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 != SAVE_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。