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/*!+
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    \example network/ftp+
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    \title FTP Example+
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+
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    The FTP example demonstrates a simple FTP client that can be used+
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    to list the available files on an FTP server and download them.+
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+
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    \image ftp-example.png+
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+
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    The user of the example can enter the address or hostname of an+
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    FTP server in the \gui {Ftp Server} line edit, and then push the+
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    \gui Connect button to connect to it. A list of the server's+
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    top-level directory is then presented in the \gui {File List} tree+
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    view. If the selected item in the view is a file, the user can+
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    download it by pushing the \gui Download button. An item+
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    representing a directory can be double clicked with the mouse to+
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    show the contents of that directory in the view.+
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+
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    The functionality required for the example is implemented in the+
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    QFtp class, which provides an easy, high-level interface to the+
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    file transfer protocol. FTP operations are requested through+
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    \l{QFtp::Command}s. The operations are asynchronous. QFtp will+
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    notify us through signals when commands are started and finished.+
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+
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    We have one class, \c FtpWindow, which sets up the GUI and handles+
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    the FTP functionality. We will now go through its definition and+
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    implementation - focusing on the code concerning FTP. The code for+
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    managing the GUI is explained in other examples.+
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+
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    \section1 FtpWindow Class Definition+
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+
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    The \c FtpWindow class displays a window, in which the user can+
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    connect to and browse the contents of an FTP server. The slots of+
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    \c FtpWindow are connected to its widgets, and contain the+
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    functionality for managing the FTP connection. We also connect to+
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    signals in QFtp, which tells us when the+
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    \l{QFtp::Command}{commands} we request are finished, the progress+
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    of current commands, and information about files on the server.+
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+
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    \snippet examples/network/qftp/ftpwindow.h 0+
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+
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    We will look at each slot when we examine the \c FtpWindow+
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    implementation in the next section. We also make use of a few+
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    private variables:+
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+
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    \snippet examples/network/qftp/ftpwindow.h 1+
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+
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    The \c isDirectory hash keeps a history of all entries explored on+
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    the FTP server, and registers whether an entry represents a+
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    directory or a file. We use the QFile object to download files+
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    from the FTP server. +
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 +
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    \section1 FtpWindow Class Implementation+
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+
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    We skip the \c FtpWindow constructor as it only contains code for+
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    setting up the GUI, which is explained in other examples.+
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    +
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    We move on to the slots, starting with \c connectOrDisconnect().+
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+
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    \snippet examples/network/qftp/ftpwindow.cpp 0+
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+
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    If \c ftp is already pointing to a QFtp object, we QFtp::Close its+
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    FTP connection and delete the object it points to. Note that we do+
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    not delete the object using standard C++ \c delete as we need it+
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    to finish its abort operation.+
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+
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    \dots+
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    \snippet examples/network/qftp/ftpwindow.cpp 1+
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+
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    If we get here, \c connectOrDisconnect() was called to establish a+
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    new FTP connection. We create a new QFtp for our new connection,+
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    and connect its signals to slots in \c FtpWindow. The+
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    \l{QFtp::}{listInfo()} signal is emitted whenever information+
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    about a single file on the sever has been resolved. This signal is+
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    sent when we ask QFtp to \l{QFtp::}{list()} the contents of a+
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    directory. Finally, the \l{QFtp::}{dataTransferProgress()} signal+
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    is emitted repeatedly during an FTP file transfer, giving us+
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    progress reports.+
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+
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    \snippet examples/network/qftp/ftpwindow.cpp 2+
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+
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    The \gui {Ftp Server} line edit contains the IP address or+
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    hostname of the server to which we want to connect. We first check+
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    that the URL is a valid FTP sever address. If it isn't, we still+
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    try to connect using the plain text in \c ftpServerLineEdit. In+
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    either case, we assume that port \c 21 is used.+
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+
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    If the URL does not contain a user name and password, we use+
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    QFtp::login(), which will attempt to log into the FTP sever as an+
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    anonymous user. The QFtp object will now notify us when it has+
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    connected to the FTP server; it will also send a signal if it+
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    fails to connect or the username and password were rejected.+
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+
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    We move on to the \c downloadFile() slot:+
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+
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    \snippet examples/network/qftp/ftpwindow.cpp 3+
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    \dots+
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    \snippet examples/network/qftp/ftpwindow.cpp 4+
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    +
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    We first fetch the name of the file, which we find in the selected+
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    item of \c fileList. We then start the download by using+
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    QFtp::get(). QFtp will send progress signals during the download+
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    and a signal when the download is completed.  +
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+
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    \snippet examples/network/qftp/ftpwindow.cpp 5+
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+
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    QFtp supports canceling the download of files.+
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+
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    \snippet examples/network/qftp/ftpwindow.cpp 6+
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+
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    The \c ftpCommandFinished() slot is called when QFtp has+
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    finished a QFtp::Command. If an error occurred during the+
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    command, QFtp will set \c error to one of the values in+
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    the QFtp::Error enum; otherwise, \c error is zero.+
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    +
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    \snippet examples/network/qftp/ftpwindow.cpp 7+
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+
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    After login, the QFtp::list() function will list the top-level+
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    directory on the server. addToList() is connected to+
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    QFtp::listInfo(), and will be invoked for each entry in that+
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    directory.+
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+
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    \snippet examples/network/qftp/ftpwindow.cpp 8+
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+
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    When a \l{QFtp::}{Get} command is finished, a file has finished+
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    downloading (or an error occurred during the download).+
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    +
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    \snippet examples/network/qftp/ftpwindow.cpp 9+
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+
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    After a \l{QFtp::}{List} command is performed, we have to check if+
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    no entries were found (in which case our \c addToList() function+
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    would not have been called). +
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+
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    Let's continue with the \c addToList() slot:+
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+
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    \snippet examples/network/qftp/ftpwindow.cpp 10+
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+
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    When a new file has been resolved during a QFtp::List command,+
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    this slot is invoked with a QUrlInfo describing the file. We+
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    create a separate row for the file in \c fileList. If \c fileList+
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    does not have a current item, we set the new item to be the+
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    current item.+
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+
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    \snippet examples/network/qftp/ftpwindow.cpp 11+
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+
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    The \c processItem() slot is called when an item is double clicked+
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    in the \gui {File List}. If the item represents a directory, we+
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    want to load the contents of that directory with QFtp::list().+
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+
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    \snippet examples/network/qftp/ftpwindow.cpp 12+
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+
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    \c cdToParent() is invoked when the user requests to go to the+
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    parent directory of the one displayed in the file list. After+
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    changing the directory, we QFtp::List its contents.+
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+
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    \snippet examples/network/qftp/ftpwindow.cpp 13+
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+
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    The \c updateDataTransferProgress() slot is called regularly by+
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    QFtp::dataTransferProgress() when a file download is in progress.+
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    We use a QProgressDialog to show the download progression to the+
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    user.+
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+
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    \snippet examples/network/qftp/ftpwindow.cpp 14+
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+
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    The \c enableDownloadButton() is called whenever the current item+
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    in \c fileList changes. If the item represents a file, the \gui+
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    {Enable Download} Button should be enabled; otherwise, it is+
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    disabled.+
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*/+
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+
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