上一次介紹到怎么樣從其它地方返回搜索到的超級連接，現在就來分析一下使用搜索引擎去查找的類 SearchProvider ，它是通過搜索引擎來查找出來的，在這里是通過 GOOGLE 搜索引擎來查找出來。它的聲明如下：

#001 ? // Autocomplete provider for searches and suggestions from a search engine.

#002 ? //

#003 ? // After construction, the autocomplete controller repeatedly calls Start()

#004 ? // with some user input, each time expecting to receive a small set of the best

#005 ? // matches (either synchronously or asynchronously).

#006 ? //

#007 ? // Initially the provider creates a match that searches for the current input

#008 ? // text. ? It also starts a task to query the Suggest servers. ? When that data

#009 ? // comes back, the provider creates and returns matches for the best

#010 ? // suggestions.

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SearchProvider 類是繼承 AutocompleteProvider 和 URLFetcher 類， AutocompleteProvider 提供一個自動完成的結果， URLFetcher 主要提供從 URL 獲取數據和狀態。

#011 ? class SearchProvider : public AutocompleteProvider,

#012 ???????????????????????? public URLFetcher::Delegate {

#013 ?? public:

#014 ??? SearchProvider(ACProviderListener* listener, Profile* profile)

#015 ??????? : AutocompleteProvider(listener, profile, "Search"),

#016 ????????? last_default_provider_(NULL),

#017 ????????? fetcher_(NULL),

#018 ????????? history_request_pending_(false),

#019 ????????? have_history_results_(false),

#020 ????????? suggest_results_pending_(false),

#021 ????????? have_suggest_results_(false) {

#022 ??? }

#023 ?

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開始獲取。

#024 ??? // AutocompleteProvider

#025 ??? virtual void Start(const AutocompleteInput& input,

#026 ?????????????????????? bool minimal_changes,

#027 ?????????????????????? bool synchronous_only);

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停止查找。

#028 ??? virtual void Stop();

#029 ?

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當獲取到數據回來時響應。

#030 ??? // URLFetcher::Delegate

#031 ??? virtual void OnURLFetchComplete(const URLFetcher* source,

#032 ????????????????? ?????????????????? const GURL& url,

#033 ??????????????????????????????????? const URLRequestStatus& status,

#034 ??????????????????????????????????? int response_code,

#035 ??????????????????????????????????? const ResponseCookies& cookies,

#036 ????????????? ?????????????????????? const std::string& data);

#037 ?

#038 ?? private:

#039 ??? struct NavigationResult {

#040 ????? NavigationResult(const std::wstring& url, const std::wstring& site_name)

#041 ????????? : url(url),

#042 ??????????? site_name(site_name) {

#043 ????? }

#044 ?

#045 ????? // The URL.

#046 ????? std::wstring url;

#047 ?

#048 ????? // Name for the site.

#049 ????? std::wstring site_name;

#050 ??? };

#051 ?

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保存返回的結果。

#052 ??? typedef std::vector<std::wstring> SuggestResults;

#053 ??? typedef std::vector<NavigationResult> NavigationResults;

#054 ??? typedef std::vector<history::KeywordSearchTermVisit> HistoryResults;

#055 ??? typedef std::map<std::wstring, AutocompleteMatch> MatchMap;

#056 ?

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運行獲取搜索引擎數據。

#057 ??? // Called when timer_ expires.

#058 ??? void Run();

#059 ?

#060 ??? // Determines whether an asynchronous subcomponent query should run for the

#061 ??? // current input. ? If so, starts it if necessary; otherwise stops it.

#062 ??? // NOTE: These functions do not update |done_|. ? Callers must do so.

#063 ??? void StartOrStopHistoryQuery(bool minimal_changes, bool synchronous_only);

#064 ??? void StartOrStopSuggestQuery(bool minimal_changes, bool synchronous_only);

#065 ?

#066 ??? // Functions to stop the separate asynchronous subcomponents.

#067 ??? // NOTE: These functions do not update |done_|. ? Callers must do so.

#068 ??? void StopHistory();

#069 ??? void StopSuggest();

#070 ?

#071 ??? // Called back by the history system to return searches that begin with the

#072 ??? // input text.

#073 ??? void OnGotMostRecentKeywordSearchTerms(

#074 ??????? CancelableRequestProvider::Handle handle,

#075 ??????? HistoryResults* results);

#076 ?

#077 ??? // Parses the results from the Suggest server and stores up to kMaxMatches of

#078 ??? // them in server_results_. ? Returns whether parsing succeeded.

#079 ??? bool ParseSuggestResults(Value* root_val);

#080 ?

#081 ??? // Converts the parsed server results in server_results_ to a set of

#082 ??? // AutocompleteMatches and adds them to |matches_|. ? This also sets |done_|

#083 ??? // correctly.

#084 ??? void ConvertResultsToAutocompleteMatches();

#085 ?

#086 ??? // Determines the relevance for a particular match. ? We use different scoring

#087 ??? // algorithms for the different types of matches.

#088 ??? int CalculateRelevanceForWhatYouTyped() const;

#089 ??? // |time| is the time at which this query was last seen.

#090 ??? int CalculateRelevanceForHistory(const Time& time) const;

#091 ??? // |suggestion_value| is which suggestion this is in the list returned from

#092 ??? // the server; the best suggestion is suggestion number 0.

