Why is QWebEngineView::loadFinished triggered only once?

odelaune

Here is the code

CMakeLists.txt

cmake_minimum_required(VERSION 3.5)

project(test_QWebEngineView_loading LANGUAGES CXX)

set(CMAKE_INCLUDE_CURRENT_DIR ON)

set(CMAKE_AUTOUIC ON)
set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTORCC ON)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(Qt5 COMPONENTS REQUIRED Core Widgets WebEngineWidgets)

set(SOURCE_FILES
  main.cpp
  test.cpp)

add_executable(test_QWebEngineView_loading ${SOURCE_FILES})

target_link_libraries(test_QWebEngineView_loading PRIVATE
  Qt5::Core
  Qt5::Widgets
  Qt5::WebEngineWidgets)

main.cpp

#include <QApplication>

#include "test.h"

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    Test w;
    w.resize(800,600);
    w.show();
    return app.exec();
}

test.h

#ifndef TEST_H
#define TEST_H

#include <QMainWindow>
#include <QWebEngineView>

class Test : public QMainWindow
{
  Q_OBJECT
public:
  explicit Test(QWidget* parent = nullptr);
  ~Test() override;

public slots:

private:
  QWebEngineView *m_website;

  QString m_url;
};

#endif // TEST_H

test.cpp

// Qt headers
#include <QUrl>
#include <QTimer>

// Other headers
#include "test.h"

Test::Test(QWidget* parent /*=nullptr*/):
  QMainWindow(parent)
{;
  m_website = new QWebEngineView();
  setCentralWidget(m_website);
  
  /////////////////////////////////////
  QObject::connect(m_website, &QWebEngineView::loadFinished, [this](bool isOk) {
    if (!isOk) {
      qDebug() << "Error when loading URL";
      return;
    }
    qDebug() << "Loading " << m_url << "is finished";

  });
  
  // one loads a first URL
  // Paris
  m_url = QString("https://www.openstreetmap.org/#map=11/48.8578/2.4093");
  qDebug() << "loading " << m_url << "...";
  m_website->load(QUrl(m_url));


  // waiting 2 seconds and then loading a new URL
  QTimer::singleShot(2000, [this](){ // 2 sec.
    // Ha Noi 21.0102/105.8134
    m_url = QString("https://www.openstreetmap.org/#map=11/21.0102/105.8134");
    qDebug() << "loading " << m_url << "...";
    m_website->load(QUrl(m_url));
  });
}

// destructor
Test::~Test()
{
  delete m_website;
}

Here is the output:

loading "https://www.openstreetmap.org/#map=11/48.8578/2.4093" ...
Loading "https://www.openstreetmap.org/#map=11/48.8578/2.4093" is finished
loading "https://www.openstreetmap.org/#map=11/21.0102/105.8134" ...

I am wondering why the signal &QWebEngineView::loadFinished is not emitted when I load the second URL while the page is well displayed in the QMainWindow. Why do I not see the line "Loading "https://www.openstreetmap.org/#map=11/21.0102/105.8134 is finished"?

kkoehne

Which Qt version / Qt WebEngine version are you testing with?

THere were a couple of fixes related to loadFinished() in Qt 5.15, namely https://codereview.qt-project.org/c/qt/qtwebengine/+/340965

odelaune

I use Qt 5.15.3 from Ubuntu 22.04 packages. I guess this is the same version for QtWebEngine.

JonB

@odelaune
Not an answer to how many times loadFinished is called, but be careful if you use code like this for real. Your m_url is altered after 2 seconds, your first loadFinished should not assume that it is still its original url by the time the slot is called....