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使用C#封装Win32API

微软.NET框架的类库功能强大，内容丰富，可以处理大部分的编程要求，但在一些场合下，.NET框架类库不提供支持，此时需要借助Win32API来实现了。

一般的小弟不推荐在.NET程序中使用Win32API,因为这样不符合.NET编程的安全框架，而且让程序绑定到特定的操作系统，因为未来你的.NET程序可能不在Win32操作系统下运行。

推荐归推荐，有时候要用还得用，在此说说.NET下使用Win32API，本人现在使用C#,因此在此只说说C#语言来使用Win32API。

在C#使用Win32API很方便，只需要从指定的DLL文件中导入函数声明即可。比如在某个类中写下
[System.Runtime.InteropServices.DllImport(“gdi32.dll”)]
public static extern int GetDeviceCaps(int hDC , int index );
此后程序就像调用静态函数一样调用这个API函数了。这有点类似VB中声明API了。

大家知道，Win32API是平面结构，将一个DLL中的API罗列出来，成百上千的API一字排开，好生壮观，可惜使用不方便，调用它们需要了解各个API入口和出口以及各个API之间的影响，而且一些API比较危险，需要小心调用，若在错误的时间使用错误的参数调用错误的API则可能导致系统资源泄漏，程序突然退出，甚至会伤害操作系统。

而.NET类库则是树状的立体结构，它使用了面向对象的编程结构，从而掩盖了很多细节，我们调用也方便，也很安全。

以前小弟为了调用API就是在到用的时候就声明API，或者作个模块，列出很多API声明供其他地方调用。经验告诉我，这种简单的用法不够好。于是小弟就开始使用C#的语法结构来封装API。

在此使用API函数GetDeviceCaps作例子，这个函数就是获得指定设备上下文的某些信息，参数为设备上下文句柄(hdc)和类型为DeviceCapsConst信息编号。这个设备上下文句柄是个比较重的句柄，严禁浪费，用完只后需要释放掉该句柄，但释放HDC并不简单，需要知道句柄的来源，当使用CreateDC获得的句柄则必须使用DeleteDC来释放。

对于比较重要的资源，比如句柄，文件，数据库连接等等，有个原则就是尽晚获得，尽早释放，因此需要尽量减少持有句柄的时间。

小弟定义了一个类DeviceCapsClass,用于封装GetDeviceCaps,在获得一个句柄时就立即多次调用GetDeviceCaps来获得所有的信息，然后保存到一个缓冲区中，然后立即释放句柄。并定义了方便的访问缓冲数据的接口。这样其他程序只需要实例化一个DeviceCapsClass，调用它的属性就可获得设备上下文信息而无需考虑细节。

其实这种做法.NET框架类库自己就这么搞，大家看看.NET类库的反编译结果，可以看到.NET类库中有很多就是Win32API的封装。相信大家已经这么做了或将来也这样做。
现列出DeviceCapsClass所有代码

——————————————————————————–

using System;
namespace Windows32
{
///

/// 获得指定设备上下文信息的对象,本模块为API函数GetDeviceCaps的封装
///

/// 编制有为青年 XDesigner 2006-5-4
public class DeviceCapsClass
{
#region 静态成员 **************************************************************************

private static DeviceCapsClass myDisplayInstance = null;
///

/// 针对屏幕的设备上下文信息对象
///

/// 程序可能经常访问屏幕的设备上下文信息，在此专门提供静态成员给予访问
public static DeviceCapsClass DispalyInstance
{
get
{
if( myDisplayInstance == null)
{
myDisplayInstance = new DeviceCapsClass();
myDisplayInstance.ResetForDisplay();
}
return myDisplayInstance ;
}
}

#endregion

#region 构造函数 **************************************************************************

///

/// 无作为的初始化对象
///

public DeviceCapsClass()
{
}
///

/// 使用指定设备上下文初始化对象
///

/// 设备上下文句柄 public DeviceCapsClass( int hdc )
{
Reset( hdc );
}
///

/// 使用指定设备名初始化对象
///

/// 本函数根据名称创建设备上下文,获得所需数据后立即删除设备上下文
/// 设备名 public DeviceCapsClass( string vDriverName )
{
Reset( vDriverName );
}

#endregion

private string strDriverName = null;
///

/// 设备名称
///

public string DriverName
{
get{ return strDriverName ;}
}
public void Reset( int hDC )
{
strDriverName = null;
System.Array myValues = System.Enum.GetValues( typeof( enumDeviceCapsConst ));
intValues = new int[ myValues.Length * 2 ];
for(int iCount = 0 ; iCount < myValues.Length ; iCount ++ ) { int CapsValue = Convert.ToInt32( myValues.GetValue( iCount )); intValues[iCount * 2 ] = CapsValue ; intValues[iCount * 2 + 1] = GetDeviceCaps( hDC , CapsValue ); } } public void Reset( string vDriverName ) { int hdc = CreateDC( vDriverName , null , 0 , 0 ); if( hdc != 0 ) { Reset( hdc ); DeleteDC( hdc ); strDriverName = vDriverName ; } } public void ResetForDisplay( ) { Reset( "DISPLAY" ); } ///