#093 ??? int CalculateRelevanceForSuggestion(size_t suggestion_value) const;

#094 ??? // |suggestion_value| is same as above.

#095 ??? int CalculateRelevanceForNavigation(size_t suggestion_value) const;

#096 ?

#097 ??? // Creates an AutocompleteMatch for "Search <engine> for |query_string|" with

#098 ??? // the supplied relevance. ? Adds this match to |map|; if such a match already

#099 ??? // exists, whichever one has lower relevance is eliminated.

#100 ??? void AddMatchToMap(const std::wstring& query_string,

#101 ?????????????????????? int relevance,

#102 ?????????????????????? int accepted_suggestion,

#103 ?????????????????????? MatchMap* map);

#104 ??? // Returns an AutocompleteMatch for a navigational suggestion.

#105 ??? AutocompleteMatch NavigationToMatch(const NavigationResult& query_string,

#106 ??????????????????????????????????????? int relevance);

#107 ?

#108 ??? // Trims "http:" and up to two subsequent slashes from |url|. ? Returns the

#109 ??? // number of characters that were trimmed.

#110 ??? // TODO( kochi ): this is duplicate from history_autocomplete

#111 ??? static size_t TrimHttpPrefix(std::wstring* url);

#112 ?

#113 ??? // Don't send any queries to the server until some time has elapsed after

#114 ??? // the last keypress, to avoid flooding the server with requests we are

#115 ??? // likely to end up throwing away anyway.

#116 ??? static const int kQueryDelayMs;

#117 ?

#118 ??? // The user's input.

#119 ??? AutocompleteInput input_;

#120 ?

#121 ??? TemplateURL default_provider_; ? // Cached across the life of a query so we

#122 ??????????????????????????????????? // behave consistently even if the user

#123 ??????????????????????????????????? // changes their default while the query is

#124 ????????????? ?????????????????????? // running.

#125 ??? const TemplateURL* last_default_provider_;

#126 ??????????????????????????????????? // TODO(pkasting): http://b/1162970 ? We

#127 ??????????????????????????????????? // shouldn't need this.

#128 ?

#129 ??? // An object we can use to cancel history requests.

#130 ??? CancelableRequestConsumer history_request_consumer_;

#131 ?

#132 ??? // Searches in the user's history that begin with the input text.

#133 ??? HistoryResults history_results_;

#134 ?

#135 ??? // Whether history_results_ is valid (so we can tell invalid apart from

#136 ??? // empty).

#137 ??? bool have_history_results_;

#138 ?

#139 ??? // Whether we are waiting for a history request to finish.

#140 ??? bool history_request_pending_;

#141 ?

#142 ??? // True if we're expecting suggest results that haven't yet arrived. ? This

#143 ??? // could be because either |timer_| or |fetcher| is still running (see below).

#144 ??? bool suggest_results_pending_;

#145 ?

#146 ??? // A timer to start a query to the suggest server after the user has stopped

#147 ??? // typing for long enough.

#148 ??? base::OneShotTimer<SearchProvider> timer_;

#149 ?

#150 ??? // The fetcher that retrieves suggest results from the server.

#151 ??? scoped_ptr<URLFetcher> fetcher_;

#152 ?

#153 ??? // Suggestions returned by the Suggest server for the input text.

#154 ??? SuggestResults suggest_results_;

#155 ?

#156 ??? // Navigational suggestions returned by the server.

#157 ??? NavigationResults navigation_results_;

#158 ?

#159 ??? // Whether suggest_results_ is valid.

#160 ??? bool have_suggest_results_;

#161 ?

#162 ??? DISALLOW_EVIL_CONSTRUCTORS(SearchProvider);

#163 ? };

#164 ?

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在這個類里先調用函數 SearchProvider::Start 來獲取缺省的搜索引擎，然后停止以前的搜索，接著 SearchProvider::Run() 函數里使用 URLFetcher 獲取數據回來，它的代碼如下：

#001 ?? void SearchProvider::Run() {

#002 ??? // Start a new request with the current input.

#003 ??? DCHECK(!done_);

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獲取搜索的 URL 。

#004 ??? const TemplateURLRef* const suggestions_url =

#005 ??????? default_provider_.suggestions_url();

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建議代替的字符。

#006 ??? DCHECK(suggestions_url->SupportsReplacement());

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開始新的搜索。

#007 ??? fetcher_.reset(new URLFetcher(GURL(suggestions_url->ReplaceSearchTerms(

#008 ??????? default_provider_, input_.text(),

#009 ??????? TemplateURLRef::NO_SUGGESTIONS_AVAILABLE, std::wstring())),

#010 ??????? URLFetcher::GET, this));

#011 ??? fetcher_->set_request_context(profile_->GetRequestContext());

#012 ??? fetcher_->Start();

#013 ? }

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當前上面的搜索完成時，就會通知 SearchProvider::OnURLFetchComplete 函數來分析返回的結果，最后調用 SearchProvider::ConvertResultsToAutocompleteMatches() 函數來把結果轉換自動完成的列表項。

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通過上面的分析，就了解通過 GOOGLE 搜索引擎自動完成功能的實現。

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