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C#高性能动态获取对象属性值的步骤

ZKEASOFT 人气:0

动态获取对象的性能值,这个在开发过程中经常会遇到,这里我们探讨一下何如高性能的获取属性值。为了对比测试,我们定义一个类People

public class People
{
  public string Name { get; set; }
}

然后通过直接代码调用方式来取1千万次看要花多少时间:

private static void Directly()
{
  People people = new People { Name = "Wayne" };
  Stopwatch stopwatch = Stopwatch.StartNew();
  for (int i = 0; i < 10000000; i++)
  {
    object value = people.Name;
  }
  stopwatch.Stop();
  Console.WriteLine("Directly: {0}ms", stopwatch.ElapsedMilliseconds);
}

大概花了37ms:

反射
通过反射来获取对象的属性值,这应该是大家常用的方式,但这种方式的性能比较差。接下来我们来看看同样取1千万次需要多少时间:

private static void Reflection()
{
  People people = new People { Name = "Wayne" };
  Type type = typeof(People);
  PropertyInfo property = type.GetProperty("Name");
  Stopwatch stopwatch = Stopwatch.StartNew();
  for (int i = 0; i < 10000000; i++)
  {
    object value = property.GetValue(people);
  }
  stopwatch.Stop();
  Console.WriteLine("Reflection: {0}ms", stopwatch.ElapsedMilliseconds);
}

大概花了1533ms,果然要慢很多:

那既然反射慢,那还有没有其它方式呢?

动态构建Lambda
我们知道可以动态构建Linq的Lambda表达式,然后通过编译后得到一个委托,如果能动态构建返回属性值的委托,就可以取到值了。所以我们想办法构建一个像这样的委托:

Func<People, object> getName = m => m.Name;

接下来我们就通过Expression来构建:

private static void Lambda()
{
  People people = new People { Name = "Wayne" };
  Type type = typeof(People);
  var parameter = Expression.Parameter(type, "m");//参数m
  PropertyInfo property = type.GetProperty("Name");
  Expression expProperty = Expression.Property(parameter, property.Name);//取参数的属性m.Name
  var propertyDelegateExpression = Expression.Lambda(expProperty, parameter);//变成表达式 m => m.Name
  var propertyDelegate = (Func<People, object>)propertyDelegateExpression.Compile();//编译成委托
  Stopwatch stopwatch = Stopwatch.StartNew();
  for (int i = 0; i < 10000000; i++)
  {
    object value = propertyDelegate.Invoke(people);
  }
  stopwatch.Stop();
  Console.WriteLine("Lambda:{0}ms", stopwatch.ElapsedMilliseconds);
}

然后我们测试一下,大概花了138ms,性能要比反射好非常多:

委托调用

虽然动态构建Lambda的性能已经很好了,但还是更好吗?毕竟比直接调用还是差了一些,要是能直接调用属性的取值方法就好了。

在C#中,可读属性都有一个对应的get_XXX()的方法,可以通过调用这个方法来取得对应属性的值。可以使用System.Delegate.CreateDelegate创建一个委托来调用这个方法。

我们定义一个MemberGetDelegate的委托,然后通过它来调用取值方法:

delegate object MemberGetDelegate(People p);
private static void Delegate()
{
  People people = new People { Name = "Wayne" };
  Type type = typeof(People);
  PropertyInfo property = type.GetProperty("Name");
  MemberGetDelegate memberGet = (MemberGetDelegate)System.Delegate.CreateDelegate(typeof(MemberGetDelegate), property.GetGetMethod());
  Stopwatch stopwatch = Stopwatch.StartNew();
  for (int i = 0; i < 10000000; i++)
  {
    object value = memberGet(people);
  }
  stopwatch.Stop();
  Console.WriteLine("Delegate: {0}ms", stopwatch.ElapsedMilliseconds);
}

然后我们测试一下,大概花了38ms,性能几乎与直接调用一致:

最后做一个简单的封装,缓存一下创建的Delegate

public class PropertyValue<T>
{
  private static ConcurrentDictionary<string, MemberGetDelegate> _memberGetDelegate = new ConcurrentDictionary<string, MemberGetDelegate>();
  delegate object MemberGetDelegate(T obj);
  public PropertyValue(T obj)
  {
    Target = obj;
  }
  public T Target { get; private set; }
  public object Get(string name)
  {
    MemberGetDelegate memberGet = _memberGetDelegate.GetOrAdd(name, BuildDelegate);
    return memberGet(Target);
  }
  private MemberGetDelegate BuildDelegate(string name)
  {
    Type type = typeof(T);
    PropertyInfo property = type.GetProperty(name);
    return (MemberGetDelegate)Delegate.CreateDelegate(typeof(MemberGetDelegate), property.GetGetMethod());
  }
}

这样使用起来就方便多了

People people = new People { Name = "Wayne" };
PropertyValue<People> propertyValue = new PropertyValue<People>(people);
object value = propertyValue.Get("Name");

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