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上一次說到需要調用這個 OpenURLFromTab 函數，那么這個函數是做什么的呢？從名稱上可能猜到它是打開網頁，但是是從目前 TAB 頁里打開呢？還是新建一個？或者使用每個 TAB 頁一個進程呢？這些疑惑，只能通過代碼的分析來理解它的實現，代碼如下：

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這個函數的參數意思：

source 是 TAB 內容。

url 是網絡連接地址。

disposition 是窗口打開的位置。

transition 是連接傳送的類型。

override_encoding 是編碼類型。

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#001 ? void Browser::OpenURLFromTab(TabContents* source,

#002 ?????????????????????????????? const GURL& url,

#003 ?????????????????????????????? WindowOpenDisposition disposition,

#004 ?????????????????????????????? PageTransition::Type transition,

#005 ?????????????????????????????? const std::string& override_encoding) {

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調試時檢查代碼。

#006 ??? // No code for these yet

#007 ??? DCHECK((disposition != NEW_POPUP) && (disposition != SAVE_TO_DISK));

#008 ?

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獲取當前的 TAB 頁。

#009 ??? TabContents* current_tab = source ? source : GetSelectedTabContents();

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判斷是否當前 TAB 頁選中。

#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?

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保存打開連接的實例指針。

#020 ??? SiteInstance* instance = NULL;

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如果不使用每個 TAB 頁一個進程的方式，就不需要進行下面的處理。因為同一個連接在一個進程里打開是比較快，這里主要做優化。

#021 ??? // Don't use this logic when "--process-per-tab" is specified.

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判斷是否有每一個 TAB 一個進程的方式。

#022 ??? if (!CommandLine().HasSwitch(switches::kProcessPerTab)) {

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有當前進程頁。

#023 ????? if (current_tab) {

#024 ??????? const WebContents* const web_contents = current_tab->AsWebContents();

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判斷是否相同的網絡連接地址。

#025 ??????? if (web_contents) {

#026 ????????? const GURL& current_url = web_contents->GetURL();

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如果相同的網絡地址，并且有實例打開，就返回這個實例在 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.

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下面進行不打開新窗口的處理。

#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 ?

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這里開始處理打開一個新窗口顯示網絡連接。

#061 ??? if (disposition == NEW_WINDOW) {

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創建一個新的 Browser 瀏覽器對象。

#062 ????? Browser* new_browser = new Browser(gfx::Rect(), SW_SHOWNORMAL, profile_,

#063 ???????????????????????????????????????? BrowserType::TABBED_BROWSER, L"");

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創建一個 TAB 內容。

#064 ????? new_contents = new_browser->AddTabWithURL(url, transition, true, instance);

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這里開始顯示這個網絡連接的內容。

#065 ????? new_browser->Show();

#066 ??? } else if ((disposition == CURRENT_TAB) && current_tab) {

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下面開始在當前 TAB 頁里打開連接，同時判斷處理的類型。

#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 ????? }

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這里開始在當前 TAB 頁里加載網絡地址連接。

#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).

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獲取當前顯示的內容。

#099 ????? new_contents = current_tab->controller()->active_contents();

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隱藏最下面狀態提示窗口。

#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.

更新本地的工具條。

#105 ????? UpdateToolBar(false);

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后面的內容先不分析，主要分析目前打開當前連接的內容。

#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 ?

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上面函數的過程是這樣的：主要根據打開網頁的方式來選擇窗口，比如是創建新窗口，還是只是打開一個 TAB 頁，然后在 TAB 頁顯示。在這里還做了同一個網頁地址的優化，不讓它打開兩個相同的進程來處理。

Browser 對象是創建一個瀏覽器對象，接著調用 LoadURL 函數來加載輸入的網頁連接，隱藏當前窗口最下面的加載狀態條，更新當前窗口的狀態條，就完成了這個函數對當前 TAB 頁加載網頁的功能。下一次再來分析 LoadURL 函數是怎么樣打開網頁連接了。

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谷歌瀏覽器的源碼分析(16)