C#--API

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); 
                
            } 
            
        } 
        
    } 
    
}

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