/// 已重载:获得对象所有内容的字符串
///
///
public override string ToString()
{
if( intValues == null)
return “DeviceCapsClass:对象尚未初始化”;
System.Text.StringBuilder myStr = new System.Text.StringBuilder();
myStr.Append(“DeviceCapsClass”);
if( strDriverName != null)
myStr.Append(” Driver:” + strDriverName );
System.Array myValues = System.Enum.GetValues( typeof( enumDeviceCapsConst ));
foreach( enumDeviceCapsConst dc in myValues )
{
myStr.Append( System.Environment.NewLine );
myStr.Append( dc.ToString() + ” = ” + GetValue( dc ) );
}
return myStr.ToString();
}

#region 获得数据的属性群 ******************************************************************

///

/// Device driver version
///

public int DRIVERVERSION{ get { return GetValue( enumDeviceCapsConst.DRIVERVERSION );} }
///

/// Device classification
///

public int TECHNOLOGY { get { return GetValue( enumDeviceCapsConst.TECHNOLOGY );} }
///

/// Horizontal size in millimeters
///

public int HORZSIZE { get { return GetValue( enumDeviceCapsConst.HORZSIZE );} }
///

/// Vertical size in millimeters
///

public int VERTSIZE { get { return GetValue( enumDeviceCapsConst.VERTSIZE );} }
///

/// Horizontal width in pixels
///

public int HORZRES { get { return GetValue( enumDeviceCapsConst.HORZRES );} }
///

/// Vertical width in pixels
///

public int VERTRES { get { return GetValue( enumDeviceCapsConst.VERTRES );} }
///

/// Logical pixels/inch in X
///

public int LOGPIXELSX { get { return GetValue( enumDeviceCapsConst.LOGPIXELSX );} }
///

/// Logical pixels/inch in Y
///

public int LOGPIXELSY { get { return GetValue( enumDeviceCapsConst.LOGPIXELSY );} }
///

/// Number of planes
///

public int PLANES { get { return GetValue( enumDeviceCapsConst.PLANES );} }
///

/// Number of brushes the device has
///

public int NUMBRUSHES { get { return GetValue( enumDeviceCapsConst.NUMBRUSHES );} }
///

/// Number of colors the device supports
///

public int NUMCOLORS { get { return GetValue( enumDeviceCapsConst.NUMCOLORS );} }
///

/// Number of fonts the device has
///

public int NUMFONTS { get { return GetValue( enumDeviceCapsConst.NUMFONTS );} }
///

/// Number of pens the device has
///

public int NUMPENS { get { return GetValue( enumDeviceCapsConst.NUMPENS );} }
///

/// Length of the X leg
///

public int ASPECTX { get { return GetValue( enumDeviceCapsConst.ASPECTX );} }
///

/// Length of the hypotenuse
///

public int ASPECTXY { get { return GetValue( enumDeviceCapsConst.ASPECTXY );} }
///

/// Length of the Y leg
///

public int ASPECTY { get { return GetValue( enumDeviceCapsConst.ASPECTY );} }
///

/// Size required for device descriptor
///

public int PDEVICESIZE { get { return GetValue( enumDeviceCapsConst.PDEVICESIZE );} }
///

/// Clipping capabilities
///

public int CLIPCAPS { get { return GetValue( enumDeviceCapsConst.CLIPCAPS );} }
///

/// Number of entries in physical palette
///

public int SIZEPALETTE { get { return GetValue( enumDeviceCapsConst.SIZEPALETTE );} }
///

/// Number of reserved entries in palette
///

public int NUMRESERVED { get { return GetValue( enumDeviceCapsConst.NUMRESERVED );} }
///

/// Actual color resolution
///

public int COLORRES { get { return GetValue( enumDeviceCapsConst.COLORRES );} }
///

/// Physical Printable Area x margin
///

public int PHYSICALOFFSETX { get { return GetValue( enumDeviceCapsConst.PHYSICALOFFSETX );} }
///

/// Physical Printable Area y margin
///

public int PHYSICALOFFSETY { get { return GetValue( enumDeviceCapsConst.PHYSICALOFFSETY );} }
///

/// Physical Height in device units
///

public int PHYSICALHEIGHT{ get { return GetValue( enumDeviceCapsConst.PHYSICALHEIGHT );} }
///

/// Physical Width in device units
///

public int PHYSICALWIDTH { get { return GetValue( enumDeviceCapsConst.PHYSICALWIDTH );} }
///

/// Scaling factor x
///

public int SCALINGFACTORX { get { return GetValue( enumDeviceCapsConst.SCALINGFACTORX );} }
///

