C#中调用API

介绍 
API( Application Programming Interface ),我想大家不会陌生,它是我们Windows编程的常客,虽然基于.Net平台的C#有了强大的类库,但是,我们还是不能否认API在Windows编程中的重要性.大多数的编程语言都支持API编程,而.Net平台中的MFC(Microsoft Foundation Class Library)构架本身就封装了大部分的API.

做为程序员,我们需要了解API从字面上了解便是编程接口,因此,做为开发者,需要了解的只是API的使用方法.

API根据操作系统、处理器及功能性的不同而拥有很多不同的类型.     操作系统特用的API:

每种操作系统都有许多通用的API以及一些特用的API,这些特用的API只能在当前操作系统中执行.

例如：

Windows NT 支持 MS-DOS, Win16, Win32, POSIX ( Portable Operating System Interface ), OS/2 console API; 而 Windows 95 支持 MS-DOS, Win16 以及 Win32 APIs.

Win16 & Win32 API:

Win16是为十六位处理器开发的,早期的操作系统均支持.

Win32则是为32位处理器开发.它可移植性强,被大部分的处理器所支持.

Win32 API在库名后有一个”32”后缀.比如KERNEL32,USER32等.

所有API在下面3个库中得以运行：

Kernel 
User 
GDI

1. KERNEL

他的库名为 KERNEL32.DLL, 他主要用于产生与操作系统之间的关联：

程序加载 
     上下文选择. 
     文件输入输出. 
     内存管理. 
     例如： GlobalMemoryStatus 函数就包括当前物理内存及虚拟内存的使用信息.

2. USER

这个类库在Win32中名叫 USER32.DLL.

它允许管理全部的用户接口,比如：

窗口 
     菜单 
     对话框 
     图标等., 
     例如： DrawIcon 函数将在指定的设备关联上“画”出图标或者鼠标.

3. GDI ( Graphical Device Interface )

它在Win32中的库名为：GDI32.dll,它是图形输出库.使用GDI Windows“画”出窗口、菜单以及对话框等：

它能创建图形输出. 
     它也能保存图形文件. 
     例如： CreateBitmap 函数就能通过指定的长、宽、颜色创建一个位图.
C# 中操作API :

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 ); 
        
    } 
    
}

调用API全部代码

//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); 
                
            } 
            
        } 
        
    } 
    
}