Qt 5.6 alpha QtWebEngine.如何使用QWebEngineUrlRequestJob

Qt 5.6 alpha QtWebEngine. How work with QWebEngineUrlRequestJob?

本文关键字：何使用 QWebEngineUrlRequestJob QtWebEngine alpha Qt      更新时间：2023-10-16

我继承了QWebEngineUrlSchemeHandler。重新定义的方法请求已启动（QWebEngineUrlRequestJob*请求）

在我尝试调用QWebEngineUrlRequestJob:：回复之后

例如

void CustomUrlSchemeHandler::requestStarted(QWebEngineUrlRequestJob *request)
{
    qDebug() << "CustomUrlSchemeHandler::requestStarted -->>> " << request->requestUrl();
    QMimeDatabase HelpViewer;
    QMimeType mt = HelpViewer.mimeTypeForUrl(request->requestUrl());
    const QString mimeType = mt.name();
    QByteArray arr = QString::fromStdString("<html><body>Hello world</body></html>").toUtf8();
    QBuffer *buffer = new QBuffer(&arr, this);
    buffer->open(QIODevice::ReadOnly);
    request->reply(mimeType.toLatin1(), buffer);
    return;
}

但是程序崩溃了。参见日志：

    [1126/113403:FATAL:weak_ptr.cc(26)] Check failed: sequence_checker_.CalledOnValidSequencedThread(). WeakPtrs must be checked on the same sequenced thread.
Backtrace:
    base::debug::StackTrace::StackTrace [0x11A78691+33] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumbasedebugstack_trace_win.cc:205)
    logging::LogMessage::~LogMessage [0x119CB2AF+63] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumbaselogging.cc:544)
    base::internal::WeakReference::Flag::IsValid [0x119FB75A+234] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumbasememoryweak_ptr.cc:28)
    base::internal::WeakReference::is_valid [0x119FB7B2+50] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumbasememoryweak_ptr.cc:43)
    base::WeakPtr<base::ObserverListBase<content::ServiceWorkerContextObserver> >::get [0x109EF57F+31] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumbasememoryweak_ptr.h:204)
    base::internal::InvokeHelper<1,void,base::internal::RunnableAdapter<void (__thiscall content::DownloadResourceHandler::*)(void)>,base::internal::TypeList<base::WeakPtr<content::DownloadResourceHandler> const &> >::MakeItSo [0x107B8ADB+11] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumbasebind_internal.h:300)
    base::internal::Invoker<base::IndexSequence<0>,base::internal::BindState<base::internal::RunnableAdapter<void (__thiscall content::DownloadResourceHandler::*)(void)>,void __cdecl(content::DownloadResourceHandler *),base::internal::TypeList<base::WeakPtr<c [0x107BAD0A+58] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumbasebind_internal.h:346)
    base::Callback<net::URLRequestContext * __cdecl(void)>::Run [0x1096CACF+47] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumbasecallback.h:396)
    base::debug::TaskAnnotator::RunTask [0x11A9580D+541] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumbasedebugtask_annotator.cc:64)
    base::MessageLoop::RunTask [0x119DAAF8+456] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumbasemessage_loopmessage_loop.cc:475)
    base::MessageLoop::DeferOrRunPendingTask [0x119D9204+52] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumbasemessage_loopmessage_loop.cc:485)
    base::MessageLoop::DoWork [0x119D974D+221] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumbasemessage_loopmessage_loop.cc:594)
    base::MessagePumpForIO::DoRunLoop [0x11A980A2+50] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumbasemessage_loopmessage_pump_win.cc:524)
    base::MessagePumpWin::RunWithDispatcher [0x11A99B42+130] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumbasemessage_loopmessage_pump_win.cc:51)
    base::MessagePumpWin::Run [0x11A99AAC+28] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumbasemessage_loopmessage_pump_win.cc:58)
    base::MessageLoop::RunHandler [0x119DA907+247] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumbasemessage_loopmessage_loop.cc:438)
    base::RunLoop::Run [0x11A0A2E6+70] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumbaserun_loop.cc:56)
    base::MessageLoop::Run [0x119DA7BD+237] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumbasemessage_loopmessage_loop.cc:288)
    base::Thread::Run [0x11A20AF6+22] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumbasethreadingthread.cc:199)
    content::BrowserThreadImpl::IOThreadRun [0x10603B74+52] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumcontentbrowserbrowser_thread_impl.cc:212)
    content::BrowserThreadImpl::Run [0x1060498B+235] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumcontentbrowserbrowser_thread_impl.cc:246)
    base::Thread::ThreadMain [0x11A215F9+745] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumbasethreadingthread.cc:248)
    base::`anonymous namespace'::ThreadFunc [0x11A283B6+262] (e:libqtqt_gitqt5qtwebenginesrc3rdpartychromiumbasethreadingplatform_thread_win.cc:84)
    BaseThreadInitThunk [0x75D57C04+36]
    RtlInitializeExceptionChain [0x77E4AD1F+143]
    RtlInitializeExceptionChain [0x77E4ACEA+90]
    (No symbol) [0x00000000]

崩溃的原因并不明显，因为Qt文档不清楚QWebEngineUrlSchemeHandler应该如何实现的细节。

您的程序崩溃，因为QWebEngineUrlRequestJob::reply()稍后在调用程序的作用域之外使用buffer参数，可能来自其他线程。到那时，您在堆栈上声明的局部变量QByteArrayarr（用作缓冲区的后备存储）将超出范围，QWebEngine将访问无效指针。

另一件事是，reply()不拥有传递的buffer对象的所有权，也从不删除它。这会导致内存泄漏。由于与上述相同的原因，您不能在调用reply()后立即删除它。为确保不再需要缓冲区对象时删除，请将请求的destroyed()信号连接到缓冲器中的deleteLater()插槽。

这是一个完整的工作和无泄漏的例子：

void CustomUrlSchemeHandler::requestStarted(QWebEngineUrlRequestJob *request)
{
    QBuffer *buffer = new QBuffer;
    connect(request, SIGNAL(destroyed()), buffer, SLOT(deleteLater()));
    buffer->open(QIODevice::WriteOnly);
    buffer->write("<html><body>Hello world!</body></html>");
    buffer->close();
    request->reply("text/html", buffer);
}

注意：您根本不需要使用QByteArray。QBuffer的默认构造函数分配自己的存储。

崩溃的一个原因是arr超出了范围。
你必须更改

QByteArray arr = QString::fromStdString("<html><body>Hello world</body></html>").toUtf8();
QBuffer *buffer = new QBuffer(&arr, this);

至

QByteArray *pArr = new QByteArray(QString::fromStdString("<html><body>Hello world</body></html>").toUtf8());
QBuffer *buffer = new QBuffer(pArr, this);
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