C Sharp与.net学习笔记(二)

看看动态库创建与使用相关的东西

生成与使用(托管的)dll

• dll.cs ==> dll.dll

// file: dll.cs
public class Calc
{
    public static int Add(int a, int b)
    {
        return a + b;
    }
}

• main.cs ==> main.exe

// file: main.cs
using System;

class App
{
    public static void Main()
    {
        Console.WriteLine("{0} + {1} = {2}", 123, 456, Calc.Add(123, 456));
    }
}

编译：

E:\> csc /target:library dll.cs
E:\> csc /reference:dll.dll  main.cs

运行：

E:\> main
123 + 456 = 579

动态加载dll

using System;
using System.Reflection;

class App
{
    public static void Main()
    {
        Assembly dll = Assembly.Load("dll");
        Type calcType = dll.GetType("Calc");
        object[] parameters = new object[]{123, 456};
        object res = calcType.InvokeMember("Add2",
                BindingFlags.Default | BindingFlags.InvokeMethod,
                null,
                null,
                parameters);
        Console.WriteLine("{0} + {1} = {2}", 123, 456, (int)res);
    }
}

• 首先，加载我们动态库dll.dll，使用的Assembly.Load，也可以用(相对或绝对路径)

Assembly.LoadFrom("dll.dll");

• 然后，获取需要的类型，存于calcType

• 最后通过InvokeMember调用该类型中的成员函数。如果调用的不是static成员，还需要创建该类型的实例

        Object obj = Activator.CreateInstance(calcType);
        object res = calcType.InvokeMember("Add",
                BindingFlags.Default | BindingFlags.InvokeMethod,
                null,
                obj,
                parameters);

另一种写法:

        MethodInfo addMethod = calcType.GetMethod("Add");
        object[] parameters = new object[]{123, 456};
        object obj = Activator.CreateInstance(calcType);
        object res = addMethod.Invoke(obj, parameters);

使用非托管 dll

• dll2.cpp ==> dll2.dll

// file: dll2.cpp
extern "C" int __declspec(dllexport) Add(int a, int b)
{
    return a + b;
}

• main.cs ==> main.exe

// file: main.cs
using System;
using System.Runtime.InteropServices;

class App
{
    [DllImport("dll2.dll")]
    public static extern int Add(int a, int b);

    public static void Main()
    {
        Console.WriteLine("{0} + {1} = {2}", 123, 456, Add(123, 456));
    }
}

编译运行：

E:\> cl dll2.cpp /LD
E:\> csc main.cs
E:\> main
123 + 456 = 579

这个东西被称为Platform Invoke(P/Invoke). DllImport还有一些属性

• EntryPoint

• CharSet

• CallingConvention

• SetLastError

[DllImport("dll2.dll", EntryPoint="Add", CharSet=CharSet.Auto, CallingConvention=CallingConvention.Winapi, SetLastError=true)]

动态加载dll

这又需要回到Win32 Api函数LoadLibrary、FreeLibrary这些东西了

// file: main.cs
using System;
using System.Runtime.InteropServices;

class App
{
    [DllImport("kernel32.dll")]
    public static extern IntPtr LoadLibrary(string dllFileName);

    [DllImport("kernel32.dll")]
    public static extern IntPtr GetProcAddress(IntPtr dllHandle, string functionName);

    [DllImport("kernel32.dll")]
    public static extern bool FreeLibrary(IntPtr dllHandle);

    private delegate int AddDelegate(int a, int b);

    public static void Main()
    {
        IntPtr handle = LoadLibrary("dll2.dll");
        IntPtr pAddFunc = GetProcAddress(handle, "Add");
        AddDelegate Add = (AddDelegate)Marshal.GetDelegateForFunctionPointer(
                pAddFunc, typeof(AddDelegate));

        Console.WriteLine("{0} + {1} = {2}", 123, 456, Add(123, 456));
        FreeLibrary(handle);
    }
}

先用P/Invoke把这3个函数弄进来，然后用它们去处理我们要动态加载的动态库。

直接编译

E:\> csc main.cs