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// Copyright 2020 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef CHROME_BROWSER_ANDROID_TAB_ANDROID_USER_DATA_H_
#define CHROME_BROWSER_ANDROID_TAB_ANDROID_USER_DATA_H_
#include "base/supports_user_data.h"
#include "chrome/browser/android/tab_android.h"
// A base class for classes attached to, and scoped to, the lifetime of a
// TabAndroid. For example:
//
// --- in foo_tab_helper.h ---
// class FooTabHelper : public web::TabAndroidUserData<FooTabHelper> {
// public:
// ~FooTabHelper() override;
// // ... more public stuff here ...
// private:
// explicit FooTabHelper(web::TabAndroid* tab);
// friend class web::TabAndroidUserData<FooTabHelper>;
// TAB_ANDROID_USER_DATA_KEY_DECL();
// // ... more private stuff here ...
// };
//
// --- in foo_tab_helper.cc ---
// TAB_ANDROID_USER_DATA_KEY_IMPL(FooTabHelper)
template <typename T>
class TabAndroidUserData : public base::SupportsUserData::Data {
public:
// Creates an object of type T, and attaches it to the specified TabAndroid.
// If an instance is already attached, does nothing.
static void CreateForTabAndroid(TabAndroid* tab) {
DCHECK(tab);
if (!FromTabAndroid(tab))
tab->SetUserData(UserDataKey(), base::WrapUnique(new T(tab)));
}
// Retrieves the instance of type T that was attached to the specified
// TabAndroid (via CreateForTabAndroid above) and returns it. If no instance
// of the type was attached, returns nullptr.
static T* FromTabAndroid(TabAndroid* tab) {
DCHECK(tab);
return static_cast<T*>(tab->GetUserData(UserDataKey()));
}
static const void* UserDataKey() { return &T::kUserDataKey; }
};
// This macro declares a static variable inside the class that inherits from
// TabAndroidUserData The address of this static variable is used as the key to
// store/retrieve an instance of the class on/from a TabAndroid.
#define TAB_ANDROID_USER_DATA_KEY_DECL() static const int kUserDataKey = 0
// 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 TAB_ANDROID_USER_DATA_KEY_IMPL(Type) const int Type::kUserDataKey;
#endif // CHROME_BROWSER_ANDROID_TAB_ANDROID_USER_DATA_H_
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