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
TextEdit
使用
QTextCursor
.
The Custom Completer example requires a resource file, wordlist.txt , that has a list of words to help QCompleter complete words. This file contains the following:
<!DOCTYPE RCC><RCC version="1.0"> <qresource prefix="/"> <file>resources/wordlist.txt</file> </qresource> </RCC>
The
TextEdit
类是子类化的
QTextEdit
with a custom
insertCompletion()
slot and it reimplements the
keyPressEvent
() 和
focusInEvent
() 函数。
TextEdit
also contains a private function
textUnderCursor()
and a private instance of
QCompleter
,
c
.
class TextEdit : public QTextEdit { Q_OBJECT public: TextEdit(QWidget *parent = nullptr); ~TextEdit(); void setCompleter(QCompleter *c); QCompleter *completer() const; protected: void keyPressEvent(QKeyEvent *e) override; void focusInEvent(QFocusEvent *e) override; private slots: void insertCompletion(const QString &completion); private: QString textUnderCursor() const; private: QCompleter *c = nullptr; };
The constructor for
TextEdit
constructs a
TextEdit
with a parent and initializes
c
. The instructions to use the completer is displayed on the
TextEdit
object, using the
setPlainText
() 函数。
TextEdit::TextEdit(QWidget *parent) : QTextEdit(parent) { setPlainText(tr("This TextEdit provides autocompletions for words that have more than" " 3 characters. You can trigger autocompletion using ") + QKeySequence("Ctrl+E").toString(QKeySequence::NativeText)); }
此外，
TextEdit
also includes a default destructor:
TextEdit::~TextEdit() { }
The
setCompleter()
function accepts a
completer
and sets it up. We use
if (c)
to check if
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.
void TextEdit::setCompleter(QCompleter *completer) { if (c) c->disconnect(this); c = completer; if (!c) return; c->setWidget(this); c->setCompletionMode(QCompleter::PopupCompletion); c->setCaseSensitivity(Qt::CaseInsensitive); QObject::connect(c, QOverload<const QString &>::of(&QCompleter::activated), this, &TextEdit::insertCompletion); }
We then instantiate
c
with
completer
and set it as
TextEdit
's widget. The completion mode and case sensitivity are also set and then we connect the
activated
() 信号到
insertCompletion()
槽。
The
completer()
function is a getter function that returns
c
.
QCompleter *TextEdit::completer() const { return c; }
The completer pops up the options available, based on the contents of 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
completion
string is then sent to
insertCompletion()
by the completer's
activated
() 信号。
The
insertCompletion()
function is responsible for completing the word using a
QTextCursor
对象，
tc
. It validates to ensure that the completer's widget is
TextEdit
before using
tc
to insert the extra characters to complete the word.
void TextEdit::insertCompletion(const QString &completion) { if (c->widget() != this) return; QTextCursor tc = textCursor(); int extra = completion.length() - c->completionPrefix().length(); tc.movePosition(QTextCursor::Left); tc.movePosition(QTextCursor::EndOfWord); tc.insertText(completion.right(extra)); setTextCursor(tc); }
The figure below illustrates this process:
completion.length()
= 6
c->completionPrefix().length()
=3
The difference between these two values is
extra
, which is 3. This means that the last three characters from the right, "U", "A", and "L", will be inserted by
tc
.
The
textUnderCursor()
function uses a
QTextCursor
,
tc
, to select a word under the cursor and return it.
QString TextEdit::textUnderCursor() const { QTextCursor tc = textCursor(); tc.select(QTextCursor::WordUnderCursor); return tc.selectedText(); }
The
TextEdit
class reimplements
focusInEvent
() function, which is an event handler used to receive keyboard focus events for the widget.
void TextEdit::focusInEvent(QFocusEvent *e) { if (c) c->setWidget(this); QTextEdit::focusInEvent(e); }
The keyPressEvent () is reimplemented to ignore key events like Qt::Key_Enter , Qt::Key_Return , Qt::Key_Escape , Qt::Key_Tab ，和 Qt::Key_Backtab so the completer can handle them.
