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    WPF 属性系统 依赖属性之内存占用分析

    出处：richieyang

    关于WPF的属性系统园子内有不少这方面的文章。里面大都提到了WPF依赖属性的在内存方面的优化。但是里面大都一笔带过。那么WPF到底是怎么样节约内存的。我们通过WPF属性和普通的CLR属性对比来看一下WPF属性在节约内存方面的优势在哪里。

    普通的CLR属性

    public partial class WindowMemory : Window
{
 　 Student0 stu;
 　 public WindowMemory()
　　{
　　　　InitializeComponent();
　　　　List<Student0> list = new List<Student0>();
　　　　for (int i = 0; i < 10000000; i++)
　　　　{
　　　　stu = new Student0();
　　　　list.Add(stu);
　　　　}
　　}
}
    public class Student0
    {
        public double Name { get; set; }
        public double Name1 { get; set; }
        public double Name2 { get; set; }
        public double Name3 { get; set; }
        public double Name4 { get; set; }
        public double Name5 { get; set; }
        public double Name6 { get; set; }
        public double Name7 { get; set; }
        public double Name8 { get; set; }
        public double Name9 { get; set; }
        public double Name10 { get; set; }
    }

    我们声明一个Student0类，里面放入十个属性。之后呢new 一千万个student 的实例加载到内存中。在任务管理器中看一下内存占用。

    我们看到程序大概占用了一个G的内存。计算一下。因为c#中的属性是通过get set方法对一个私有字段的封装，也就是说这个类里面有十个double类型的私有字段。double类型占8个字节。一兆是1048576个字节，131072个double类型。一千万个double大概占用76兆的内存。我们这儿声明了十个也就是760兆。另外还有student对象占用的内存。所以这儿程序占用内存大概是一个G;

    依赖属性

    public class Student0 : DependencyObject
    {
        public double Name
        {
            get
            {
                return (double)GetValue(NameProperty);
            }
            set
            {
                SetValue(NameProperty, value);
            }
        }
        public double Name1
        {
            get
            {
                return (double)GetValue(Name1Property);
            }
            set
            {
                SetValue(Name1Property, value);
            }
        }
        public double Name2
        {
            get
            {
                return (double)GetValue(Name2Property);
            }
            set
            {
                SetValue(Name2Property, value);
            }
        }
        public double Name3
        {
            get
            {
                return (double)GetValue(Name3Property);
            }
            set
            {
                SetValue(Name3Property, value);
            }
        }

        public double Name4
        {
            get
            {
                return (double)GetValue(Name4Property);
            }
            set
            {
                SetValue(Name4Property, value);
            }
        }
        public double Name5
        {
            get
            {
                return (double)GetValue(Name5Property);
            }
            set
            {
                SetValue(Name5Property, value);
            }
        }
        public double Name6
        {
            get
            {
                return (double)GetValue(Name6Property);
            }
            set
            {
                SetValue(Name6Property, value);
            }
        }

        public double Name7
        {
            get
            {
                return (double)GetValue(Name7Property);
            }
            set
            {
                SetValue(Name7Property, value);
            }
        }
        public double Name8
        {
            get
            {
                return (double)GetValue(Name8Property);
            }
            set
            {
                SetValue(Name8Property, value);
            }
        }
        public double Name9
        {
            get
            {
                return (double)GetValue(Name9Property);
            }
            set
            {
                SetValue(Name9Property, value);
            }
        }
        public double Name10
        {
            get
            {
                return (double)GetValue(Name10Property);
            }
            set
            {
                SetValue(Name10Property, value);
            }
        }public static readonly DependencyProperty NameProperty = DependencyProperty.Register("Name", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
        public static readonly DependencyProperty Name1Property = DependencyProperty.Register("Name1", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
        public static readonly DependencyProperty Name2Property = DependencyProperty.Register("Name2", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
        public static readonly DependencyProperty Name3Property = DependencyProperty.Register("Name3", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
        public static readonly DependencyProperty Name4Property = DependencyProperty.Register("Name4", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
        public static readonly DependencyProperty Name5Property = DependencyProperty.Register("Name5", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
        public static readonly DependencyProperty Name6Property = DependencyProperty.Register("Name6", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
        public static readonly DependencyProperty Name7Property = DependencyProperty.Register("Name7", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
        public static readonly DependencyProperty Name8Property = DependencyProperty.Register("Name8", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
        public static readonly DependencyProperty Name9Property = DependencyProperty.Register("Name9", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
        public static readonly DependencyProperty Name10Property = DependencyProperty.Register("Name10", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
    }

