web_contents_user_data.h | Explore in Territory

// Copyright 2012 The Chromium Authors
// 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/check.h"
#include "base/memory/ptr_util.h"
#include "base/memory/raw_ptr.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.
//
// When considering using this class, please carefully consider the intended
// lifetime of the data. There are other UserData classes which may more
// precisely match the intended lifetime. For example, DocumentUserData scopes
// the data to a document, NavigationHandleUserData to a navigation, etc. It is
// preferable to use a more specific UserData class, rather than storing
// non-WebContents state as a WebContentsUserData combined with using a
// WebContentsObserver to manually reset the state.
//
// For example:
//
// --- in foo_tab_helper.h ---
// class FooTabHelper : public content::WebContentsUserData<FooTabHelper> {
//  public:
//   ~FooTabHelper() override;
//
//   // ... more public stuff here ...
//
//  private:
//   explicit FooTabHelper(content::WebContents* contents);
//
//   friend WebContentsUserData;
//   WEB_CONTENTS_USER_DATA_KEY_DECL();
//
//   // ... more private stuff here ...
// };
//
// --- in foo_tab_helper.cc ---
// WEB_CONTENTS_USER_DATA_KEY_IMPL(FooTabHelper)
template <typename T>
class WebContentsUserData : public base::SupportsUserData::Data { … };

// This macro declares a static variable inside the class that inherits from
// WebContentsUserData The address of this static variable is used as the key to
// store/retrieve an instance of the class on/from a WebState.
#define WEB_CONTENTS_USER_DATA_KEY_DECL() …

// This macro instantiates the static variable declared by the previous macro.
// It must live in a .cc file to ensure that there is only one instantiation
// of the static variable.
#define WEB_CONTENTS_USER_DATA_KEY_IMPL(Type) …

// We tried using the address of a static local variable in UserDataKey() as a
// key instead of the address of a member variable. That solution allowed us to
// get rid of the macros above. Unfortately, each dynamic library that accessed
// UserDataKey() had its own instantiation of the method, resulting in different
// keys for the same WebContentsUserData type. Because of that, the solution was
// reverted. https://crbug.com/589840#c16

}  // namespace content

#endif  // CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_USER_DATA_H_
chromium/content/public/browser/web_contents_user_data.h
