74 lines
2.3 KiB
C++
74 lines
2.3 KiB
C++
//
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// Copyright (C) 2014 The Android Open Source Project
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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#ifndef SHILL_PROPERTY_OBSERVER_H_
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#define SHILL_PROPERTY_OBSERVER_H_
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#include <memory>
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#include <base/callback.h>
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#include <base/macros.h>
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#include "shill/accessor_interface.h"
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#include "shill/error.h"
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#include "shill/property_observer_interface.h"
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namespace shill {
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// A templated object that retains a reference to a typed accessor,
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// and a saved value retrieved from the accessor. When the update
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// method is called, it compares its saved value to the current
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// value returned by the accessor. If the value has changed, it
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// calls the supplied callback and updates the saved value.
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template <class T>
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class PropertyObserver : public PropertyObserverInterface {
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public:
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typedef base::Callback<void(const T& new_value)> Callback;
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PropertyObserver(std::shared_ptr<AccessorInterface<T>> accessor,
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Callback callback)
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: accessor_(accessor), callback_(callback) {
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Error unused_error;
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saved_value_ = accessor_->Get(&unused_error);
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}
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~PropertyObserver() override {}
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// Implements PropertyObserverInterface. Compares the saved value with
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// what the Get() method of |accessor_| returns. If the value has changed
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// |callback_| is invoked and |saved_value_| is updated.
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void Update() override {
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Error error;
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T new_value_ = accessor_->Get(&error);
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if (!error.IsSuccess() || saved_value_ == new_value_) {
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return;
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}
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callback_.Run(new_value_);
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saved_value_ = new_value_;
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}
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private:
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friend class PropertyObserverTest;
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std::shared_ptr<AccessorInterface<T>> accessor_;
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Callback callback_;
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T saved_value_;
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DISALLOW_COPY_AND_ASSIGN(PropertyObserver);
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};
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} // namespace shill
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#endif // SHILL_PROPERTY_OBSERVER_H_
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