If \c fileList
+ does not have a current item, we set the new item to be the
+ current item.
+ \snippet examples/network/qftp/ftpwindow.cpp 11
+ The \c processItem() slot is called when an item is double clicked
+ in the \gui {File List}. If the item represents a directory, we
+ want to load the contents of that directory with QFtp::list().
+ \snippet examples/network/qftp/ftpwindow.cpp 12
+ \c cdToParent() is invoked when the user requests to go to the
+ parent directory of the one displayed in the file list. After
+ changing the directory, we QFtp::List its contents.
+ \snippet examples/network/qftp/ftpwindow.cpp 13
+ The \c updateDataTransferProgress() slot is called regularly by
+ QFtp::dataTransferProgress() when a file download is in progress.
+ We use a QProgressDialog to show the download progression to the
+ user.
+ \snippet examples/network/qftp/ftpwindow.cpp 14
+ The \c enableDownloadButton() is called whenever the current item
+ in \c fileList changes. If the item represents a file, the \gui
+ {Enable Download} Button should be enabled; otherwise, it is
+ disabled.