    我们把student类修改为依赖对象，在里面实现十个依赖属性，此时来查看一下内存占用

    此时只有三百多兆的内存占用。那么WPF的属性到底是如何节约内存的呢。因为CLR属性是在实例声明的时候就分配好了内存空间的。所以就算实例里面没有写入值，或者仍然是默认值，仍然会分配好内存空间。但是WPF的依赖属性不同。wpf的依赖属性是如下声明的

    public static readonly DependencyProperty NameProperty = DependencyProperty.Register("Name", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));

    注意上面的这条语句才是依赖属性的声明。而类似下面这样的是我们通过clr属性对依赖属性NameProperty进行了包装，使我们访问起来更方便。就想普通的属性那样。

    public double Name
{
      get
      {
          return (double)GetValue(NameProperty);
      }
      set
     {
         SetValue(NameProperty, value);
     }
}

    也就是说我们其实可以直接这样来声明Student0对象

    public class Student0 : DependencyObject
    {
        public static readonly DependencyProperty NameProperty = DependencyProperty.Register("Name", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
        public static readonly DependencyProperty Name1Property = DependencyProperty.Register("Name1", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
        public static readonly DependencyProperty Name2Property = DependencyProperty.Register("Name2", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
        public static readonly DependencyProperty Name3Property = DependencyProperty.Register("Name3", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
        public static readonly DependencyProperty Name4Property = DependencyProperty.Register("Name4", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
        public static readonly DependencyProperty Name5Property = DependencyProperty.Register("Name5", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
        public static readonly DependencyProperty Name6Property = DependencyProperty.Register("Name6", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
        public static readonly DependencyProperty Name7Property = DependencyProperty.Register("Name7", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
        public static readonly DependencyProperty Name8Property = DependencyProperty.Register("Name8", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
        public static readonly DependencyProperty Name9Property = DependencyProperty.Register("Name9", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
        public static readonly DependencyProperty Name10Property = DependencyProperty.Register("Name10", typeof(double), typeof(Student0), new PropertyMetadata((double)55.55));
    }

    之后呢通过setvalue,getvalue来存取值

    注意其实依赖属性的声明，在这里或者用注册来形容更贴切，只是一个入口点。也就是我们平常常说的单例模式。属性的值其实都放在依赖对象的一个哈希表里面。这里资料很多，大家随便找下就可以找到。

    所以依赖属性正在节约内存就在于这儿的依赖属性是一个static readonly 属性。所以不需要在对象每次实例化的时候都分配相关属性的内存空间，而是提供一个入口点。

    知道了这些我们再看一个没什么实际意义的例子。将student0对象修改如下。

    public class Student0
    {
        public double Name { get { return 1.00; } set { Name = 1.00; } }
        public double Name1 { get { return 1.00; } set { Name1 = 1.00; } }
        public double Name2 { get { return 1.00; } set { Name2 = 1.00; } }
        public double Name3 { get { return 1.00; } set { Name3 = 1.00; } }
        public double Name4 { get { return 1.00; } set { Name4 = 1.00; } }
        public double Name5 { get { return 1.00; } set { Name5 = 1.00; } }
        public double Name6 { get { return 1.00; } set { Name6 = 1.00; } }
        public double Name7 { get { return 1.00; } set { Name7 = 1.00; } }
        public double Name8 { get { return 1.00; } set { Name8 = 1.00; } }
        public double Name9 { get { return 1.00; } set { Name9 = 1.00; } }
        public double Name10 { get { return 1.00; } set { Name10 = 1.00; } }
    }

    此时程序只占用了不到200兆内存。因为属性的本质其实就是一个get set 方法。而方法是不需要实例化的，只需要一个指针指向就可以了。这儿我没没有在属性get;set;这种简化写法下声明的私有字段。所以没有了这些私有字段占用的内存。内存占用大大减少。

    仔细对比我们就会发现。wpf的属性系统真的没有特别设计来优化内存。只是这种提供入口点的方式顺带就减少了内存的占用。

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