If there is an active completer, we cannot process the shortcut, Ctrl+E.
void TextEdit::keyPressEvent(QKeyEvent *e) { if (c && c->popup()->isVisible()) { // The following keys are forwarded by the completer to the widget switch (e->key()) { case Qt::Key_Enter: case Qt::Key_Return: case Qt::Key_Escape: case Qt::Key_Tab: case Qt::Key_Backtab: e->ignore(); return; // let the completer do default behavior default: break; } } const bool isShortcut = (e->modifiers().testFlag(Qt::ControlModifier) && e->key() == Qt::Key_E); // CTRL+E if (!c || !isShortcut) // do not process the shortcut when we have a completer QTextEdit::keyPressEvent(e);
We also handle other modifiers and shortcuts for which we do not want the completer to respond to.
const bool ctrlOrShift = e->modifiers().testFlag(Qt::ControlModifier) ||
e->modifiers().testFlag(Qt::ShiftModifier);
if (!c || (ctrlOrShift && e->text().isEmpty()))
return;
static QString eow("~!@#$%^&*()_+{}|:\"<>?,./;'[]\\-="); // end of word
const bool hasModifier = (e->modifiers() != Qt::NoModifier) && !ctrlOrShift;
QString completionPrefix = textUnderCursor();
if (!isShortcut && (hasModifier || e->text().isEmpty()|| completionPrefix.length() < 3
|| eow.contains(e->text().right(1)))) {
c->popup()->hide();
return;
}
if (completionPrefix != c->completionPrefix()) {
c->setCompletionPrefix(completionPrefix);
c->popup()->setCurrentIndex(c->completionModel()->index(0, 0));
}
QRect cr = cursorRect();
cr.setWidth(c->popup()->sizeHintForColumn(0)
+ c->popup()->verticalScrollBar()->sizeHint().width());
c->complete(cr); // popup it up!
}
Finally, we pop up the completer.
The
MainWindow
类是子类化的
QMainWindow
and implements a private slot,
about()
. This class also has two private functions,
createMenu()
and
modelFromFile()
as well as private instances of
QCompleter
and
TextEdit
.
class MainWindow : public QMainWindow { Q_OBJECT public: MainWindow(QWidget *parent = nullptr); private slots: void about(); private: void createMenu(); QAbstractItemModel *modelFromFile(const QString& fileName); QCompleter *completer = nullptr; TextEdit *completingTextEdit; };
The constructor constructs a
MainWindow
with a parent and initializes the
completer
. It also instantiates a
TextEdit
and sets its completer. A
QStringListModel
, obtained from
modelFromFile()
, is used to populate the
completer
。
MainWindow
's central widget is set to
TextEdit
and its size is set to 500 x 300.
MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent) { createMenu(); completingTextEdit = new TextEdit; completer = new QCompleter(this); completer->setModel(modelFromFile(":/resources/wordlist.txt")); completer->setModelSorting(QCompleter::CaseInsensitivelySortedModel); completer->setCaseSensitivity(Qt::CaseInsensitive); completer->setWrapAround(false); completingTextEdit->setCompleter(completer); setCentralWidget(completingTextEdit); resize(500, 300); setWindowTitle(tr("Completer")); }
The
createMenu()
function creates the necessary
QAction
objects needed for the "File" and "Help" menu and their
triggered
() signals are connected to the
quit()
,
about()
，和
aboutQt()
slots respectively.
void MainWindow::createMenu() { QAction *exitAction = new QAction(tr("Exit"), this); QAction *aboutAct = new QAction(tr("About"), this); QAction *aboutQtAct = new QAction(tr("About Qt"), this); connect(exitAction, &QAction::triggered, qApp, &QApplication::quit); connect(aboutAct, &QAction::triggered, this, &MainWindow::about); connect(aboutQtAct, &QAction::triggered, qApp, &QApplication::aboutQt); QMenu *fileMenu = menuBar()->addMenu(tr("File")); fileMenu->addAction(exitAction); QMenu *helpMenu = menuBar()->addMenu(tr("About")); helpMenu->addAction(aboutAct); helpMenu->addAction(aboutQtAct); }
The
modelFromFile()
function accepts 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
,
words
, and restore the mouse cursor when we are done.
QAbstractItemModel *MainWindow::modelFromFile(const QString& fileName) { QFile file(fileName); if (!file.open(QFile::ReadOnly)) return new QStringListModel(completer); #ifndef QT_NO_CURSOR QGuiApplication::setOverrideCursor(QCursor(Qt::WaitCursor)); #endif QStringList words; while (!file.atEnd()) { QByteArray line = file.readLine(); if (!line.isEmpty()) words << QString::fromUtf8(line.trimmed()); } #ifndef QT_NO_CURSOR QGuiApplication::restoreOverrideCursor(); #endif return new QStringListModel(words, completer); }
The
about()
function provides a brief description about the Custom Completer example.
void MainWindow::about() { QMessageBox::about(this, tr("About"), tr("This example demonstrates the " "different features of the QCompleter class.")); }
main()
函数
The
main()
function instantiates
MainWindow
and invokes the
show
() 函数。
int main(int argc, char *argv[]) { Q_INIT_RESOURCE(customcompleter); QApplication app(argc, argv); MainWindow window; window.show(); return app.exec(); }