作为初学者来说，在C#中使用API确是一件令人头疼的问题。在使用API之间你必须知道如何在C#中使用结构、类型转换、安全/不安全代码，可控/不可控代码等许多知识。
一切从简单开始，复杂的大家一时不能接受。我们就从实现一个简单的MessageBox开始。首先打开VS.Net ，创建一个新的C#工程，并添加一个Button按钮。当这个按钮被点击，则显示一个MessageBox对话框。
即然我们需要引用外来库，所以必须导入一个Namespace：
using System.Runtime.InteropServices;
接着添加下面的代码来声明一个API：
[DllImport("User32.dll")]
public static extern int MessageBox(int h, string m, string c, int type);
此处DllImport属性被用来从不可控代码中调用一方法。”User32.dll”则设定了类库名。DllImport属性指定dll的位置，这个dll中包括调用的外部方法。Static修饰符则声明一个静态元素，而这个元素属于类型本身而不是上面指定的对象。extern则表示这个方法将在工程外部执行，使用DllImport导入的方法必须使用extern修饰符。
MessageBox 则是函数名，拥有4个参数，其返回值为数字。
大多数的API都能传递并返回值。
添中Click点击事件代码:
protected void button1_Click(object sender, System.EventArgs e)
{
MessageBox (0,"API Message Box","API Demo",0);
}
编译并运行这个程序，当你点击按钮后，你将会看到对话框，这便是你使用的API函数。
使用结构体
操作带有结构体的API比使用简单的API要复杂的多。但是一旦你掌握了API的过程，那个整个API世界将在你的掌握之中。
下面的例子中我们将使用GetSystemInfo API 来获取整个系统的信息。
第一步还是打开C#建立一个Form工程，同样的添中一个Button按钮，在代码窗中输入下面的代码，导入Namespace：
using System.Runtime.InteropServices;
声明一个结构体，它将做为GetSystemInfo的一个参数：
[StructLayout(LayoutKind.Sequential)]
public struct SYSTEM_INFO {
public uint dwOemId;
public uint dwPageSize;
public uint lpMinimumApplicationAddress;
public uint lpMaximumApplicationAddress;
public uint dwActiveProcessorMask;
public uint dwNumberOfProcessors;
public uint dwProcessorType;
public uint dwAllocationGranularity;
public uint dwProcessorLevel;
public uint dwProcessorRevision;
}
声明API函数:
[DllImport("kernel32")]
static extern void GetSystemInfo(ref SYSTEM_INFO pSI);
添加下面的代码至按钮的点击事件处理中：
首先创建一个SYSTEM_INFO结构体，并将其传递给GetSystemInfo函数。
protected void button1_Click (object sender, System.EventArgs e)
{
try
{
SYSTEM_INFO pSI = new SYSTEM_INFO();
GetSystemInfo(ref pSI);
//
//
//
一旦你接收到返回的结构体，那么就可以以返回的参数来执行操作了。
e.g.listBox1.InsertItem (0,pSI.dwActiveProcessorMask.ToString());:
//
//
//
}
catch(Exception er)
{
MessageBox.Show (er.Message);
}
}
//Created By Ajit Mungale
//程序补充 飞刀
namespace UsingAPI
{
using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.WinForms;
using System.Data;
using System.Runtime.InteropServices;
//Struct 收集系统信息
[StructLayout(LayoutKind.Sequential)]
public struct SYSTEM_INFO {
public uint dwOemId;
public uint dwPageSize;
public uint lpMinimumApplicationAddress;
public uint lpMaximumApplicationAddress;
public uint dwActiveProcessorMask;
public uint dwNumberOfProcessors;
public uint dwProcessorType;
public uint dwAllocationGranularity;
public uint dwProcessorLevel;
public uint dwProcessorRevision;
}
//struct 收集内存情况
[StructLayout(LayoutKind.Sequential)]
public struct MEMORYSTATUS
{
public uint dwLength;
public uint dwMemoryLoad;
public uint dwTotalPhys;
public uint dwAvailPhys;
public uint dwTotalPageFile;
public uint dwAvailPageFile;
public uint dwTotalVirtual;
public uint dwAvailVirtual;
}
public class Form1 : System.WinForms.Form
{
private System.ComponentModel.Container components;
private System.WinForms.MenuItem menuAbout;
private System.WinForms.MainMenu mainMenu1;
private System.WinForms.ListBox listBox1;
private System.WinForms.Button button1;
//获取系统信息
[DllImport("kernel32")]
static extern void GetSystemInfo(ref SYSTEM_INFO pSI);
//获取内存信息
[DllImport("kernel32")]
static extern void GlobalMemoryStatus(ref MEMORYSTATUS buf);
//处理器类型
public const int PROCESSOR_INTEL_386 = 386;
public const int PROCESSOR_INTEL_486 = 486;
public const int PROCESSOR_INTEL_PENTIUM = 586;
public const int PROCESSOR_MIPS_R4000 = 4000;
public const int PROCESSOR_ALPHA_21064 = 21064;
public Form1()
{
InitializeComponent();
}
public override void Dispose()
{
base.Dispose();
components.Dispose();
}