/// Scaling factor y
///

public int SCALINGFACTORY { get { return GetValue( enumDeviceCapsConst.SCALINGFACTORY );} }
public int LISTEN_OUTSTANDING{ get { return GetValue( enumDeviceCapsConst.LISTEN_OUTSTANDING );} }
///

/// Curve capabilities
///

public int CURVECAPS{ get { return GetValue( enumDeviceCapsConst.CURVECAPS );} }
///

/// Line capabilities
///

public int LINECAPS{ get { return GetValue( enumDeviceCapsConst.LINECAPS );} }
///

/// Polygonal capabilities
///

public int POLYGONALCAPS { get { return GetValue( enumDeviceCapsConst.POLYGONALCAPS );} }
///

/// Text capabilities
///

public int TEXTCAPS { get { return GetValue( enumDeviceCapsConst.TEXTCAPS );} }

#endregion

#region 声明 Win32 API 函数及常量 *********************************************************

[System.Runtime.InteropServices.DllImport(“gdi32.dll”, CharSet=System.Runtime.InteropServices.CharSet.Auto)]
private static extern int GetDeviceCaps(int hDC , int index );

[System.Runtime.InteropServices.DllImport(“User32.dll”, CharSet=System.Runtime.InteropServices.CharSet.Auto)]
private static extern int ReleaseDC(int hWnd, int hDC);

[System.Runtime.InteropServices.DllImport(“gdi32.dll”, CharSet=System.Runtime.InteropServices.CharSet.Auto)]
private static extern int CreateDC( string strDriver , string strDevice , int Output , int InitData );

[System.Runtime.InteropServices.DllImport(“gdi32.dll”, CharSet=System.Runtime.InteropServices.CharSet.Auto)]
private static extern int DeleteDC( int Hdc );

///

/// 为Win32API函数GetDeviceCaps的第二个参数配备的枚举变量
///

private enum enumDeviceCapsConst
{
///

/// Device driver version
///

DRIVERVERSION = 0 ,
///

/// Device classification
///

TECHNOLOGY = 2 ,
///

/// Horizontal size in millimeters
///

HORZSIZE = 4 ,
///

/// Vertical size in millimeters
///

VERTSIZE = 6 ,
///

/// Horizontal width in pixels
///

HORZRES = 8 ,
///

/// Vertical width in pixels
///

VERTRES = 10 ,
///

/// Logical pixels/inch in X
///

LOGPIXELSX = 88 ,
///

/// Logical pixels/inch in Y
///

LOGPIXELSY = 90 ,
///

/// Number of planes
///

PLANES = 14 ,
///

/// Number of brushes the device has
///

NUMBRUSHES = 16 ,
///

/// Number of colors the device supports
///

NUMCOLORS = 24 ,
///

/// Number of fonts the device has
///

NUMFONTS = 22 ,
///

/// Number of pens the device has
///

NUMPENS = 18 ,
///

/// Length of the X leg
///

ASPECTX = 40 ,
///

/// Length of the hypotenuse
///

ASPECTXY = 44 ,
///

/// Length of the Y leg
///

ASPECTY = 42 ,
///

/// Size required for device descriptor
///

PDEVICESIZE = 26 ,
///

/// Clipping capabilities
///

CLIPCAPS = 36 ,
///

/// Number of entries in physical palette
///

SIZEPALETTE = 104 ,
///

/// Number of reserved entries in palette
///

NUMRESERVED = 106 ,
///

/// Actual color resolution
///

COLORRES = 108 ,
///

/// Physical Printable Area x margin
///

PHYSICALOFFSETX = 112 ,
///

/// Physical Printable Area y margin
///

PHYSICALOFFSETY = 113 ,
///

/// Physical Height in device units
///

PHYSICALHEIGHT = 111 ,
///

/// Physical Width in device units
///

PHYSICALWIDTH = 110 ,
///

/// Scaling factor x
///

SCALINGFACTORX = 114 ,
///

/// Scaling factor y
///

SCALINGFACTORY = 115 ,
LISTEN_OUTSTANDING = 1 ,
///

/// Curve capabilities
///

CURVECAPS = 28 ,
///

/// Line capabilities
///

LINECAPS = 30 ,
///

/// Polygonal capabilities
///

POLYGONALCAPS = 32 ,
///

/// Text capabilities
///

TEXTCAPS = 34 ,
}

#endregion

#region 内部私有成员 **********************************************************************

private int[] intValues = null;

private int GetValue( enumDeviceCapsConst CapsValue)
{
if( intValues == null)
return int.MinValue ;
for(int iCount = 0 ; iCount < intValues.Length ; iCount += 2 ) { if( intValues[iCount] == Convert.ToInt32( CapsValue) ) return intValues[iCount+1]; } return int.MinValue ; } #endregion }//public class DeviceCapsClass }

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