QT分析之WebKit（三）
分三个阶段对QWebView进行分析：初始化（获取数据）、HTML解析、页面显示。从QT自带的文档中可以知道：
QWebView -> QWebPage => QWebFrame（一个QWebPage含多个QWebFrame）
在界面中选择了Open URL，输入URL之后，调用的是：void MainWindow::openUrl()
void MainWindow::openUrl()
{
bool ok;
QString url = QInputDialog::getText(this, tr("Enter a URL"),
tr("URL:"), QLineEdit::Normal, "http://", &ok);
if (ok && !url.isEmpty()) {
centralWidget->webView->setUrl(url);
}
}
调用的是QWebView::setUrl()
void QWebView::setUrl(const QUrl &url)
{
page()->mainFrame()->setUrl(url);
}
其中page()是获取QWebPage指针，QWebPage::mainFrame()获取的是QWebFrame指针。
所以调用的是：QWebFrame::setUrl()
void QWebFrame::setUrl(const QUrl &url)
{
d->frame->loader()->begin(ensureAbsoluteUrl(url));
d->frame->loader()->end();
load(ensureAbsoluteUrl(url));
}
ensureAbsoluteUrl()函数作用是，确保URL是绝对URL（完整URL）。所谓相对URL是指没有输入http://或者https://等前缀的web地址。先看第一句的调用。其中隐含了从QUrl到KURL的变换。
void FrameLoader::begin(const KURL& url, bool dispatch, SecurityOrigin* origin)
{
// We need to take a reference to the security origin because |clear|
// might destroy the document that owns it.
RefPtr<SecurityOrigin> forcedSecurityOrigin = origin;
bool resetScripting = !(m_isDisplayingInitialEmptyDocument && m_frame->document() && m_frame->document()->securityOrigin()->isSecureTransitionTo(url));
clear(resetScripting, resetScripting); // 清除上一次的数据，为本次装载准备
if (resetScripting)
m_frame->script()->updatePlatformScriptObjects(); // 在Windows平台下，这是空函数
if (dispatch)
dispatchWindowObjectAvailable();
m_needsClear = true;
m_isComplete = false;
m_didCallImplicitClose = false;
m_isLoadingMainResource = true;
m_isDisplayingInitialEmptyDocument = m_creatingInitialEmptyDocument;
KURL ref(url);
ref.setUser(String());
ref.setPass(String());
ref.setRef(String());
m_outgoingReferrer = ref.string();
m_URL = url;
RefPtr<Document> document;
if (!m_isDisplayingInitialEmptyDocument && m_client->shouldUsePluginDocument(m_responseMIMEType))
document = PluginDocument::create(m_frame);
else
document = DOMImplementation::createDocument(m_responseMIMEType, m_frame, m_frame->inViewSourceMode()); // 创建DOM文件，m_responseMIMEType不同实体不同。
// 如果是"text/html"创建HTMLDocument实体；"application/xhtml+xml"创建Document实体
// 如果是"application/x-ftp-directory"则是FTPDirectoryDocument实体
// text/vnd.wap.wml 对应 WMLDocument 实体（无线）
// "application/pdf" /"text/plain" 对应 PluginDocument实体
// 如果是MediaPlayer::supportsType(type)，创建的是MediaDocument实体
// "image/svg+xml" 对应 SVGDocument实体
m_frame->setDocument(document);
document->setURL(m_URL);
if (m_decoder)
document->setDecoder(m_decoder.get());
if (forcedSecurityOrigin)
document->setSecurityOrigin(forcedSecurityOrigin.get());
m_frame->domWindow()->setURL(document->url());
m_frame->domWindow()->setSecurityOrigin(document->securityOrigin());
updatePolicyBaseURL(); // 更新排布策略的基础URL
Settings* settings = document->settings();
document->docLoader()->setAutoLoadImages(settings && settings->loadsImagesAutomatically());
if (m_documentLoader) {
String dnsPrefetchControl = m_documentLoader->response().httpHeaderField("X-DNS-Prefetch-Control");
if (!dnsPrefetchControl.isEmpty())
document->parseDNSPrefetchControlHeader(dnsPrefetchControl);
}
#if FRAME_LOADS_USER_STYLESHEET
KURL userStyleSheet = settings ? settings->userStyleSheetLocation() : KURL();
if (!userStyleSheet.isEmpty())
m_frame->setUserStyleSheetLocation(userStyleSheet);
#endif
restoreDocumentState();
document->implicitOpen();
if (m_frame->view())
m_frame->view()->setContentsSize(IntSize());
#if USE(LOW_BANDWIDTH_DISPLAY)
// Low bandwidth display is a first pass display without external resources
// used to give an instant visual feedback. We currently only enable it for
// HTML documents in the top frame.
