C#高性能動態獲取物件屬性值

動態獲取物件的性能值，這個在開發程序中經常會遇到，這里我們探討一下何如高性能的獲取屬性值，為了對比測驗，我們定義一個類People

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

然后通過直接代碼呼叫方式來取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 =https://www.cnblogs.com/seriawei/archive/2020/12/08/ people.Name;
    }
    stopwatch.Stop();
    Console.WriteLine("Directly: {0}ms", stopwatch.ElapsedMilliseconds);
}

大概花了37ms:

反射

通過反射來獲取物件的屬性值，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 =https://www.cnblogs.com/seriawei/archive/2020/12/08/ 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？

動態構建Lambda

我們知道可以動態構建Linq的Lambda運算式，然后通過編譯后得到一個委托，如果能動態構建回傳屬性值的委托，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<People, object> 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");//引數m
    PropertyInfo property = type.GetProperty("Name");
    Expression expProperty = Expression.Property(parameter, property.Name);//取引數的屬性m.Name
    var propertyDelegateExpression = Expression.Lambda(expProperty, parameter);//變成運算式 m => m.Name
    var propertyDelegate = (Func<People, object>)propertyDelegateExpression.Compile();//編譯成委托
    Stopwatch stopwatch = Stopwatch.StartNew();
    for (int i = 0; i < 10000000; i++)
    {
        object value =https://www.cnblogs.com/seriawei/archive/2020/12/08/ propertyDelegate.Invoke(people);
    }
    stopwatch.Stop();
    Console.WriteLine("Lambda:{0}ms", stopwatch.ElapsedMilliseconds);
}

然后我們測驗一下，大概花了138ms，性能要比反射好非常多：

委托呼叫

雖然動態構建Lambda的性能已經很好了，但還是更好嗎？畢竟比直接呼叫還是差了一些，要是能直接呼叫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，可以通過呼叫這個方法來取得對應屬性的值，可以使用System.Delegate.CreateDelegate創建一個委托來呼叫這個方法，

• 通過委托呼叫方法來取得屬性值

我們定義一個MemberGetDelegate的委托，然后通過它來呼叫取值方法：

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 =https://www.cnblogs.com/seriawei/archive/2020/12/08/ memberGet(people);
    }
    stopwatch.Stop();
    Console.WriteLine("Delegate: {0}ms", stopwatch.ElapsedMilliseconds);
}

然后我們測驗一下，大概花了38ms，性能幾乎與直接呼叫一致：

最后做一個簡單的封裝，快取一下創建的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());
    }
}

這樣使用起來就方便多了

People people = new People { Name = "Wayne" };
PropertyValue<People> propertyValue = https://www.cnblogs.com/seriawei/archive/2020/12/08/new PropertyValue<People>(people);
object value = https://www.cnblogs.com/seriawei/archive/2020/12/08/propertyValue.Get("Name");

標籤：.NET技术

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