关于vb.net里面api Unicode/ANSI调用一个问题解答

本文链接：https://blog.youkuaiyun.com/VirtualDesktop/article/details/1517135

昨天我在codeproject的一篇文章（http://www.codeproject.com/vista/textonglass.asp）收到一个回复（http://www.codeproject.com/vista/textonglass.asp?select=1914299&forumid=336550&df=100&msg=1914299），他遇到的问题如下：

I've converted the DrawGlowingText function from the c# version that was in "GlassText.cs" to Vb.net

Every thing seems to work but the text is drawn using japaneese signs, Not normal letters :0
Can anyone tell me whats wrong?

翻译成中文的大意是：我把GlassText.cs中的DrawGlowingText 函数从C#翻译成了vb.net，但是画出的文本却全是日文（其实是乱码），这是为什么？

下面接着就贴着长长的代码了，大家有兴趣可以去一看。

我把他的代码复制下来，一到vista里面调试，发觉是乱码。于是感觉是他的函数调用方式出了问题，一看，果然。他的DrawThemeTextEx函数声明的时候用的是vb6时代的api声明方式（该函数vista特有）：

Public Declare Function DrawThemeTextEx Lib "UxTheme.dll" (ByVal hTheme As IntPtr, ByVal hdc As IntPtr, ByVal iPartId As Integer, ByVal iStateId As Integer, ByVal text As String, ByVal iCharCount As Integer, ByVal dwFlags As Integer, ByRef pRect As RECT, ByRef pOptions As S_DTTOPTS) As Integer

然而，.net对于这种声明默认被声明的函数为Ansi调用，于是string参数被强制作为Ansi字符串读取。而我们知道，.net里面所有的string默认都是unicode。更不幸的是，DrawThemeTextEx本身就是一个Unicode函数。于是这种种错误加在一起，便造成了乱码。那怎么解决呢？方法很简单：使用.net标准的P/Invoke声明，显式声明该函数为Unicode调用：

< DllImport( " UxTheme.dll " , ExactSpelling: = True , SetLastError: = True , CharSet: = CharSet.Unicode) > _

Shared Function DrawThemeTextEx(ByVal hTheme As IntPtr, ByVal hdc As IntPtr, ByVal iPartId As Integer, ByVal iStateId As Integer, ByVal text As String, ByVal iCharCount As Integer, ByVal dwFlags As Integer, ByRef pRect As RECT, ByRef pOptions As S_DTTOPTS) As Integer

End Function

最后整个vb类代码如下，这个代码的作用是在vista的玻璃区域画出像vista窗体标题栏那样效果的文字，工作函数是DrawGlowingText，是一个静态函数，可以直接调用：

Imports System

Imports System.Drawing

Imports System.Windows.Forms

Imports System.Runtime.InteropServices

Public Class VistaAPI

Public Declare Function DwmIsCompositionEnabled Lib "dwmapi.dll" (ByRef en As Integer) As Integer

Public Declare Function DwmExtendFrameIntoClientArea Lib "dwmapi.dll" (ByVal hWnd As IntPtr, ByRef margins As MARGIN_STRUCT) As Integer

'***************************you have to declare it as an unicode function***************************

<DllImport("UxTheme.dll", ExactSpelling:=True, SetLastError:=True, CharSet:=CharSet.Unicode)> _

End Function

'***************************pass BITMAPINFO byref***************************

Public Declare Function CreateDIBSection Lib "gdi32.dll" (ByVal hdc As IntPtr, ByRef pbmi As BITMAPINFO, ByVal iUsage As UInt32, ByVal ppvBits As Integer, ByVal hSection As IntPtr, ByVal dwOffset As UInt32) As IntPtr

'***************************************************************************

Public Declare Function BitBlt Lib "gdi32.dll" (ByVal hdc As IntPtr, ByVal nXDest As Integer, ByVal nYDest As Integer, ByVal nWidth As Integer, ByVal nHeight As Integer, ByVal hdcSrc As IntPtr, ByVal nXSrc As Integer, ByVal nYSrc As Integer, ByVal dwRop As Int32) As Boolean

Public Declare Function SelectObject Lib "gdi32.dll" (ByVal hDC As IntPtr, ByVal hObject As IntPtr) As IntPtr

Public Declare Function DeleteObject Lib "gdi32.dll" (ByVal hObject As IntPtr) As Boolean

Public Declare Function CreateCompatibleDC Lib "gdi32.dll" (ByVal hDC As IntPtr) As IntPtr

Public Declare Function DeleteDC Lib "gdi32.dll" (ByVal hdc As IntPtr) As Boolean

Public Structure RECT

Public Sub New(ByVal tLeft As Integer, ByVal tTop As Integer, ByVal tRight As Integer, ByVal tBottom As Integer)

Left = tLeft

Top = tTop

Right = tRight

Bottom = tBottom

End Sub

Public Left As Integer

Public Top As Integer

Public Right As Integer

Public Bottom As Integer

End Structure

'****************************************************************************************

