作爲一名C#的初學者來說，使用API確是一件很頭疼的問題。在使用API之間你必須知道如何在C#中使用結構、類型轉換、安全/不安全代碼，可控/不可控代碼等許多知識。
一切從簡單開始，複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：
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using System.Runtime.InteropServices; |
接着添加下面的代碼來聲明一個API：
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[DllImport("User32.dll")] |
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，其返回值爲數字。
大多數的API都能傳遞並返回值。
添中Click點擊事件代碼:
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protected void button1_Click(object sender, System.EventArgs e) |
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要複雜的多。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GetSystemInfoAPI 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：
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using System.Runtime.InteropServices; |
聲明一個結構體，它將做爲GetSystemInfo的一個參數：
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聲明API函數:
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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。
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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。
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//CreatedBy Ajit Mungale
//程序補充 飛刀
namespaceUsingAPI
{
usingSystem;
usingSystem.Drawing;
usingSystem.Collections;
usingSystem.ComponentModel;
usingSystem.WinForms;
usingSystem.Data;
usingSystem.Runtime.InteropServices;
//Struct 收集系統信息
[StructLayout(LayoutKind.Sequential)]
publicstruct SYSTEM_INFO {
publicuint dwOemId;
publicuint dwPageSize;
publicuint lpMinimumApplicationAddress;
publicuint lpMaximumApplicationAddress;
public uintdwActiveProcessorMask;
publicuint dwNumberOfProcessors;
publicuint dwProcessorType;
publicuint dwAllocationGranularity;
publicuint dwProcessorLevel;
publicuint dwProcessorRevision;
}
//struct 收集內存情況
[StructLayout(LayoutKind.Sequential)]
publicstruct MEMORYSTATUS
{
publicuint dwLength;
publicuint dwMemoryLoad;
publicuint dwTotalPhys;
publicuint dwAvailPhys;
publicuint dwTotalPageFile;
publicuint dwAvailPageFile;
publicuint dwTotalVirtual;
publicuint dwAvailVirtual;
}
publicclass Form1 : System.WinForms.Form
{
privateSystem.ComponentModel.Container components;
privateSystem.WinForms.MenuItem menuAbout;
privateSystem.WinForms.MainMenu mainMenu1;
privateSystem.WinForms.ListBox listBox1;
privateSystem.WinForms.Button button1;
//獲取系統信息
[DllImport("kernel32")]
staticextern void GetSystemInfo(ref SYSTEM_INFO pSI);
//獲取內存信息
[DllImport("kernel32")]
staticextern void GlobalMemoryStatus(ref MEMORYSTATUS buf);
//處理器類型
publicconst int PROCESSOR_INTEL_386 = 386;
publicconst int PROCESSOR_INTEL_486 = 486;
publicconst int PROCESSOR_INTEL_PENTIUM = 586;
publicconst int PROCESSOR_MIPS_R4000 = 4000;
publicconst int PROCESSOR_ALPHA_21064 = 21064;
publicForm1()
{
InitializeComponent();
}
publicoverride void Dispose()
{
base.Dispose();
components.Dispose();
}
privatevoid 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);
}
protectedvoid menuAbout_Click (object sender, System.EventArgs e)
{
Formabt=new about() ;
abt.ShowDialog();
}
protectedvoid button1_Click (object sender, System.EventArgs e)
{
try
{
SYSTEM_INFOpSI = new SYSTEM_INFO();
GetSystemInfo(refpSI);
stringCPUType;
switch(pSI.dwProcessorType)
{
casePROCESSOR_INTEL_386 :
CPUType="Intel 386";
break;
casePROCESSOR_INTEL_486 :
CPUType ="Intel 486" ;
break;
casePROCESSOR_INTEL_PENTIUM :
CPUType ="Intel Pentium";
break;
casePROCESSOR_MIPS_R4000 :
CPUType ="MIPS R4000";
break;
casePROCESSOR_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****************/
MEMORYSTATUSmemSt = new MEMORYSTATUS ();
GlobalMemoryStatus(ref memSt);
listBox1.InsertItem(10,"AvailablePage File :"+ (memSt.dwAvailPageFile/1024).ToString ());
listBox1.InsertItem(11,"AvailablePhysical Memory : " + (memSt.dwAvailPhys/1024).ToString());
listBox1.InsertItem(12,"AvailableVirtual Memory:" + (memSt.dwAvailVirtual/1024).ToString ());
listBox1.InsertItem(13,"Sizeof structur :" + memSt.dwLength.ToString());
listBox1.InsertItem(14,"MemoryIn Use :"+ memSt.dwMemoryLoad.ToString());
listBox1.InsertItem(15,"TotalPage Size :"+ (memSt.dwTotalPageFile/1024).ToString ());
listBox1.InsertItem(16,"TotalPhysical Memory :" + (memSt.dwTotalPhys/1024).ToString());
listBox1.InsertItem(17,"TotalVirtual Memory :" + (memSt.dwTotalVirtual/1024).ToString ());
}
catch(Exceptioner)
{
MessageBox.Show(er.Message);
}
}
publicstatic void Main(string[] args)
{
try
{
Application.Run(newForm1());
}
catch(Exceptioner)
{
MessageBox.Show(er.Message );
}
}
}
}
以上代碼僅供參考，未經允許不得轉載。