谷歌浏览器的源码分析(16)

上一次说到需要调用这个OpenURLFromTab函数，那么这个函数是做什么的呢？从名称上可能猜到它是打开网页，但是是从目前TAB页里打开呢？还是新建一个？或者使用每个TAB页一个进程呢？这些疑惑，只能通过代码的分析来理解它的实现，代码如下：

这个函数的参数意思：
source是TAB内容。
url是网络连接地址。
disposition是窗口打开的位置。
transition是连接传送的类型。
override_encoding是编码类型。

#001 void Browser::OpenURLFromTab(TabContents* source,
#002 const GURL& url,
#003 WindowOpenDisposition disposition,
#004 PageTransition::Type transition,
#005 const std::string& override_encoding) {

调试时检查代码。
#006 // No code for these yet
#007 DCHECK((disposition != NEW_POPUP) && (disposition != S***E_TO_DISK));
#008

获取当前的TAB页。
#009 TabContents* current_tab = source ? source : GetSelectedTabContents();


判断是否当前TAB页选中。
#010 bool source_tab_was_frontmost = (current_tab == GetSelectedTabContents());
#011 TabContents* new_contents = NULL;
#012
#013 // If the URL is part of the same web site, then load it in the same
#014 // SiteInstance (and thus the same process). This is an optimization to
#015 // reduce process overhead; it is not necessary for compatibility. (That is,
#016 // the new tab will not have script connections to the previous tab, so it
#017 // does not need to be part of the same SiteInstance or BrowsingInstance.)
#018 // Default to loading in a new SiteInstance and BrowsingInstance.
#019 // TODO(creis): should this apply to applications?

保存打开连接的实例指针。
#020 SiteInstance* instance = NULL;

如果不使用每个TAB页一个进程的方式，就不需要进行下面的处理。因为同一个连接在一个进程里打开是比较快，这里主要做优化。
#021 // Don't use this logic when "--process-per-tab" is specified.

判断是否有每一个TAB一个进程的方式。
#022 if (!CommandLine().HasSwitch(switches::kProcessPerTab)) {

有当前进程页。
#023 if (current_tab) {
#024 const WebContents* const web_contents = current_tab->AsWebContents();

判断是否相同的网络连接地址。
#025 if (web_contents) {
#026 const GURL& current_url = web_contents->GetURL();

如果相同的网络地址，并且有实例打开，就返回这个实例在instance。
#027 if (SiteInstance::IsSameWebSite(current_url, url))
#028 instance = web_contents->site_instance();
#029 }
#030 }
#031 }
#032
#033 // If this is an application we can only have one tab so a new tab always
#034 // goes into a tabbed browser window.

下面进行不打开新窗口的处理。
#035 if (disposition != NEW_WINDOW && type_ == BrowserType::APPLICATION) {
#036 // If the disposition is OFF_THE_RECORD we don't want to create a new
#037 // browser that will itself create another OTR browser. This will result in
#038 // a browser leak (and crash below because no tab is created or selected).
#039 if (disposition == OFF_THE_RECORD) {
#040 OpenURLOffTheRecord(profile_, url);
#041 return;
#042 }
#043
#044 Browser* b = GetOrCreateTabbedBrowser();
#045 DCHECK(b);
#046
#047 // If we have just created a new browser window, make sure we select the
#048 // tab.
#049 if (b->tab_count() == 0 && disposition == NEW_BACKGROUND_TAB)
#050 disposition = NEW_FOREGROUND_TAB;
#051
#052 b->OpenURL(url, disposition, transition);
#053 b->Show();
#054 b->MoveToFront(true);
#055 return;
#056 }
#057
#058 if (profile_->IsOffTheRecord() && disposition == OFF_THE_RECORD)
#059 disposition = NEW_FOREGROUND_TAB;
#060

这里开始处理打开一个新窗口显示网络连接。
#061 if (disposition == NEW_WINDOW) {

创建一个新的Browser浏览器对象。
#062 Browser* new_browser = new Browser(gfx::Rect(), SW_SHOWNORMAL, profile_,
#063 BrowserType::TABBED_BROWSER, L"");

