chrome ui源码剖析-ViewProp

 

先熟悉set的find原理

http://www.cnblogs.com/Clingingboy/p/3252136.html

这个类改造下,还是非常实用的,可以对于不同的类型做数据存储

一.ViewProp

// Copyright (c) 2011 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 UI_BASE_VIEW_PROP_H_
#define UI_BASE_VIEW_PROP_H_

namespace ui {

// ViewProp maintains a key/value pair for a particular view. ViewProp is
// designed as a replacement for the Win32's SetProp, but does not make use of
// window manager memory. ViewProp shares similar semantics as SetProp, the
// value for a particular view/key pair comes from the last ViewProp created.
class UI_EXPORT ViewProp {
 public:
  // Associates data with a view/key pair. If a ViewProp has already been
  // created for the specified pair |data| replaces the current value.
  //
  // ViewProp does *not* make a copy of the char*, the pointer is used for
  // sorting.
  ViewProp(gfx::AcceleratedWidget view, const char* key, void* data);
  ~ViewProp();

  // Returns the value associated with the view/key pair, or NULL if there is
  // none.
  static void* GetValue(gfx::AcceleratedWidget view, const char* key);

  // Returns the key.
  const char* Key() const;

 private:
  class Data;

  // Stores the actual data.
  scoped_refptr<Data> data_;
};

}  // namespace ui

#endif  // UI_BASE_VIEW_PROP_H_

二.实现

ViewProp::ViewProp(gfx::AcceleratedWidget view, const char* key, void* data) {
  Data::Get(view, key, true, &data_);
  data_->set_data(data);
}

ViewProp::~ViewProp() {
  // This is done to provide similar semantics to SetProp. In particular it's
  // assumed that ~ViewProp should behave as though RemoveProp was invoked.
  data_->set_data(NULL);
}

// static
void* ViewProp::GetValue(gfx::AcceleratedWidget view, const char* key) {
  scoped_refptr<Data> data;
  Data::Get(view, key, false, &data);
  return data.get() ? data->data() : NULL;
}

// static
const char* ViewProp::Key() const {
  return data_->key();
}

三.测试代码

TEST(ViewPropTest, Basic) {
    gfx::AcceleratedWidget nv1 = reinterpret_cast<gfx::AcceleratedWidget>(1);
    void* data1 = reinterpret_cast<void*>(11);
    // Register a value for a view/key pair.
    const char kKey1[] = "key_1";
    ViewProp prop(nv1, kKey1, data1);
    EXPECT_EQ(data1, ViewProp::GetValue(nv1, kKey1));
}

1. 构建一个ViewProp
2. 然后使用ViewProp::GetValue静态方法查找

四.Data类的实现

ViewProp构造函数用Data::Get创建Data,查找的时候还是用Data::Get方法,区别在于构造函数时创建,查找时不会创建

// Maints the actual view, key and data.
class ViewProp::Data : public base::RefCounted<ViewProp::Data> {
 public:
  // Returns the Data* for the view/key pair. If |create| is false and |Get|
  // has not been invoked for the view/key pair, NULL is returned.
  static void Get(gfx::AcceleratedWidget view,
                  const char* key,
                  bool create,
                  scoped_refptr<Data>* data) {
    if (!data_set_)
      data_set_ = new DataSet;
    scoped_refptr<Data> new_data(new Data(view, key));
    DataSet::const_iterator i = data_set_->find(new_data.get());
    if (i != data_set_->end()) {
      *data = *i;
      return;
    }
    if (!create)
      return;
    data_set_->insert(new_data.get());
    *data = new_data.get();
  }

  // The data.
  void set_data(void* data) { data_ = data; }
  void* data() const { return data_; }

  const char* key() const { return key_; }

 private:
  friend class base::RefCounted<Data>;

  // Used to order the Data in the map.
  class DataComparator {
   public:
    bool operator()(const Data* d1, const Data* d2) const {
      return (d1->view_ == d2->view_) ? (d1->key_ < d2->key_) :
                                        (d1->view_ < d2->view_);
    }
  };

  typedef std::set<Data*, DataComparator> DataSet;

  Data(gfx::AcceleratedWidget view, const char* key)
      : view_(view),
        key_(key),
        data_(NULL) {}

  ~Data() {
    DataSet::iterator i = data_set_->find(this);
    // Also check for equality using == as |Get| creates dummy values in order
    // to look up a value.
    if (i != data_set_->end() && *i == this)
      data_set_->erase(i);
  }

  // The existing set of Data is stored here. ~Data removes from the set.
  static DataSet* data_set_;

  const gfx::AcceleratedWidget view_;
  const char* key_;
  void* data_;

  DISALLOW_COPY_AND_ASSIGN(Data);
};

// static
ViewProp::Data::DataSet* ViewProp::Data::data_set_ = NULL;