private void InitializeComponent()
{
this.components = new System.ComponentModel.Container ();
this.mainMenu1 = new System.WinForms.MainMenu ();
this.button1 = new System.WinForms.Button ();
this.listBox1 = new System.WinForms.ListBox ();
this.menuAbout = new System.WinForms.MenuItem ();
mainMenu1.MenuItems.All = new System.WinForms.MenuItem[1] {this.menuAbout};
button1.Location = new System.Drawing.Point (148, 168);
button1.Size = new System.Drawing.Size (112, 32);
button1.TabIndex = 0;
button1.Text = "&Get Info";
button1.Click += new System.EventHandler (this.button1_Click);
listBox1.Location = new System.Drawing.Point (20, 8);
listBox1.Size = new System.Drawing.Size (368, 147);
listBox1.TabIndex = 1;
menuAbout.Text = "&About";
menuAbout.Index = 0;
menuAbout.Click += new System.EventHandler (this.menuAbout_Click);
this.Text = "System Information - Using API";
this.MaximizeBox = false;
this.AutoScaleBaseSize = new System.Drawing.Size (5, 13);
this.MinimizeBox = false;
this.Menu = this.mainMenu1;
this.ClientSize = new System.Drawing.Size (408, 213);
this.Controls.Add (this.listBox1);
this.Controls.Add (this.button1);
}
protected void menuAbout_Click (object sender, System.EventArgs e)
{
Form abt=new about() ;
abt.ShowDialog();
}
protected void button1_Click (object sender, System.EventArgs e)
{
try
{
SYSTEM_INFO pSI = new SYSTEM_INFO();
GetSystemInfo(ref pSI);
string CPUType;
switch (pSI.dwProcessorType)
{
case PROCESSOR_INTEL_386 :
CPUType= "Intel 386";
break;
case PROCESSOR_INTEL_486 :
CPUType = "Intel 486" ;
break;
case PROCESSOR_INTEL_PENTIUM :
CPUType = "Intel Pentium";
break;
case PROCESSOR_MIPS_R4000 :
CPUType = "MIPS R4000";
break;
case PROCESSOR_ALPHA_21064 :
CPUType = "DEC Alpha 21064";
break;
default :
CPUType = "(unknown)";
}
listBox1.InsertItem (0,"Active Processor Mask :"+pSI.dwActiveProcessorMask.ToString());
listBox1.InsertItem (1,"Allocation Granularity :"+pSI.dwAllocationGranularity.ToString());
listBox1.InsertItem (2,"Number Of Processors :"+pSI.dwNumberOfProcessors.ToString());
listBox1.InsertItem (3,"OEM ID :"+pSI.dwOemId.ToString());
listBox1.InsertItem (4,"Page Size:"+pSI.dwPageSize.ToString());
listBox1.InsertItem (5,"Processor Level Value:"+pSI.dwProcessorLevel.ToString());
listBox1.InsertItem (6,"Processor Revision:"+ pSI.dwProcessorRevision.ToString());
listBox1.InsertItem (7,"CPU type:"+CPUType);
listBox1.InsertItem (8,"Maximum Application Address: "+pSI.lpMaximumApplicationAddress.ToString());
listBox1.InsertItem (9,"Minimum Application Address:" +pSI.lpMinimumApplicationAddress.ToString());
/************** 从 GlobalMemoryStatus 获取返回值****************/
MEMORYSTATUS memSt = new MEMORYSTATUS ();
GlobalMemoryStatus (ref memSt);
listBox1.InsertItem(10,"Available Page File :"+ (memSt.dwAvailPageFile/1024).ToString ());
listBox1.InsertItem(11,"Available Physical Memory : " + (memSt.dwAvailPhys/1024).ToString());
listBox1.InsertItem(12,"Available Virtual Memory:" + (memSt.dwAvailVirtual/1024).ToString ());
listBox1.InsertItem(13,"Size of structur :" + memSt.dwLength.ToString());
listBox1.InsertItem(14,"Memory In Use :"+ memSt.dwMemoryLoad.ToString());
listBox1.InsertItem(15,"Total Page Size :"+ (memSt.dwTotalPageFile/1024).ToString ());
listBox1.InsertItem(16,"Total Physical Memory :" + (memSt.dwTotalPhys/1024).ToString());
listBox1.InsertItem(17,"Total Virtual Memory :" + (memSt.dwTotalVirtual/1024).ToString ());
}
catch(Exception er)
{
MessageBox.Show (er.Message);
}
}
public static void Main(string[] args)
{
try
{
Application.Run(new Form1());
}
catch(Exception er)
{
MessageBox.Show (er.Message );
}
}
}
}