创建一个TAB内容。
#064 new_contents = new_browser->AddTabWithURL(url, transition, true, instance);

这里开始显示这个网络连接的内容。
#065 new_browser->Show();
#066 } else if ((disposition == CURRENT_TAB) && current_tab) {

下面开始在当前TAB页里打开连接，同时判断处理的类型。
#067 if (transition == PageTransition::TYPED ||
#068 transition == PageTransition::AUTO_BOOKMARK ||
#069 transition == PageTransition::GENERATED ||
#070 transition == PageTransition::START_PAGE) {
#071 // Don't forget the openers if this tab is a New Tab page opened at the
#072 // end of the TabStrip (e.g. by pressing Ctrl+T). Give the user one
#073 // navigation of one of these transition types before resetting the
#074 // opener relationships (this allows for the use case of opening a new
#075 // tab to do a quick look-up of something while viewing a tab earlier in
#076 // the strip). We can make this heuristic more permissive if need be.
#077 // TODO(beng): (http://b/1306495) write unit tests for this once this
#078 // object is unit-testable.
#079 int current_tab_index =
#080 tabstrip_model_.GetIndexOfTabContents(current_tab);
#081 bool forget_openers =
#082 !(current_tab->type() == TAB_CONTENTS_NEW_TAB_UI &&
#083 current_tab_index == (tab_count() - 1) &&
#084 current_tab->controller()->GetEntryCount() == 1);
#085 if (forget_openers) {
#086 // If the user navigates the current tab to another page in any way
#087 // other than by clicking a link, we want to pro-actively forget all
#088 // TabStrip opener relationships since we assume they're beginning a
#089 // different task by reusing the current tab.
#090 tabstrip_model_.ForgetAllOpeners();
#091 // In this specific case we also want to reset the group relationship,
#092 // since it is now technically invalid.
#093 tabstrip_model_.ForgetGroup(current_tab);
#094 }
#095 }

这里开始在当前TAB页里加载网络地址连接。
#096 current_tab->controller()->LoadURL(url, transition);
#097 // The TabContents might have changed as part of the navigation (ex: new tab
#098 // page can become WebContents).

获取当前显示的内容。
#099 new_contents = current_tab->controller()->active_contents();

隐藏最下面状态提示窗口。
#100 GetStatusBubble()->Hide();
#101
#102 // Synchronously update the location bar. This allows us to immediately
#103 // have the URL bar update when the user types something, rather than
#104 // going through the normal system of ScheduleUIUpdate which has a delay.
更新本地的工具条。
#105 UpdateToolBar(false);


后面的内容先不分析，主要分析目前打开当前连接的内容。
#106 } else if (disposition == OFF_THE_RECORD) {
#107 OpenURLOffTheRecord(profile_, url);
#108 return;
#109 } else if (disposition != SUPPRESS_OPEN) {
#110 new_contents =
#111 AddTabWithURL(url, transition, disposition != NEW_BACKGROUND_TAB,
#112 instance);
#113 }
#114
#115 if (disposition != NEW_BACKGROUND_TAB && source_tab_was_frontmost) {
#116 // Give the focus to the newly navigated tab, if the source tab was
#117 // front-most.
#118 new_contents->Focus();
#119 }
#120
#121 if (!override_encoding.empty()) {
#122 // The new tab needs a special encoding, such as a view source page
#123 // which should use the same encoding as the original page.
#124 WebContents* web_contents = new_contents->AsWebContents();
#125 if (web_contents)
#126 web_contents->set_override_encoding(override_encoding);
#127 }
#128 }
#129

上面函数的过程是这样的：主要根据打开网页的方式来选择窗口，比如是创建新窗口，还是只是打开一个TAB页，然后在TAB页显示。在这里还做了同一个网页地址的优化，不让它打开两个相同的进程来处理。
Browser对象是创建一个浏览器对象，接着调用LoadURL函数来加载输入的网页连接，隐藏当前窗口最下面的加载状态条，更新当前窗口的状态条，就完成了这个函数对当前TAB页加载网页的功能。下一次再来分析LoadURL函数是怎么样打开网页连接了。