演示如何打印网页使用 Qt WebEngine Widgets.
PrintMe 演示如何使用 QWebEnginePage and QPrintDialog classes to print a web page. Further, it shows how to implement print preview by using the QPrintPreviewDialog class. For completeness, it also illustrates how to trigger a printing request within JavaScript.
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In this example, we create an internal HTML page that is added as a resource collection file (.qrc). The page shows only a small HTML message box that explains how to trigger printing by using keyboard shortcuts or clicking a button. The button has the JavaScript
onclick
event attribute that calls the JavaScript
window.print()
函数。
<html lang="en"> <head> <meta charset="utf-8"> <title>PrintMe</title> <link rel="stylesheet" type="text/css" href="style.css"> <script> function printNow() { window.print(); } </script> </head> <body> <form class="form"> <img class="logo" src="icon.svg" alt="qtwebengine"> <div class="header"> <h1>Hello Paper World!</h1> <h2>Press Ctrl+p to print with print preview</h2> <h2>Press Ctrl+Shift+p to print without print preview</h2> <h2>Click the button to print using JavaScript</h2> <p class="button" onclick="printNow()">Print Now</p> </form> </body> </html>
在
main
function, we first instantiate a
QWebEngineView
and set the URL to our internal HTML page. Next, we create a
PrintHandler
instance and pass the requested page. For convenience, we also create keyboard shortcuts that can be used to call a print dialog or print preview dialog.
QWebEngineView view; view.setUrl(QUrl(QStringLiteral("qrc:/index.html"))); view.resize(1024, 750); view.show(); PrintHandler handler; handler.setPage(view.page()); auto printPreviewShortCut = new QShortcut(QKeySequence(Qt::CTRL + Qt::Key_P), &view); auto printShortCut = new QShortcut(QKeySequence(Qt::CTRL + Qt::SHIFT + Qt::Key_P), &view); QObject::connect(printPreviewShortCut, &QShortcut::activated, &handler, &PrintHandler::printPreview); QObject::connect(printShortCut, &QShortcut::activated, &handler, &PrintHandler::print);
在
PrintHandler
function, we first implement
printPreview()
, where we instantiate
QPrinter
together with
QPrintPreviewDialog
. We need the
QPrintPreviewDialog::paintRequested
handle to generate a set of preview pages.
void PrintHandler::printPreview() { if (!m_page) return; if (m_inPrintPreview) return; m_inPrintPreview = true; QPrinter printer; printer.setResolution(300); QPrintPreviewDialog preview(&printer, m_page->view()); connect(&preview, &QPrintPreviewDialog::paintRequested, this, &PrintHandler::printDocument); preview.exec(); m_inPrintPreview = false; }
Now we can implement the
PrintHandler::printDocument()
slot, which is called in response to the
QPrintPreviewDialog::paintRequested
信号。
void PrintHandler::printDocument(QPrinter *printer) { QEventLoop loop; bool result; auto printPreview = [&](bool success) { result = success; loop.quit(); }; m_page->print(printer, std::move(printPreview)); loop.exec(); if (!result) { QPainter painter; if (painter.begin(printer)) { QFont font = painter.font(); font.setPixelSize(20); painter.setFont(font); painter.drawText(QPointF(10,25), QStringLiteral("Could not generate print preview.")); painter.end(); } } }
To do actual painting on a printer, we call the
QWebEnginePage::print
() function. Because this call blocks the main event loop, we need to create a local one. We begin the local event loop by calling
QEventLoop::exec
(). When the local event loop terminates, we check for
result
and report any errors that occurred.
The last function we implement,
PrintHandler::print()
, is trivial, because it simply opens
QPrintDialog
and calls the previously implemented
PrintHandler::printDocument()
.
void PrintHandler::print() { QPrinter printer(QPrinter::HighResolution); QPrintDialog dialog(&printer, m_page->view()); if (dialog.exec() != QDialog::Accepted) return; printDocument(&printer); }