1 // Copyright (c) 2012 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_USER_DATA_H_ 6 #define CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_USER_DATA_H_ 7 8 #include "base/logging.h" 9 #include "base/supports_user_data.h" 10 #include "content/public/browser/web_contents.h" 11 12 namespace content { 13 14 // A base class for classes attached to, and scoped to, the lifetime of a 15 // WebContents. For example: 16 // 17 // --- in foo_tab_helper.h --- 18 // class FooTabHelper : public content::WebContentsUserData<FooTabHelper> { 19 // public: 20 // virtual ~FooTabHelper(); 21 // // ... more public stuff here ... 22 // private: 23 // explicit FooTabHelper(content::WebContents* contents); 24 // friend class content::WebContentsUserData<FooTabHelper>; 25 // // ... more private stuff here ... 26 // } 27 // --- in foo_tab_helper.cc --- 28 // DEFINE_WEB_CONTENTS_USER_DATA_KEY(FooTabHelper); 29 // 30 template <typename T> 31 class WebContentsUserData : public base::SupportsUserData::Data { 32 public: 33 // Creates an object of type T, and attaches it to the specified WebContents. 34 // If an instance is already attached, does nothing. 35 static void CreateForWebContents(WebContents* contents) { 36 DCHECK(contents); 37 if (!FromWebContents(contents)) 38 contents->SetUserData(UserDataKey(), new T(contents)); 39 } 40 41 // Retrieves the instance of type T that was attached to the specified 42 // WebContents (via CreateForWebContents above) and returns it. If no instance 43 // of the type was attached, returns NULL. 44 static T* FromWebContents(WebContents* contents) { 45 DCHECK(contents); 46 return static_cast<T*>(contents->GetUserData(UserDataKey())); 47 } 48 static const T* FromWebContents(const WebContents* contents) { 49 DCHECK(contents); 50 return static_cast<const T*>(contents->GetUserData(UserDataKey())); 51 } 52 53 protected: 54 static inline void* UserDataKey() { 55 return &kLocatorKey; 56 } 57 58 private: 59 // The user data key. 60 static int kLocatorKey; 61 }; 62 63 // The macro to define the locator key. This key must be defined in the .cc file 64 // of the tab helper otherwise different instances for different template types 65 // will be collapsed by the Visual Studio linker. 66 // 67 // The "= 0" is surprising, but is required to effect a definition rather than 68 // a declaration. Without it, this would be merely a declaration of a template 69 // specialization. (C++98: 14.7.3.15; C++11: 14.7.3.13) 70 // 71 #define DEFINE_WEB_CONTENTS_USER_DATA_KEY(TYPE) \ 72 template<> \ 73 int content::WebContentsUserData<TYPE>::kLocatorKey = 0 74 75 } // namespace content 76 77 #endif // CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_USER_DATA_H_ 78
