qtbase/examples/widgets/doc/src/completer.qdoc

// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only

/*!
    \example tools/completer
    \title Completer Example
    \examplecategory {User Interface Components}
    \ingroup examples-widgets-tools

    \brief The Completer example shows how to provide string-completion facilities
    for an input widget based on data provided by a model.

    \image completer-example.png

    This example uses a custom item model, \c FileSystemModel, and a QCompleter object.
    QCompleter is a class that provides completions based on an item model. The
    type of model, the completion mode, and the case sensitivity can be
    selected using combo boxes.

    \section1 The Resource File

    The Completer example requires a resource file in order to store the
    \e{countries.txt} and \e{words.txt}. The resource file contains the
    following code:

    \quotefile tools/completer/completer.qrc

    \section1 FileSystemModel Class Definition

    The \c FileSystemModel class is a subclass of QFileSystemModel, which provides a data
    model for the local filesystem.

    \snippet tools/completer/fsmodel.h 0

    This class only has a constructor and a \c data() function as it is only
    created to enable \c data() to return the entire file path for the
    display role, unlike \l{QFileSystemModel}'s \c data() function that only returns
    the folder and not the drive label. This is further explained in
    \c FileSystemModel's implementation.

    \section1 FileSystemModel Class Implementation

    The constructor for the \c FileSystemModel class is used to pass \a parent to
    QFileSystemModel.

    \snippet tools/completer/fsmodel.cpp 0

    As mentioned earlier, the \c data() function is reimplemented in order to
    get it to return the entire file path for the display role. For example,
    with a QFileSystemModel, you will see "Program Files" in the view. However, with
    \c FileSystemModel, you will see "C:\\Program Files".

    \snippet tools/completer/fsmodel.cpp 1

    The Qt::EditRole, which QCompleter uses to look for matches, is left
    unchanged.

    \section1 MainWindow Class Definition

    The \c MainWindow class is a subclass of QMainWindow and implements five
    private slots - \c about(), \c changeCase(), \c changeMode(), \c changeModel(),
    and \c changeMaxVisible().

    \snippet tools/completer/mainwindow.h 0

    Within the \c MainWindow class, we have two private functions:
    \c createMenu() and \c modelFromFile(). We also declare the private widgets
    needed - three QComboBox objects, a QCheckBox, a QCompleter, a QLabel, and
    a QLineEdit.

    \snippet tools/completer/mainwindow.h 1

    \section1 MainWindow Class Implementation

    The constructor of \c MainWindow constructs a \c MainWindow with a parent
    widget and initializes the private members. The \c createMenu() function
    is then invoked.

    We set up three QComboBox objects, \c modelComb, \c modeCombo and
    \c caseCombo. By default, the \c modelCombo is set to QFileSystemModel,
    the \c modeCombo is set to "Filtered Popup" and the \c caseCombo is set
    to "Case Insensitive".

    \snippet tools/completer/mainwindow.cpp 0

    The \c maxVisibleSpinBox is created and determines the number of visible
    item in the completer

    The \c wrapCheckBox is then set up. This \c checkBox determines if the
    \c{completer}'s \l{QCompleter::setWrapAround()}{setWrapAround()} property
    is enabled or disabled.

    \snippet tools/completer/mainwindow.cpp 1

    We instantiate \c contentsLabel and set its size policy to
    \l{QSizePolicy::Fixed}{fixed}. The combo boxes' \l{QComboBox::activated()}
    {activated()} signals are then connected to their respective slots.

    \snippet tools/completer/mainwindow.cpp 2

    The \c lineEdit is set up and then we arrange all the widgets using a
    QGridLayout. The \c changeModel() function is called, to initialize the
    \c completer.

    \snippet tools/completer/mainwindow.cpp 3

    The \c createMenu() function is used to instantiate the QAction objects
    needed to fill the \c fileMenu and \c helpMenu. The actions'
    \l{QAction::triggered()}{triggered()} signals are connected to their
    respective slots.

    \snippet tools/completer/mainwindow.cpp 4

    The \c modelFromFile() function accepts the \a fileName of a file and
    processes it depending on its contents.

    We first validate the \c file to ensure that it can be opened in
    QFile::ReadOnly mode. If this is unsuccessful, the function returns an
    empty QStringListModel.

    \snippet tools/completer/mainwindow.cpp 5

    The mouse cursor is then overridden with Qt::WaitCursor before we fill
    a QStringList object, \c words, with the contents of \c file. Once this
    is done, we restore the mouse cursor.

    \snippet tools/completer/mainwindow.cpp 6

    As mentioned earlier, the resources file contains two files -
    \e{countries.txt} and \e{words.txt}. If the \c file read is \e{words.txt},
    we return a QStringListModel with \c words as its QStringList and
    \c completer as its parent.

    \snippet tools/completer/mainwindow.cpp 7

    If the \c file read is \e{countries.txt}, then we require a
    QStandardItemModel with \c words.count() rows, 2 columns, and \c completer
    as its parent.

    \snippet tools/completer/mainwindow.cpp 8

    A standard line in \e{countries.txt} is:
    \quotation
        Norway                          NO
    \endquotation

    Hence, to populate the QStandardItemModel object, \c m, we have to
    split the country name and its symbol. Once this is done, we return
    \c m.

    \snippet tools/completer/mainwindow.cpp 9

    The \c changeMode() function sets the \c{completer}'s mode, depending on
    the value of \c index.

    \snippet tools/completer/mainwindow.cpp 10

    The \c changeModel() function changes the item model used based on the
    model selected by the user.

    A \c switch statement is used to change the item model based on the index
    of \c modelCombo. If \c case is 0, we use an unsorted QFileSystemModel, providing
    us with a file path excluding the drive label.

    \snippet tools/completer/mainwindow.cpp 11

    Note that we create the model with \c completer as the parent as this
    allows us to replace the model with a new model. The \c completer will
    ensure that the old one is deleted the moment a new model is assigned
    to it.

    If \c case is 1, we use the \c DirModel we defined earlier, resulting in
    full paths for the files.

    \snippet tools/completer/mainwindow.cpp 12

    When \c case is 2, we attempt to complete names of countries. This requires
    a QTreeView object, \c treeView. The country names are extracted from
    \e{countries.txt} and set the popup used to display completions to
    \c treeView.

    \snippet tools/completer/mainwindow.cpp 13

    The screenshot below shows the Completer with the country list model.

    \image completer-example-country.png

    If \c case is 3, we attempt to complete words. This is done using a
    QStringListModel that contains data extracted from \e{words.txt}. The
    model is sorted \l{QCompleter::CaseInsensitivelySortedModel}
    {case insensitively}.

    The screenshot below shows the Completer with the word list model.

    \image completer-example-word.png

    Once the model type is selected, we call the \c changeMode() function and
    the \c changeCase() function and set the wrap option accordingly. The
    \c{wrapCheckBox}'s \l{QCheckBox::clicked()}{clicked()} signal is connected
    to the \c{completer}'s \l{QCompleter::setWrapAround()}{setWrapAround()}
    slot.

    \snippet tools/completer/mainwindow.cpp 14

    The \c changeMaxVisible() updates the maximum number of visible items in
    the completer.

    \snippet tools/completer/mainwindow.cpp 15

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

    \snippet tools/completer/mainwindow.cpp 16

    \section1 \c main() Function

    The \c main() function instantiates QApplication and \c MainWindow and
    invokes the \l{QWidget::show()}{show()} function.

    \snippet tools/completer/main.cpp 0
    */