TL；DR 版本：
使用DirectCast() 代替后期绑定或反射以获得更好的运行时性能。
这个问题让我很感兴趣。对于我编写的几乎所有应用程序，我都会定期使用DirectCast()。我一直使用它，因为它使 IntelliSense 工作，如果我不使用Option Strict On，那么我会在编译时出错。每隔一段时间，我会使用Option Strict Off，如果我很着急并且我正在测试一个设计概念，或者我急于为一次性问题提供快速而肮脏的解决方案。我从来没有考虑过使用它时的性能影响，因为我从来不用担心我写的东西的运行时性能。
想到这个问题让我有点好奇，所以我决定自己测试一下，看看有什么不同。我在 Visual Studio 中创建了一个新的控制台应用程序并开始工作。以下是该应用程序的完整源代码。如果您想自己查看结果，您应该可以直接复制/粘贴：
Option Strict Off
Option Explicit On
Imports System.Diagnostics
Imports System.Reflection
Imports System.IO
Imports System.Text
Module Module1
Const loopCntr As Int32 = 1000000
Const iterationCntr As Int32 = 5
Const resultPath As String = "C:\StackOverflow\DirectCastResults.txt"
Sub Main()
Dim objDirectCast As New MyObject("objDirectCast")
Dim objImplicitCasting As New MyObject("objImplicitCasting")
Dim objLateBound As New MyObject("objLateBound")
Dim objReflection As New MyObject("objReflection")
Dim objInvokeMember As New MyObject("objInvokeMember")
Dim sbElapsed As New StringBuilder : sbElapsed.Append("Running ").Append(iterationCntr).Append(" iterations for ").Append(loopCntr).AppendLine(" loops.")
Dim sbAverage As New StringBuilder : sbAverage.AppendLine()
AddHandler objDirectCast.ValueSet, AddressOf SetObjectDirectCast
AddHandler objImplicitCasting.ValueSet, AddressOf SetObjectImplictCasting
AddHandler objLateBound.ValueSet, AddressOf SetObjectLateBound
AddHandler objReflection.ValueSet, AddressOf SetObjectReflection
AddHandler objInvokeMember.ValueSet, AddressOf SetObjectInvokeMember
For Each myObj As MyObject In {objDirectCast, objImplicitCasting, objLateBound, objReflection, objInvokeMember}
Dim resultlist As New List(Of TimeSpan)
sbElapsed.AppendLine().Append("Time (seconds) elapsed for ").Append(myObj.Name).Append(" is: ")
For i = 1 To iterationCntr
Dim stpWatch As New Stopwatch
stpWatch.Start()
For _i = 0 To loopCntr
myObj.SetValue(_i)
Next
stpWatch.Stop()
sbElapsed.Append(stpWatch.Elapsed.TotalSeconds.ToString()).Append(", ")
resultlist.Add(stpWatch.Elapsed)
Console.WriteLine(myObj.Name & " is done.")
Next
Dim totalTicks As Long = 0L
resultlist.ForEach(Sub(x As TimeSpan) totalTicks += x.Ticks)
Dim averageTimeSpan As New TimeSpan(totalTicks / CLng(resultlist.Count))
sbAverage.Append("Average elapsed time for ").Append(myObj.Name).Append(" is: ").AppendLine(averageTimeSpan.ToString)
Next
Using strWriter As New StreamWriter(File.Open(resultPath, FileMode.Create, FileAccess.Write))
strWriter.WriteLine(sbElapsed.ToString)
strWriter.WriteLine(sbAverage.ToString)
End Using
End Sub
Sub SetObjectDirectCast(sender As Object, newValue As Int32)
Dim myObj As MyObject = DirectCast(sender, MyObject)
myObj.MyProperty = newValue
End Sub
Sub SetObjectImplictCasting(sender As Object, newValue As Int32)
Dim myObj As MyObject = sender
myObj.MyProperty = newValue
End Sub
Sub SetObjectLateBound(sender As Object, newValue As Int32)
sender.MyProperty = newValue
End Sub
Sub SetObjectReflection(sender As Object, newValue As Int32)
Dim pi As PropertyInfo = sender.GetType().GetProperty("MyProperty", BindingFlags.Public + BindingFlags.Instance)
pi.SetValue(sender, newValue, Nothing)
End Sub
Sub SetObjectInvokeMember(sender As Object, newValue As Int32)
sender.GetType().InvokeMember("MyProperty", BindingFlags.Instance + BindingFlags.Public + BindingFlags.SetProperty, Type.DefaultBinder, sender, {newValue})
End Sub
End Module
Public Class MyObject
Private _MyProperty As Int32 = 0
Public Event ValueSet(sender As Object, newValue As Int32)
Public Property Name As String
Public Property MyProperty As Int32
Get
Return _MyProperty
End Get
Set(value As Int32)
_MyProperty = value
End Set
End Property
Public Sub New(objName As String)
Me.Name = objName
End Sub
Public Sub SetValue(newvalue As Int32)
RaiseEvent ValueSet(Me, newvalue)
End Sub
End Class
我尝试在 Release 配置中运行应用程序，以及在没有附加 Visual Studio 调试器的情况下运行发布配置。以下是输出结果：
使用 Visual Studio 调试器发布：
Running 5 iterations for 1000000 loops.