Public Structure BITMAPINFOHEADER 'BITMAPINFOHEADER you must declare this

Dim biSize As Integer

Dim biWidth As Integer

Dim biHeight As Integer

Dim biPlanes As Short

Dim biBitCount As Short

Dim biCompression As Integer

Dim biSizeImage As Integer

Dim biXPelsPerMeter As Integer

Dim biYPelsPerMeter As Integer

Dim biClrUsed As Integer

Dim biClrImportant As Integer

End Structure

Public Structure RGBQUAD

Dim rgbBlue As Byte

Dim rgbGreen As Byte

Dim rgbRed As Byte

Dim rgbReserved As Byte

End Structure

Public Structure BITMAPINFO

Dim bmiHeader As BITMAPINFOHEADER

Dim bmiColors As RGBQUAD

End Structure

'************************************************************************************************

Public Structure S_DTTOPTS

Dim dwSize As Integer

Dim dwFlags As Integer

Dim crText As Integer

Dim crBorder As Integer

Dim crShadow As Integer

Dim iTextShadowType As Integer

Dim ptShadowOffset As POINT

Dim iBorderSize As Integer

Dim iFontPropId As Integer

Dim iColorPropId As Integer

Dim iStateId As Integer

Dim fApplyOverlay As Boolean

Dim iGlowSize As Integer

Dim pfnDrawTextCallback As Integer

Dim lParam As IntPtr

End Structure

Private Const DTT_COMPOSITED As Integer = 8192

Private Const DTT_GLOWSIZE As Integer = 2048

Private Const DTT_TEXTCOLOR As Integer = 1

Public Structure POINT

Dim cx, cy As Integer

Sub New(ByVal X As Integer, ByVal Y As Integer)

cx = X

cy = Y

End Sub

End Structure

Public Structure MARGIN_STRUCT

Dim cxLeftWidth, cxRightWidth, cyTopHeight, cyBottomHeight As Integer

Sub New(ByVal Left As Integer, ByVal Right As Integer, ByVal Top As Integer, ByVal Bottom As Integer)

cxLeftWidth = Left

cxRightWidth = Right

cyTopHeight = Top

cyBottomHeight = Bottom

End Sub

End Structure

Public Shared Sub DrawGlowingText(ByVal Graphics As Graphics, ByVal text As String, ByVal fnt As Font, ByVal bounds As Rectangle, ByVal Clr As Color, ByVal flags As TextFormatFlags)

Dim primaryHdc As IntPtr = Graphics.GetHdc

Dim bitmapOld As IntPtr = IntPtr.Zero

Dim hfontOld As IntPtr = IntPtr.Zero

'' Create a memory DC so we can work offscreen

Dim memoryHdc As IntPtr = CreateCompatibleDC(primaryHdc)

'' Create a device-independent bitmap and select it into our DC

Dim info As BITMAPINFO = New BITMAPINFO

'******************it's the size of BITMAPINFOHEADER, not BITMAPINFO ***********************

info.bmiHeader.biSize = Marshal.SizeOf(info.bmiHeader)

'*******************************************************************************************

'******************* the size of glow is 15px,make it larger********************************

Dim textBounds As RECT = New RECT(0, 0, bounds.Right - bounds.Left + 2 * 15, bounds.Bottom - bounds.Top + 2 * 15)

Dim screenBounds As RECT = New RECT(bounds.Left - 15, bounds.Top - 15, bounds.Right + 15, bounds.Bottom + 15)

'******************************************************************************************

info.bmiHeader.biWidth = bounds.Width + 30

info.bmiHeader.biHeight = -bounds.Height - 30

info.bmiHeader.biPlanes = 1

info.bmiHeader.biBitCount = 32

info.bmiHeader.biCompression = 0 '' BI_RGB

Dim dib As IntPtr = CreateDIBSection(primaryHdc, info, 0, 0, IntPtr.Zero, 0)

bitmapOld = SelectObject(memoryHdc, dib)

' Create and select font

Dim fontHandle As IntPtr = fnt.ToHfont

hfontOld = SelectObject(memoryHdc, fontHandle)

'' Draw glowing text

Dim renderer As System.Windows.Forms.VisualStyles.VisualStyleRenderer = New System.Windows.Forms.VisualStyles.VisualStyleRenderer(System.Windows.Forms.VisualStyles.VisualStyleElement.Window.Caption.Active)

Dim dttOpts As S_DTTOPTS = New S_DTTOPTS

'********************** GetType is no needed **********************

dttOpts.dwSize = Marshal.SizeOf(dttOpts)

'******************************************************************

dttOpts.dwFlags = DTT_COMPOSITED Or DTT_GLOWSIZE Or DTT_TEXTCOLOR

dttOpts.crText = ColorTranslator.ToWin32(Clr)

dttOpts.iGlowSize = 15 '' This is about the size Microsoft Word 2007 uses(15)

DrawThemeTextEx(renderer.Handle, memoryHdc, 0, 0, text, -1, flags, textBounds, dttOpts)

'DrawThemeTextEx(renderer.Handle, memoryHdc, 0, 0, text, -1, (int)flags, ref textBounds, ref dttOpts);

'' Copy to foreground

Dim SRCCOPY As Integer = &HCC0020 ' old C# Value was: 0x00CC0020

BitBlt(primaryHdc, screenBounds.Left, screenBounds.Top, _