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// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_USER_DATA_H_
#define CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_USER_DATA_H_
#include "base/logging.h"
#include "base/supports_user_data.h"
#include "content/public/browser/web_contents.h"
namespace content {
// A base class for classes attached to, and scoped to, the lifetime of a
// WebContents. For example:
//
// --- in foo_tab_helper.h ---
// class FooTabHelper : public content::WebContentsUserData<FooTabHelper> {
// public:
// virtual ~FooTabHelper();
// // ... more public stuff here ...
// private:
// explicit FooTabHelper(content::WebContents* contents);
// friend class content::WebContentsUserData<FooTabHelper>;
// // ... more private stuff here ...
// }
// --- in foo_tab_helper.cc ---
// DEFINE_WEB_CONTENTS_USER_DATA_KEY(FooTabHelper);
//
template <typename T>
class WebContentsUserData : public base::SupportsUserData::Data {
public:
// Creates an object of type T, and attaches it to the specified WebContents.
// If an instance is already attached, does nothing.
static void CreateForWebContents(WebContents* contents) {
DCHECK(contents);
if (!FromWebContents(contents))
contents->SetUserData(UserDataKey(), new T(contents));
}
// Retrieves the instance of type T that was attached to the specified
// WebContents (via CreateForWebContents above) and returns it. If no instance
// of the type was attached, returns NULL.
static T* FromWebContents(WebContents* contents) {
DCHECK(contents);
return static_cast<T*>(contents->GetUserData(UserDataKey()));
}
static const T* FromWebContents(const WebContents* contents) {
DCHECK(contents);
return static_cast<const T*>(contents->GetUserData(UserDataKey()));
}
protected:
static inline void* UserDataKey() {
return &kLocatorKey;
}
private:
// The user data key.
static int kLocatorKey;
};
// The macro to define the locator key. This key must be defined in the .cc file
// of the tab helper otherwise different instances for different template types
// will be collapsed by the Visual Studio linker.
//
// The "= 0" is surprising, but is required to effect a definition rather than
// a declaration. Without it, this would be merely a declaration of a template
// specialization. (C++98: 14.7.3.15; C++11: 14.7.3.13)
//
#define DEFINE_WEB_CONTENTS_USER_DATA_KEY(TYPE) \
template<> \
int content::WebContentsUserData<TYPE>::kLocatorKey = 0
} // namespace content
#endif // CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_USER_DATA_H_
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