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166 lines
6.3 KiB
Plaintext
166 lines
6.3 KiB
Plaintext
// Copyright (C) 2016 The Qt Company Ltd.
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// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
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/*!
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\example tools/customcompleter
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\title Custom Completer Example
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\ingroup examples-widgets-tools
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\brief The Custom Completer example shows how to provide string-completion
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facilities for an input widget based on data provided by a model. The
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completer pops up suggestions for possible words based on the first three
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characters input by the user and the user's choice of word is inserted
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into the \c TextEdit using QTextCursor.
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\image customcompleter-example.png
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\section1 Setting Up The Resource File
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The Custom Completer example requires a resource file, \e wordlist.txt,
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that has a list of words to help QCompleter complete words. This file
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contains the following:
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\quotefile tools/customcompleter/customcompleter.qrc
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\section1 TextEdit Class Definition
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The \c TextEdit class is a subclass of QTextEdit with a custom
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\c insertCompletion() slot and it reimplements the
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\l{QAbstractScrollArea::keyPressEvent()}{keyPressEvent()} and the
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\l{QWidget::focusInEvent()}{focusInEvent()} functions. \c TextEdit also
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contains a private function \c textUnderCursor() and a private instance
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of QCompleter, \c c.
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\snippet tools/customcompleter/textedit.h 0
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\section1 TextEdit Class Implementation
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The constructor for \c TextEdit constructs a \c TextEdit with a parent and
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initializes \c c. The instructions to use the completer is displayed on
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the \c TextEdit object, using the
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\l{QTextEdit::setPlainText()}{setPlainText()} function.
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\snippet tools/customcompleter/textedit.cpp 0
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In addition, \c TextEdit also includes a default destructor:
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\snippet tools/customcompleter/textedit.cpp 1
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The \c setCompleter() function accepts a \a completer and sets it up.
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We use \c{if (c)} to check if \c c has been initialized. If it has been
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initialized, the QObject::disconnect() function is invoked to disconnect
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the signal from the slot. This is to ensure that no previous completer
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object is still connected to the slot.
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\snippet tools/customcompleter/textedit.cpp 2
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We then instantiate \c c with \a completer and set it as \c{TextEdit}'s
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widget. The completion mode and case sensitivity are also set and then
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we connect the \l{QCompleter::activated()}{activated()} signal to the
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\c insertCompletion() slot.
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The \c completer() function is a getter function that returns \c c.
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\snippet tools/customcompleter/textedit.cpp 3
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The completer pops up the options available, based on the contents of
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\e wordlist.txt, but the text cursor is responsible for filling in the
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missing characters, according to the user's choice of word.
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Suppose the user inputs "ACT" and accepts the completer's suggestion of
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"ACTUAL". The \c completion string is then sent to \c insertCompletion()
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by the completer's \l{QCompleter::activated()}{activated()} signal.
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The \c insertCompletion() function is responsible for completing the word
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using a QTextCursor object, \c tc. It validates to ensure that the
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completer's widget is \c TextEdit before using \c tc to insert the extra
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characters to complete the word.
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\snippet tools/customcompleter/textedit.cpp 4
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The figure below illustrates this process:
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\image customcompleter-insertcompletion.png
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\c{completion.length()} = 6
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\c{c->completionPrefix().length()}=3
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The difference between these two values is \c extra, which is 3. This
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means that the last three characters from the right, "U", "A", and "L",
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will be inserted by \c tc.
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The \c textUnderCursor() function uses a QTextCursor, \c tc, to select a
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word under the cursor and return it.
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\snippet tools/customcompleter/textedit.cpp 5
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The \c TextEdit class reimplements \l{QWidget::focusInEvent()}
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{focusInEvent()} function, which is an event handler used to receive
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keyboard focus events for the widget.
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\snippet tools/customcompleter/textedit.cpp 6
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The \l{QAbstractScrollArea::keyPressEvent()}{keyPressEvent()} is
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reimplemented to ignore key events like Qt::Key_Enter, Qt::Key_Return,
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Qt::Key_Escape, Qt::Key_Tab, and Qt::Key_Backtab so the completer can
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handle them.
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If there is an active completer, we cannot process the shortcut, Ctrl+E.
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\snippet tools/customcompleter/textedit.cpp 7
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We also handle other modifiers and shortcuts for which we do not want the
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completer to respond to.
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\snippet tools/customcompleter/textedit.cpp 8
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Finally, we pop up the completer.
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\section1 MainWindow Class Definition
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The \c MainWindow class is a subclass of QMainWindow and implements a
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private slot, \c about(). This class also has two private functions,
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\c createMenu() and \c modelFromFile() as well as private instances of
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QCompleter and \c TextEdit.
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\snippet tools/customcompleter/mainwindow.h 0
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\section1 MainWindow Class Implementation
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The constructor constructs a \c MainWindow with a parent and initializes
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the \c completer. It also instantiates a \c TextEdit and sets its
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completer. A QStringListModel, obtained from \c modelFromFile(), is used
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to populate the \c completer. The \c{MainWindow}'s central widget is set
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to \c TextEdit and its size is set to 500 x 300.
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\snippet tools/customcompleter/mainwindow.cpp 0
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The \c createMenu() function creates the necessary QAction objects needed
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for the "File" and "Help" menu and their \l{QAction::triggered()}
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{triggered()} signals are connected to the \c quit(), \c about(), and
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\c aboutQt() slots respectively.
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\snippet tools/customcompleter/mainwindow.cpp 1
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The \c modelFromFile() function accepts a \a fileName and attempts to
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extract the contents of this file into a QStringListModel. We display the
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Qt::WaitCursor when we are populating the QStringList, \c words, and
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restore the mouse cursor when we are done.
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\snippet tools/customcompleter/mainwindow.cpp 2
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The \c about() function provides a brief description about the Custom
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Completer example.
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\snippet tools/customcompleter/mainwindow.cpp 3
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\section1 \c main() Function
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The \c main() function instantiates \c MainWindow and invokes the
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\l{QWidget::show()}{show()} function.
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\snippet tools/customcompleter/main.cpp 0
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*/
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