微软.net精简框架常见问题及回答(中文版)(21)
Dim test(4) As Byte
Dim hObject As GCHandle = GCHandle.Alloc(test, GCHandleType.Pinned)
Dim pObject As IntPtr = hObject.AddrOfPinnedObject()
If hObject.IsAllocated Then
hObject.Free()
End If
最后，可以使用LocalAlloc和Marshalling函数复制内存块得到数据块。
//C#
[DllImport("coredll.dll",SetLastError=true)]
public static extern IntPtr LocalAlloc(uint uFlags, uint uBytes);
[DllImport("coredll.dll",SetLastError=true)]
public static extern IntPtr LocalFree(IntPtr hMem);
[DllImport("coredll.dll",SetLastError=true)]
public static extern IntPtr LocalReAlloc(IntPtr hMem, uint uBytes, uint fuFlags);
public const uint LMEM_FIXED = 0;
public const uint LMEM_MOVEABLE = 2;
public const uint LMEM_ZEROINIT = 0x0040;
byte[] test = new byte[5];
IntPtr p = LocalAlloc(LMEM_FIXED | LMEM_ZEROINIT, (uint)test.Length);
if (p == IntPtr.Zero)
{
throw new OutOfMemoryException();
}
else
{
Marshal.Copy(test, 0, p, test.Length);
}
'VB
<DllImport("coredll.dll", SetLastError:=True)> _
Public Shared Function LocalAlloc(ByVal uFlags As UInt32, ByVal uBytes As UInt32) As IntPtr
End Function
<DllImport("coredll.dll", SetLastError:=True)> _
Public Shared Function LocalFree(ByVal hMem As IntPtr) As IntPtr
End Function
<DllImport("coredll.dll", SetLastError:=True)> _
Public Shared Function LocalReAlloc(ByVal hMem As IntPtr, ByVal uBytes As UInt32, ByVal fuFlags As UInt32) As IntPtr
End Function
Public Const LMEM_FIXED As Integer = 0
Public Const LMEM_MOVEABLE As Integer = 2
Public Const LMEM_ZEROINIT As Integer = &H40
Dim test(4) As Byte
Dim p As IntPtr = LocalAlloc(Convert.ToUInt32(LMEM_FIXED Or LMEM_ZEROINIT), Convert.ToUInt32(test.Length))
If p.Equals(IntPtr.Zero) Then
Throw New OutOfMemoryException
Else
Marshal.Copy(test, 0, p, test.Length)
End If
6.15. Why do I get a MissingMethodException when I call a function from a native DLL?
There are several issues to consider when determining the case of a MissingMethodException. When this exception occurs you should verify the following:
If targeting Pocket PC 2003 use Microsoft eMbedded Visual C++ 4.0.
If targeting Pocket PC 2000 or 2002 use Microsoft eMbedded Visual Tools 3.0
Verify that the parameters to the function match those of the original
A long in native code is typically 32-bits, whereas in the .NET Compact Framework it is 64-bits
Beware of bool
According to MSDN documentation, "Its size is unspecified.":
In a Microsoft specific section of the MSDN documentation, the bool size is described as varying depending on the version of Visual C++ used to build the binary.:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dv_vccelng4/html/ellrfbool.asp
A BOOL is defined as an int (32-bit value)
.NET Compact Framework Blittable Types:
Non Blittable Types and Marshaling Support:
http://msdn.microsoft.com/library/en-us/dv_evtuv/html/etconNonBlittableTypesMarshalingSupport.asp
Make sure that the function name is spelled correctly
Verify that the DLL is located correctly - Windows or executing folder of target device
Verify with DUMPBIN that the names of the functions were not mangled on exporting of the DLL (extern "C" fixes this). More information on this topic can be found in section "6.1. How do I call a function that is in a native DLL?" of this FAQ.