當我們根據自動提示，或者完全自己輸入連接后，再按下回車鍵，這時瀏覽器就會去打開網頁，或者去查找內容。那么瀏覽器是怎么樣實現這些功能的呢？又是怎么判斷去打開網頁，還是去打開 GOOGLE 的搜索引擎的呢？下面就來分析這部份的代碼，如下：

#001 ? bool AutocompleteEdit::OnKeyDownOnlyWritable(TCHAR key,

#002 ?????????????????????????????????????????????? UINT repeat_count,

#003 ?????????????????????????????????????????????? UINT flags) {

#004 ??? // NOTE: Annoyingly, ctrl-alt-<key> generates WM_KEYDOWN rather than

#005 ??? // WM_SYSKEYDOWN, so we need to check (flags & KF_ALTDOWN) in various places

#006 ??? // in this function even with a WM_SYSKEYDOWN handler.

#007 ?

#008 ??? int count = repeat_count;

#009 ??? switch (key) {

#010 ????? case VK_RETURN:

#011 ??????? AcceptInput((flags & KF_ALTDOWN) ? NEW_FOREGROUND_TAB : CURRENT_TAB,

#012 ??????????????????? false);

#013 ??????? return true;

#014 ?

#015 ????? case VK_UP:

#016 ??????? count = -count;

#017 ??????? // FALL THROUGH

#018 ???? ? case VK_DOWN:

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當用戶按下回車鍵，就會調用上面的函數 OnKeyDownOnlyWritable ，并且在 VK_RETURN 按鍵處理回車的事件，接著就是調用函數 AcceptInput 來處理。

這個函數的代碼如下：

#001 ? void AutocompleteEdit::AcceptInput(WindowOpenDisposition disposition,

#002 ???????????????????????????????????? bool for_drop) {

#003 ??? // Get the URL and transition type for the selected entry.

#004 ??? PageTransition::Type transition;

#005 ??? bool is_history_what_you_typed_match;

#006 ??? std::wstring alternate_nav_url;

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保存當前獲取的 URL 連接串。

#007 ??? const std::wstring url(GetURLForCurrentText(&transition,

#008 ??????????????????????????????????????????????? &is_history_what_you_typed_match,

#009 ??????????????????????????????????????????????? &alternate_nav_url));

#010 ??? if (url.empty())

#011 ????? return;

#012 ?

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判斷是否重新加載當前的網頁。

#013 ??? if (url == permanent_text_) {

#014 ??? ?? // When the user hit enter on the existing permanent URL, treat it like a

#015 ????? // reload for scoring purposes. ? We could detect this by just checking

#016 ????? // user_input_in_progress_, but it seems better to treat "edits" that end

#017 ????? // up leaving the URL unchanged (e.g. deleting the last character and then

#018 ????? // retyping it) as reloads too.

#019 ????? transition = PageTransition::RELOAD;

#020 ??? } else if (for_drop || ((paste_state_ != NONE) &&

#021 ??????????????????????????? is_history_what_you_typed_match)) {

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下面是打開一個新的連接。

#022 ????? // When the user pasted in a URL and hit enter, score it like a link click

#023 ????? // rather than a normal typed URL, so it doesn't get inline autocompleted

#024 ????? // as aggressively later.

#025 ????? transition = PageTransition::LINK;

#026 ??? }

#027 ?

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這里是調用 OpenURL 函數打開這個連接的內容。

#028 ??? OpenURL(url, disposition, transition, alternate_nav_url,

#029 ??????????? AutocompletePopupModel::kNoMatch,

#030 ??????????? is_keyword_hint_ ? std::wstring() : keyword_);

#031 ? }

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這段代碼的流程很清楚，就是先通過判斷按鍵輸入，是否按下回車鍵，如果是回車鍵就調用函數 AcceptInput 處理，然后在這個函數就判斷這個連接是否已經打開了，如果已經打開，只需要重新加載就行了，如果不是當前的，就是打開一個新的連接。下一次再來分析 OpenURL 函數是怎么樣通過連接來重新加載，還是打開一個新網頁。

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谷歌瀏覽器的源碼分析(12)