ios/web/public/web_state/web_state_user_data.h

   1 // Copyright 2013 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 IOS_WEB_PUBLIC_WEB_STATE_WEB_STATE_USER_DATA_H_
   6 #define IOS_WEB_PUBLIC_WEB_STATE_WEB_STATE_USER_DATA_H_
   7
   8 #include "base/supports_user_data.h"
   9 #include "ios/web/public/web_state/web_state.h"
  10
  11 namespace web {
  12
  13 // A base class for classes attached to, and scoped to, the lifetime of a
  14 // WebState. For example:
  15 //
  16 // --- in foo.h ---
  17 // class Foo : public web::WebStateUserData<Foo> {
  18 //  public:
  19 //   ~Foo() override;
  20 //   // ... more public stuff here ...
  21 //  private:
  22 //   explicit Foo(web::WebState* web_state);
  23 //   friend class web::WebStateUserData<Foo>;
  24 //   // ... more private stuff here ...
  25 // }
  26 // --- in foo.cc ---
  27 // DEFINE_WEB_CONTENTS_USER_DATA_KEY(Foo);
  28 //
  29 template <typename T>
  30 class WebStateUserData : public base::SupportsUserData::Data {
  31  public:
  32   // Creates an object of type T, and attaches it to the specified WebState.
  33   // If an instance is already attached, does nothing.
  34   static void CreateForWebState(WebState* web_state) {
  35     if (!FromWebState(web_state))
  36       web_state->SetUserData(UserDataKey(), new T(web_state));
  37   }
  38
  39   // Retrieves the instance of type T that was attached to the specified
  40   // WebState (via CreateForWebState above) and returns it. If no instance
  41   // of the type was attached, returns null.
  42   static T* FromWebState(WebState* web_state) {
  43     return static_cast<T*>(web_state->GetUserData(UserDataKey()));
  44   }
  45   static const T* FromWebState(const WebState* web_state) {
  46     return static_cast<const T*>(web_state->GetUserData(UserDataKey()));
  47   }
  48   // Removes the instance attached to the specified WebState.
  49   static void RemoveFromWebState(WebState* web_state) {
  50     web_state->RemoveUserData(UserDataKey());
  51   }
  52
  53  protected:
  54   static inline void* UserDataKey() { return &kLocatorKey; }
  55
  56  private:
  57   // The user data key.
  58   static int kLocatorKey;
  59 };
  60
  61 // The macro to define the locator key. This key should be defined in the .cc
  62 // file of the derived class.
  63 //
  64 // The "= 0" is surprising, but is required to effect a definition rather than
  65 // a declaration. Without it, this would be merely a declaration of a template
  66 // specialization. (C++98: 14.7.3.15; C++11: 14.7.3.13)
  67 //
  68 #define DEFINE_WEB_STATE_USER_DATA_KEY(TYPE) \
  69   template <>                                \
  70   int web::WebStateUserData<TYPE>::kLocatorKey = 0
  71
  72 }  // namespace web
  73
  74 #endif  // IOS_WEB_PUBLIC_WEB_STATE_WEB_STATE_USER_DATA_H_