IL查看override

江南才子

查看override的IL
Override示例
下面我们看一个Override的Example

namespace MyCollection
{
  public class MyBase
  {
    public virtual string Meth1()
    {
      return "MyBase-Meth1";
    }
    public virtual string Meth2()
    {
      return "MyBase-Meth2";
    }
    public virtual string Meth3()
    {
      return "MyBase-Meth3";
    }
  }
  class MyDerived : MyBase
  {
    // 使用 override 关键字重写虚方法 Meth1:
    public override string Meth1()
    {
      return "MyDerived-Meth1";
    }
    // 使用 new 关键字显式隐藏
    // 虚方法 Meth2:
    public new string Meth2()
    {
      return "MyDerived-Meth2";
    }
    // 由于下面声明中没有指定任何关键字
    // 因此将发出一个警告来提醒程序员
    // 此方法隐藏了继承的成员 MyBase.Meth3():
    public string Meth3()
    {
      return "MyDerived-Meth3";
    }
  }
  public class VirtualExample
  {
    public static void Main()
    {
      MyDerived mD = new MyDerived();
      MyBase mB = (MyBase)mD;
      System.Console.WriteLine(mD.Meth1());
      System.Console.WriteLine(mD.Meth2());
      System.Console.WriteLine(mD.Meth3());
      System.Console.WriteLine("以上为类MyDerived的显示结果！\n");
      System.Console.WriteLine(mB.Meth1());
      System.Console.WriteLine(mB.Meth2());
      System.Console.WriteLine(mB.Meth3());
      System.Console.WriteLine("以上为MyBase的显示结果！\n");
      System.Console.WriteLine("按任意键退出...");
      System.Console.ReadLine();
    }
  }
}

运行结果

IL查看
双击查看Main方法

IL代码

.method public hidebysig static void  Main() cil managed
{
  .entrypoint
  // Code size     121 (0x79)
  .maxstack  1
  .locals init ([0] class MyCollection.MyDerived mD,
       [1] class MyCollection.MyBase mB)
  IL_0000:  nop
  IL_0001:  newobj   instance void MyCollection.MyDerived::.ctor()
  IL_0006:  stloc.0
  IL_0007:  ldloc.0
  IL_0008:  stloc.1
  IL_0009:  ldloc.0
  IL_000a:  callvirt   instance string MyCollection.MyBase::Meth1()//调用的是MyBase的Meth1()
  IL_000f:  call     void [mscorlib]System.Console::WriteLine(string)
  IL_0014:  nop
  IL_0015:  ldloc.0
  IL_0016:  callvirt   instance string MyCollection.MyDerived::Meth2()
  IL_001b:  call     void [mscorlib]System.Console::WriteLine(string)
  IL_0020:  nop
  IL_0021:  ldloc.0
  IL_0022:  callvirt   instance string MyCollection.MyDerived::Meth3()
  IL_0027:  call     void [mscorlib]System.Console::WriteLine(string)
  IL_002c:  nop
  IL_002d:  ldstr    bytearray (E5 4E 0A 4E 3A 4E 7B 7C 4D 00 79 00 44 00 65 00   // .N.N:N{|M.y.D.e.
                  72 00 69 00 76 00 65 00 64 00 84 76 3E 66 3A 79   // r.i.v.e.d..v>f:y
                  D3 7E 9C 67 01 FF 0A 00 )             // .~.g....
  IL_0032:  call     void [mscorlib]System.Console::WriteLine(string)
  IL_0037:  nop
  IL_0038:  ldloc.1
  IL_0039:  callvirt   instance string MyCollection.MyBase::Meth1()//这里一样调用的是MyBase的Meth1()
  IL_003e:  call     void [mscorlib]System.Console::WriteLine(string)
  IL_0043:  nop
  IL_0044:  ldloc.1
  IL_0045:  callvirt   instance string MyCollection.MyBase::Meth2()
  IL_004a:  call     void [mscorlib]System.Console::WriteLine(string)
  IL_004f:  nop
  IL_0050:  ldloc.1
  IL_0051:  callvirt   instance string MyCollection.MyBase::Meth3()
  IL_0056:  call     void [mscorlib]System.Console::WriteLine(string)
  IL_005b:  nop
  IL_005c:  ldstr    bytearray (E5 4E 0A 4E 3A 4E 4D 00 79 00 42 00 61 00 73 00   // .N.N:NM.y.B.a.s.
                  65 00 84 76 3E 66 3A 79 D3 7E 9C 67 01 FF 0A 00 ) // e..v>f:y.~.g....
  IL_0061:  call     void [mscorlib]System.Console::WriteLine(string)
  IL_0066:  nop
  IL_0067:  ldstr    bytearray (09 63 FB 4E 0F 61 2E 95 00 90 FA 51 2E 00 2E 00   // .c.N.a.....Q....
                  2E 00 )                       // ..
  IL_006c:  call     void [mscorlib]System.Console::WriteLine(string)
  IL_0071:  nop
  IL_0072:  call     string [mscorlib]System.Console::ReadLine()
  IL_0077:  pop
  IL_0078:  ret

} // end of method VirtualExample::Main

IL解析
我们先回头看看源程序处的main内部的“System.Console.WriteLine(mD.Meth1());”语句对应上面的 IL_000a:  callvirt   instance string MyCollection.MyBase::Meth1() 和 IL_0039:  callvirt   instance string MyCollection.MyBase::Meth1()处的一模一样，原来它执行的是MyBase类的Meth1虚方法。而Meth1方法已经在 MyDerived类中重写了，所以这两个类的对应的方法1在本质说上都一样了。
通过看这个例子，我们能更加深入地理解override的功能了。看来ILdasm的确厉害，与其你想半天不如调IL代码看看，很多问题就会迎刃而解了，拨云见日啊！