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);
    }
}

//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);
            }
        }
    }
}