在blog上看到一篇文章《FxCop 的 ConstructorsShouldNotCallBaseClassVirtualMethods 規范 》原文：http://blog.csdn.net/xamcsdn2/archive/2004/08/11/71766.aspx

頗感興趣，寫了一段代碼研究（估計還稱不上研究，就當探索吧）了一下。

代碼如下。

using System;

namespace test_console
{

??? class baseclass
??? {
??????? public int count = 0;
??????? public baseclass()
??????? {
??????????? Console.WriteLine("Call BaseClass's Constructor Function...");
??????????? Increase("base");
??????? }

??????? public virtual void Increase(string type)
??????? {
??????????? Console.WriteLine(type);
??????????? Console.WriteLine("Call BaseClass's Increase Function...");
??????????? count ++;
??????? }
??? }

??? class subclass:baseclass
??? {
??????? public int subcount = 0;

??????? public subclass()
??????? {
??????????? Console.WriteLine("Call SubClass's Constructor Function...");
??????????? Console.WriteLine(subcount.ToString());
??????????? Increase("sub");
??????? }

??????? public override void Increase(string type)
??????? {
??????????? Console.WriteLine(type);
??????????? Console.WriteLine("Call SubClass's Increase Function...");
??????????? subcount ++;
??????????? Console.WriteLine(subcount.ToString());
??????? }
??????? ///
??????? /// 應用程序的主入口點。
??????? ///
??????? [STAThread]
??????? static void Main(string[] args)
??????? {
??????????? subclass c = new subclass();
??????????? Console.ReadLine();
??????? }
??? }
}


baseclass的構造函數調用了Increase()函數，subclass的構造函數同樣調用了此函數。運行結果如下：

Call BaseClass's Constructor Function...
base
Call SubClass's Increase Function...
1
Call SubClass's Constructor Function...
1
sub
Call SubClass's Increase Function...
2

可以看到SubClass的Increase函數被調用了兩次，我在subclass的increase中加入一個參數來判斷是由哪個構造函數來調用的，結果是先由baseclass調用，再由subclass調用。而且看上去似乎baseclass是先于subclass調用的，但是事實究竟如何呢？我們來看一下subclass的構造函數的IL代碼：

.method public hidebysig specialname rtspecialname instance void .ctor() cil managed
{
????? // Code Size: 51 byte(s)
????? .maxstack 2
????? L_0000: ldarg.0
????? L_0001: ldc.i4.0
????? L_0002: stfld int32 test_console.subclass::subcount
????? L_0007: ldarg.0
????? L_0008: call instance void test_console.baseclass::.ctor()
????? L_000d: ldstr "Call SubClass\'s Constructor Function..."
????? L_0012: call void [mscorlib]System.Console::WriteLine(string)
????? L_0017: ldarg.0
????? L_0018: ldflda int32 test_console.subclass::subcount
????? L_001d: call instance string int32::ToString()
????? L_0022: call void [mscorlib]System.Console::WriteLine(string)
????? L_0027: ldarg.0
????? L_0028: ldstr "sub"
????? L_002d: callvirt instance void test_console.baseclass::Increase(string)
????? L_0032: ret
}
一目了然，L_0008: call instance void test_console.baseclass::.ctor()在subclass的構造函數中先調用了baseclass的構造函數。

?

后記：作為面對對象程序設計者的基本知識，在這里談論子類構造函數先調用父類構造函數這一點似乎有點畫蛇添足，作為小弟的第一篇作品，希望能給那些初學者一些幫助吧。