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
12namespace 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//
30template <typename T>
31class 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) \
72template<>                                      \
73int content::WebContentsUserData<TYPE>::kLocatorKey = 0
74
75}  // namespace content
76
77#endif  // CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_USER_DATA_H_
78