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/logging.h"
   9 #include "base/supports_user_data.h"
  10 #include "ios/web/public/web_state/web_state.h"
  11
  12 namespace web {
  13
  14 // A base class for classes attached to, and scoped to, the lifetime of a
  15 // WebState. For example:
  16 //
  17 // --- in foo.h ---
  18 // class Foo : public web::WebStateUserData<Foo> {
  19 //  public:
  20 //   ~Foo() override;
  21 //   // ... more public stuff here ...
  22 //  private:
  23 //   explicit Foo(web::WebState* web_state);
  24 //   friend class web::WebStateUserData<Foo>;
  25 //   // ... more private stuff here ...
  26 // }
  27 // --- in foo.cc ---
  28 // DEFINE_WEB_CONTENTS_USER_DATA_KEY(Foo);
  29 //
  30 template <typename T>
  31 class WebStateUserData : public base::SupportsUserData::Data {
  32  public:
  33   // Creates an object of type T, and attaches it to the specified WebState.
  34   // If an instance is already attached, does nothing.
  35   static void CreateForWebState(WebState* web_state) {
  36     DCHECK(web_state);
  37     if (!FromWebState(web_state))
  38       web_state->SetUserData(UserDataKey(), new T(web_state));
  39   }
  40
  41   // Retrieves the instance of type T that was attached to the specified
  42   // WebState (via CreateForWebState above) and returns it. If no instance
  43   // of the type was attached, returns null.
  44   static T* FromWebState(WebState* web_state) {
  45     return static_cast<T*>(web_state->GetUserData(UserDataKey()));
  46   }
  47   static const T* FromWebState(const WebState* web_state) {
  48     return static_cast<const T*>(web_state->GetUserData(UserDataKey()));
  49   }
  50   // Removes the instance attached to the specified WebState.
  51   static void RemoveFromWebState(WebState* web_state) {
  52     web_state->RemoveUserData(UserDataKey());
  53   }
  54
  55  protected:
  56   static inline void* UserDataKey() { return &kLocatorKey; }
  57
  58  private:
  59   // The user data key.
  60   static int kLocatorKey;
  61 };
  62
  63 // The macro to define the locator key. This key should be defined in the .cc
  64 // file of the derived class.
  65 //
  66 // The "= 0" is surprising, but is required to effect a definition rather than
  67 // a declaration. Without it, this would be merely a declaration of a template
  68 // specialization. (C++98: 14.7.3.15; C++11: 14.7.3.13)
  69 //
  70 #define DEFINE_WEB_STATE_USER_DATA_KEY(TYPE) \
  71   template <>                                \
  72   int web::WebStateUserData<TYPE>::kLocatorKey = 0
  73
  74 }  // namespace web
  75
  76 #endif  // IOS_WEB_PUBLIC_WEB_STATE_WEB_STATE_USER_DATA_H_