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C#动态获取对象属性值,这才是高效正确的姿势!

发表日期:2021-01-24 10:26 文章编辑:John0King 浏览次数:343

 动态获取对象的性能值,这个在开发过程中经常会遇到,这里我们探讨一下如何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:

 

图片

 

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:

 

图片

 

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:

 

图片

 

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。

 

  • 通过委托调用方法来取得属性值

 

 

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:

 

图片

 

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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