if (document->isHTMLDocument() && !m_frame->tree()->parent() && m_useLowBandwidthDisplay) {
m_pendingSourceInLowBandwidthDisplay = String();
m_finishedParsingDuringLowBandwidthDisplay = false;
m_needToSwitchOutLowBandwidthDisplay = false;
document->setLowBandwidthDisplay(true);
}
#endif
}
看其中document->implicitOpen()的代码：
void Document::implicitOpen()
{
cancelParsing();
clear();
m_tokenizer = createTokenizer();
setParsing(true);
}
Tokenizer *HTMLDocument::createTokenizer()
{
bool reportErrors = false;
if (frame())
if (Page* page = frame()->page())
reportErrors = page->inspectorController()->windowVisible();
return new HTMLTokenizer(this, reportErrors);
}
新创建的HTMLTokenizer对象，就是HTML的解析器。
回到QWebFrame::setUrl()的第二句：d->frame->loader()->end();
只是把上次未完的解析停止：
void FrameLoader::endIfNotLoadingMainResource()
{
if (m_isLoadingMainResource || !m_frame->page())
return;
// http://bugs.webkit.org/show_bug.cgi?id=10854
// The frame's last ref may be removed and it can be deleted by checkCompleted(),
// so we'll add a protective refcount
RefPtr<Frame> protector(m_frame);
// make sure nothing's left in there
if (m_frame->document()) {
write(0, 0, true);
m_frame->document()->finishParsing();
} else
// WebKit partially uses WebCore when loading non-HTML docs. In these cases doc==nil, but
// WebCore is enough involved that we need to checkCompleted() in order for m_bComplete to
// become true. An example is when a subframe is a pure text doc, and that subframe is the
// last one to complete.
checkCompleted();
}
再来看QWebFrame::setUrl()的第三句：load(ensureAbsoluteUrl(url));
void QWebFrame::load(const QUrl &url)
{
load(QNetworkRequest(ensureAbsoluteUrl(url)));
}
新建一个QNetworkRequest对象，然后调用
void load(const QNetworkRequest &request,
QNetworkAccessManager::Operation operation = QNetworkAccessManager::GetOperation,
const QByteArray &body = QByteArray());
看其代码：
void QWebFrame::load(const QNetworkRequest &req,
QNetworkAccessManager::Operation operation,
const QByteArray &body)
{
if (d->parentFrame())
d->page->d->insideOpenCall = true;
QUrl url = ensureAbsoluteUrl(req.url());
WebCore::ResourceRequest request(url);
switch (operation) {
case QNetworkAccessManager::HeadOperation:
request.setHTTPMethod("HEAD");
break;
case QNetworkAccessManager::GetOperation:
request.setHTTPMethod("GET");
break;
case QNetworkAccessManager::PutOperation:
request.setHTTPMethod("PUT");
break;
case QNetworkAccessManager::PostOperation:
request.setHTTPMethod("POST");
break;
case QNetworkAccessManager::UnknownOperation:
// eh?
break;
}
QList<QByteArray> httpHeaders = req.rawHeaderList();
for (int i = 0; i < httpHeaders.size(); ++i) {
const QByteArray &headerName = httpHeaders.at(i);
request.addHTTPHeaderField(QString::fromLatin1(headerName), QString::fromLatin1(req.rawHeader(headerName)));
}
if (!body.isEmpty())
request.setHTTPBody(WebCore::FormData::create(body.constData(), body.size()));
d->frame->loader()->load(request);
if (d->parentFrame())
d->page->d->insideOpenCall = false;
}
看关键的FrameLoader::load()
void FrameLoader::load(const ResourceRequest& request)
{
load(request, SubstituteData());
}
void FrameLoader::load(const ResourceRequest& request, const SubstituteData& substituteData)
{
if (m_inStopAllLoaders)
return;
// FIXME: is this the right place to reset loadType? Perhaps this should be done after loading is finished or aborted.
m_loadType = FrameLoadTypeStandard;
load(m_client->createDocumentLoader(request, substituteData).get());
}
上面m_client对应的是FrameLoaderClientQt实体，m_client->createDocumentLoader()创建的是DocumentLoader对象。进一步看FrameLoader::load(DocumentLoader *)的代码：
void FrameLoader::load(DocumentLoader* newDocumentLoader)
{
ResourceRequest& r = newDocumentLoader->request();
addExtraFieldsToMainResourceRequest(r);
FrameLoadType type;
if (shouldTreatURLAsSameAsCurrent(newDocumentLoader->originalRequest().url())) {
r.setCachePolicy(ReloadIgnoringCacheData);
type = FrameLoadTypeSame;
} else
type = FrameLoadTypeStandard;
if (m_documentLoader)
newDocumentLoader->setOverrideEncoding(m_documentLoader->overrideEncoding());
// When we loading alternate content for an unreachable URL that we're
// visiting in the history list, we treat it as a reload so the history list
// is appropriately maintained.
//
// FIXME: This seems like a dangerous overloading of the meaning of "FrameLoadTypeReload" ...
// shouldn't a more explicit type of reload be defined, that means roughly
// "load without affecting history" ?
if (shouldReloadToHandleUnreachableURL(newDocumentLoader)) {
ASSERT(type == FrameLoadTypeStandard);
type = FrameLoadTypeReload;
}
loadWithDocumentLoader(newDocumentLoader, type, 0);
}