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();
}
}
}
以上为程序运行的输出结果
双击查看Main方法
IL代码如下：
.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
对于IL代码指令的具体含义请参考：http://www.cnblogs.com/zery/p/3366175.html
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！
时间： 2024-10-28 21:35:27