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: Selenium WebDriver

  [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 );

       }

   }

  }

}