一切從簡單開始，復雜的大家一時不能接受。我們就從實現一個簡單的MessageBox開始。首先打開VS.Net ，創建一個新的C#工程，並添加一個Button按鈕。當這個按鈕被點擊，則顯示一個MessageBox對話框。
即然我們需要引用外來庫，所以必須導入一個Namespace：
using System.Runtime.InteropServices;
接著添加下面的代碼來聲明一個API：
[DllImport("User32.dll")]
public static extern int MessageBox(int h, string m, string c, int type);
此處DllImport屬性被用來從不可控代碼中調用一方法。”User32.dll”則設定了類庫名。DllImport屬性指定dll的位置，這個dll中包括調用的外部方法。Static修飾符則聲明一個靜態元素，而這個元素屬於類型本身而不是上面指定的對象。extern則表示這個方法將在工程外部執行，使用DllImport導入的方法必須使用extern修飾符。
MessageBox 則是函數名，擁有4個參數，其返回值為數字。
大多數的API都能傳遞並返回值。
添中Click點擊事件代碼:
protected void button1_Click(object sender, System.EventArgs e)
{
MessageBox (0,"API Message Box","API Demo",0);
}
編譯並運行這個程序，當你點擊按鈕後，你將會看到對話框，這便是你使用的API函數。
使用結構體
操作帶有結構體的API比使用簡單的API要復雜的多。但是一旦你掌握了API的過程，那個整個API世界將在你的掌握之中。
下面的例子中我們將使用GetSystemInfo API 來獲取整個系統的信息。
第一步還是打開C#建立一個Form工程，同樣的添中一個Button按鈕，在代碼窗中輸入下面的代碼，導入Namespace：
using System.Runtime.InteropServices;
聲明一個結構體，它將做為GetSystemInfo的一個參數：
[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;
}
聲明API函數:
[DllImport("kernel32")]
static extern void GetSystemInfo(ref SYSTEM_INFO pSI);
添加下面的代碼至按鈕的點擊事件處理中：
首先創建一個SYSTEM_INFO結構體，並將其傳遞給GetSystemInfo函數。
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結構體，那麼就可以以返回的參數來執行操作了。
e.g.listBox1.InsertItem (0,pSI.dwActiveProcessorMask.ToString());:
//
//
//
}
catch(Exception er)
{
MessageBox.Show (er.Message);
}
}
//Created By Ajit Mungale
//程序補充 飛刀
namespace UsingAPI
{
using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.WinForms;
using System.Data;
using System.Runtime.InteropServices;
//Struct 收集系統信息
[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 收集內存情況
[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;
//獲取系統信息
[DllImport("kernel32")]
static extern void GetSystemInfo(ref SYSTEM_INFO pSI);
//獲取內存信息
[DllImport("kernel32")]
static extern void GlobalMemoryStatus(ref MEMORYSTATUS buf);
//處理器類型
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());
/************** 從 GlobalMemoryStatus 獲取返回值****************/
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 );
}
}
}
}
