Sharma, Ashish wrote:
Hello,
I am using Qt webkit Jambi API's to convert HTML to PDF.
My target is to create a jar for above conversion so that it could be
used in a multithreading environment, but since QWebPage and QWebframe
(QT webkit) are GUI classes, therefore the jar classes cannot be
initialized from child threads.
It's true that certain actions are restricted to the gui thread (such as
using widgets), but painting to a printer is allowed, as described here:
http://doc.trolltech.com/qtjambi-4.5.0_01/com/trolltech/qt/qtjambi-threads.html#painting-in-threads
A restriction on QWebPage is that it has to be constructed in the GUI
thread, since it accesses QApplication. However, you can use
QObject.moveToThread() to move QObjects over to a different thread than
the one that created it.
See the attached example of how to make a thread-based web page renderer
that renders into a .pdf. (it's a quick&dirty example, so please excuse
any bugs, but it should at least illustrate how to achieve what you need.)
The example makes a widget which monitors the progress of loading the
web page. The QWebPage is constructed in the gui thread, and made a
child of the runnable object. Then the entire hierarchy is moved to the
thread in question. The run() method in the runnable starts loading the
web page, and when it completes, the web page is rendered into a
.pdf-printer and the application is shut down.
Also i am a novice in QT , can anyone provide good reference about QT
application's lifecycle, event loops and related stuff.
Threads and event loops are described here:
http://doc.trolltech.com/qtjambi-4.5.0_01/com/trolltech/qt/qtjambi-threads.html
And here are a few whitepapers which may contain more information:
https://www.qtsoftware.com/files/pdf
-- Eskil
package com.trolltech.test;
import com.trolltech.qt.*;
import com.trolltech.qt.core.*;
import com.trolltech.qt.gui.*;
import com.trolltech.qt.webkit.*;
public class WebFrameInThread extends QLabel {
public WebFrameInThread() {
MyRunnable runnable = new MyRunnable();
QThread thread = new QThread(runnable);
runnable.moveToThread(thread);
thread.start();
}
private class MyRunnable extends QObject implements Runnable {
private QWebPage page;
private QEventLoop loop;
public MyRunnable() {
page = new QWebPage(this);
}
public void run() {
try {
page.loadFinished.connect(this, "loadFinished()");
page.loadProgress.connect(this, "loadProgress(int)");
page.mainFrame().load(new QUrl("http://www.qtsoftware.com";));
} catch (Throwable e) {
e.printStackTrace();
}
loop = new QEventLoop();
loop.exec();
}
public void loadProgress(final int progress) {
QApplication.invokeLater(new Runnable() {
public void run() {
setText(progress + "%");
}
});
}
public void loadFinished() {
page.setViewportSize(page.mainFrame().contentsSize());
QPrinter printer = new QPrinter();
printer.setOutputFileName("output.pdf");
printer.setOutputFormat(QPrinter.OutputFormat.PdfFormat);
QPainter painter = new QPainter();
painter.begin(printer);
page.mainFrame().render(painter);
painter.end();
loop.exit();
QApplication.invokeLater(new Runnable() {
public void run() {
close();
}
});
}
}
public static void main(String args[]) {
QApplication.initialize(args);
QWidget widget = new WebFrameInThread();
widget.show();
QApplication.exec();
}
}
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