Time (seconds) elapsed for objDirectCast is: 0.0214367, 0.0155618, 0.015561, 0.015544, 0.015542,
Time (seconds) elapsed for objImplicitCasting is: 0.014661, 0.0148947, 0.015051, 0.0149164, 0.0152732,
Time (seconds) elapsed for objLateBound is: 4.2572548, 4.2073932, 4.3517058, 4.480232, 4.4216707,
Time (seconds) elapsed for objReflection is: 0.3900658, 0.3833916, 0.3938861, 0.3875427, 0.4558457,
Time (seconds) elapsed for objInvokeMember is: 1.523336, 1.1675438, 1.1519875, 1.1698862, 1.2878384,
Average elapsed time for objDirectCast is: 00:00:00.0167291
Average elapsed time for objImplicitCasting is: 00:00:00.0149593
Average elapsed time for objLateBound is: 00:00:04.3436513
Average elapsed time for objReflection is: 00:00:00.4021464
Average elapsed time for objInvokeMember is: 00:00:01.2601184
发布不带 Visual Studio 调试器：
Running 5 iterations for 1000000 loops.
Time (seconds) elapsed for objDirectCast is: 0.0073776, 0.0055385, 0.0058196, 0.0059637, 0.0057557,
Time (seconds) elapsed for objImplicitCasting is: 0.0060359, 0.0056653, 0.0065522, 0.0063639, 0.0057324,
Time (seconds) elapsed for objLateBound is: 4.4858827, 4.1643164, 4.2380467, 4.1217441, 4.1270739,
Time (seconds) elapsed for objReflection is: 0.3828591, 0.3790779, 0.3849563, 0.3852133, 0.3847144,
Time (seconds) elapsed for objInvokeMember is: 1.0869766, 1.0808392, 1.0881596, 1.1139259, 1.0811786,
Average elapsed time for objDirectCast is: 00:00:00.0060910
Average elapsed time for objImplicitCasting is: 00:00:00.0060699
Average elapsed time for objLateBound is: 00:00:04.2274128
Average elapsed time for objReflection is: 00:00:00.3833642
Average elapsed time for objInvokeMember is: 00:00:01.0902160
看看这些结果，与添加转换的编译器相比，使用DirectCast() 几乎没有性能损失。但是，当依赖对象进行后期绑定时，会出现 HUGE 性能损失，并且执行速度会大大减慢。使用System.Reflection 时，直接投射对象会稍微变慢。我认为获得PropertyInfo 比使用.InvokeMember() 方法快得多是不寻常的。
结论：
尽可能使用DirectCast() 或直接投射对象。应该只在需要时才使用反射。仅将后期绑定的物品用作最后的手段。不过说实话，如果你只是在这里或那里修改一个对象几次，那么它在宏伟的计划中可能并不重要。
相反，您应该更关心这些方法如何失败以及如何防止它们这样做。例如，在SetObjectInvokeMember() 方法中，如果sender 对象没有MyProperty 属性，那么该位代码将引发异常。在SetObjectReflection() 方法中，返回的属性信息可能是nothing，这将导致NullReferenceException。