C#動態(tài)獲取對象屬性值，這才是高效正確的姿勢！
轉自：ZKEASOFT zkea.net/codesnippet/detail/csharp-fast-get-property-value.html
動態(tài)獲取對象的性能值，這個在開發(fā)過程中經(jīng)常會遇到，這里我們探討一下如何高性能的獲取屬性值。為了對比測試，我們定義一個類People
public class People
{
public string Name { get; set; }
}然后通過直接代碼調(diào)用方式來取1千萬次看要花多少時間：
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
通過反射來獲取對象的屬性值，這應該是大家常用的方式，但這種方式的性能比較差。接下來我們來看看同樣取1千萬次需要多少時間：
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，那還有沒有其它方式呢？
動態(tài)構建Lambda
我們知道可以動態(tài)構建Linq的Lambda表達式，然后通過編譯后得到一個委托，如果能動態(tài)構建返回屬性值的委托，就可以取到值了。所以我們想辦法構建一個像這樣的委托：
Func getName = m => m.Name; 接下來我們就通過Expression來構建：
private static void Lambda()
{
People people = new People { Name = "Wayne" };
Type type = typeof(People);
var parameter = Expression.Parameter(type, "m");//參數(shù)m
PropertyInfo property = type.GetProperty("Name");
Expression expProperty = Expression.Property(parameter, property.Name);//取參數(shù)的屬性m.Name
var propertyDelegateExpression = Expression.Lambda(expProperty, parameter);//變成表達式 m => m.Name
var propertyDelegate = (Funcobject >)propertyDelegateExpression.Compile();//編譯成委托
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);
}然后我們測試一下，大概花了138ms，性能要比反射好非常多：
委托調(diào)用
雖然動態(tài)構建Lambda的性能已經(jīng)很好了，但還是更好嗎？畢竟比直接調(diào)用還是差了一些，要是能直接調(diào)用屬性的取值方法就好了。
在C#中，可讀屬性都有一個對應的get_XXX()的方法，可以通過調(diào)用這個方法來取得對應屬性的值?？梢允褂肧ystem.Delegate.CreateDelegate創(chuàng)建一個委托來調(diào)用這個方法。
通過委托調(diào)用方法來取得屬性值
我們定義一個MemberGetDelegate的委托，然后通過它來調(diào)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);
}然后我們測試一下，大概花了38ms，性能幾乎與直接調(diào)用一致：
最后做一個簡單的封裝，緩存一下創(chuàng)建的Delegate
public class PropertyValue
{
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());
}
}這樣使用起來就方便多了
People people = new People { Name = "Wayne" };
PropertyValue propertyValue = new PropertyValue(people);
object value = propertyValue.Get("Name"); - EOF -
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