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/*!

    \example tools/customcompleter

    \title Custom Completer Example

    The Custom Completer example shows how to provide string-completion

    facilities for an input widget based on data provided by a model. The

    completer pops up suggestions for possible words based on the first three

    characters input by the user and the user's choice of word is inserted

    into the \c TextEdit using QTextCursor.

    \image customcompleter-example.png

    \section1 Setting Up The Resource File

    The Custom Completer example requires a resource file, \e wordlist.txt,

    that has a list of words to help QCompleter complete words. This file

    contains the following:

    \quotefile examples/tools/customcompleter/customcompleter.qrc

    \section1 TextEdit Class Definition

    The \c TextEdit class is a subclass of QTextEdit with a custom

    \c insertCompletion() slot and it reimplements the

    \l{QAbstractScrollArea::keyPressEvent()}{keyPressEvent()} and the

    \l{QWidget::focusInEvent()}{focusInEvent()} functions. \c TextEdit also

    contains a private function \c textUnderCursor() and a private instance

    of QCompleter, \c c.

    \snippet examples/tools/customcompleter/textedit.h 0

    \section1 TextEdit Class Implementation

    The constructor for \c TextEdit constructs a \c TextEdit with a parent and

    initializes \c c. The instructions to use the completer is displayed on

    the \c TextEdit object, using the

    \l{QTextEdit::setPlainText()}{setPlainText()} function.

    \snippet examples/tools/customcompleter/textedit.cpp 0

    In addition, \c TextEdit also includes a default destructor:

    \snippet examples/tools/customcompleter/textedit.cpp 1

    The \c setCompleter() function accepts a \a completer and sets it up.

    We use \c{if (c)} to check if \c c has been initialized. If it has been

    initialized, the QObject::disconnect() function is invoked to disconnect

    the signal from the slot. This is to ensure that no previous completer

    object is still connected to the slot.

    \snippet examples/tools/customcompleter/textedit.cpp 2

    We then instantiate \c c with \a completer and set it as \c{TextEdit}'s

    widget. The completion mode and case sensitivity are also set and then

    we connect the \l{QCompleter::activated()}{activated()} signal to the

    \c insertCompletion() slot.

    The \c completer() function is a getter function that returns \c c.

    \snippet examples/tools/customcompleter/textedit.cpp 3

    The completer pops up the options available, based on the contents of

    \e wordlist.txt, but the text cursor is responsible for filling in the

    missing characters, according to the user's choice of word.

    Suppose the user inputs "ACT" and accepts the completer's suggestion of

    "ACTUAL". The \c completion string is then sent to \c insertCompletion()

    by the completer's \l{QCompleter::activated()}{activated()} signal.

    The \c insertCompletion() function is responsible for completing the word

    using a QTextCursor object, \c tc. It validates to ensure that the

    completer's widget is \c TextEdit before using \c tc to insert the extra

    characters to complete the word.

    \snippet examples/tools/customcompleter/textedit.cpp 4

    The figure below illustrates this process:

    \image customcompleter-insertcompletion.png

    \c{completion.length()} = 6

    \c{c->completionPrefix().length()}=3

    The difference between these two values is \c extra, which is 3. This

    means that the last three characters from the right, "U", "A", and "L",

    will be inserted by \c tc.

    The \c textUnderCursor() function uses a QTextCursor, \c tc, to select a

    word under the cursor and return it.

    \snippet examples/tools/customcompleter/textedit.cpp 5

    The \c TextEdit class reimplements \l{QWidget::focusInEvent()}

    {focusInEvent()} function, which is an event handler used to receive

    keyboard focus events for the widget.

    \snippet examples/tools/customcompleter/textedit.cpp 6

    The \l{QAbstractScrollArea::keyPressEvent()}{keyPressEvent()} is

    reimplemented to ignore key events like Qt::Key_Enter, Qt::Key_Return,

    Qt::Key_Escape, Qt::Key_Tab, and Qt::Key_Backtab so the completer can

    handle them.

    If there is an active completer, we cannot process the shortcut, Ctrl+E.

    \snippet examples/tools/customcompleter/textedit.cpp 7

    We also handle other modifiers and shortcuts for which we do not want the

    completer to respond to.

    \snippet examples/tools/customcompleter/textedit.cpp 8

    Finally, we pop up the completer.

    \section1 MainWindow Class Definition

    The \c MainWindow class is a subclass of QMainWindow and implements a

    private slot, \c about(). This class also has two private functions,

    \c createMenu() and \c modelFromFile() as well as private instances of

    QCompleter and \c TextEdit.

    \snippet examples/tools/customcompleter/mainwindow.h 0

    \section1 MainWindow Class Implementation

    The constructor constructs a \c MainWindow with a parent and initializes

    the \c completer. It also instantiates a \c TextEdit and sets its

    completer. A QStringListModel, obtained from \c modelFromFile(), is used

    to populate the \c completer. The \c{MainWindow}'s central widget is set

    to \c TextEdit and its size is set to 500 x 300.

    \snippet examples/tools/customcompleter/mainwindow.cpp 0

    The \c createMenu() function creates the necessary QAction objects needed

    for the "File" and "Help" menu and their \l{QAction::triggered()}

    {triggered()} signals are connected to the \c quit(), \c about(), and

    \c aboutQt() slots respectively.

    \snippet examples/tools/customcompleter/mainwindow.cpp 1

    The \c modelFromFile() function accepts a \a fileName and attempts to

    extract the contents of this file into a QStringListModel. We display the

    Qt::WaitCursor when we are populating the QStringList, \c words, and

    restore the mouse cursor when we are done.

    \snippet examples/tools/customcompleter/mainwindow.cpp 2

    The \c about() function provides a brief description about the Custom

    Completer example.

    \snippet examples/tools/customcompleter/mainwindow.cpp 3

    \section1 \c main() Function

    The \c main() function instantiates \c MainWindow and invokes the

    \l{QWidget::show()}{show()} function.

    \snippet examples/tools/customcompleter/main.cpp 0

*/