Interop: Using WriteProcessMemory on LVITEM Structure

[Charles Law]

I have defined LVITEM as follows:

<StructLayout(LayoutKind.Sequential)> Private Structure LVITEM
Dim mask As Int16
Dim iItem As Int16
Dim iSubItem As Int16
Dim state As Int16
Dim stateMask As Int16
<MarshalAs(UnmanagedType.LPWStr)> Dim pszText As IntPtr
Dim cchTextMax As Int16
Dim iImage As Int16
Dim lParam As Integer
Dim iIndent As Int16
End Structure

When I execute the following code I get an exception on the last line:

<code>
Dim lvi As LVITEM

''dwSize = Marshal.SizeOf(lvi) ' This does not work either
dwSize = 24

Dim SysShared As IntPtr
Dim StringMemory As IntPtr

lvi.mask = LVIF_TEXT
lvi.cchTextMax = 100
lvi.iSubItem = 0

SysShared = GetMemSharedNT(lPID, dwSize, hProcess)
StringMemory = GetMemSharedNT(lPID, 100, hProcess)

lvi.pszText = StringMemory

WriteProcessMemory(hProcess, SysShared, lvi, dwSize,
BytesWritten)
</code>

The error I get is

"Can not marshal field pszText of type LVITEM: Invalid managed/unmanaged
type combination (Int/UInt must be paired with I or U)."

I guess that pszText should be defined 'As String', but then I have a
problem making it point to the memory I have allocated.

Does anyone have any idea how to get round this? I have a sample in C from
this site

http://www.codeproject.com/threads/int64_memsteal.asp

but I would really prefer to do the whole thing in VB.NET.

TIA

Charles

[Dragon]

Hi Charles,

If you want to make pszText an IntPtr, you don't need MarshalAsAttribute
at all. If it was a String then yes, you need a marshalling attribute to
specify whether it is a LPStr, LPWStr, LPTStr or a ByValTStr. IntPtr can
be passed only as 4-byte integer, thus it don't need any marshalling
attribute.

BTW, your LVITEM declaration is wrong. All fields there are Int32's, not
Int16's.

HTH
Roman

"Charles Law" <bl***@nowhere.com> ñîîáùèë/ñîîáùèëà â íîâîñòÿõ ñëåäóþùåå:
news:Oy**************@TK2MSFTNGP09.phx.gbl...

I have defined LVITEM as follows:

<StructLayout(LayoutKind.Sequential)> Private Structure LVITEM
Dim mask As Int16
Dim iItem As Int16
Dim iSubItem As Int16
Dim state As Int16
Dim stateMask As Int16
<MarshalAs(UnmanagedType.LPWStr)> Dim pszText As IntPtr
Dim cchTextMax As Int16
Dim iImage As Int16
Dim lParam As Integer
Dim iIndent As Int16
End Structure

When I execute the following code I get an exception on the last line:

<code>
Dim lvi As LVITEM

''dwSize = Marshal.SizeOf(lvi) ' This does not work either
dwSize = 24

Dim SysShared As IntPtr
Dim StringMemory As IntPtr

lvi.mask = LVIF_TEXT
lvi.cchTextMax = 100
lvi.iSubItem = 0

SysShared = GetMemSharedNT(lPID, dwSize, hProcess)
StringMemory = GetMemSharedNT(lPID, 100, hProcess)

lvi.pszText = StringMemory

WriteProcessMemory(hProcess, SysShared, lvi, dwSize,
BytesWritten)
</code>

The error I get is

"Can not marshal field pszText of type LVITEM: Invalid managed/unmanaged type combination (Int/UInt must be paired with I or U)."

I guess that pszText should be defined 'As String', but then I have a
problem making it point to the memory I have allocated.

Does anyone have any idea how to get round this? I have a sample in C from this site

http://www.codeproject.com/threads/int64_memsteal.asp

but I would really prefer to do the whole thing in VB.NET.

TIA

Charles

[Charles Law]

Hi Roman

Thanks. I removed the MarshalAs attribute from the IntPtr and I no longer
get the exception.

I took the following LVITEM definition from the MSDN

<extract>
typedef struct _LVITEM {
UINT mask;
int iItem;
int iSubItem;
UINT state;
UINT stateMask;
LPTSTR pszText;
int cchTextMax;
int iImage;
LPARAM lParam;
#if (_WIN32_IE >= 0x0300)
int iIndent;
#endif
#if (_WIN32_IE >= 0x560)
int iGroupId;
UINT cColumns; // tile view columns
PUINT puColumns;
#endif
} LVITEM, *LPLVITEM;
</extract>

and duly converted the elements to .NET types, so doesn't that mean that an
int should be translated to int16 in .NET? With the exception that I
mentioned in the OP, this definition works for me, although I admit that it
also works using int32s.

Charles
"Dragon" <[e-mail]> wrote in message
news:uu****************@tk2msftngp13.phx.gbl...

Hi Charles,

If you want to make pszText an IntPtr, you don't need MarshalAsAttribute
at all. If it was a String then yes, you need a marshalling attribute to
specify whether it is a LPStr, LPWStr, LPTStr or a ByValTStr. IntPtr can
be passed only as 4-byte integer, thus it don't need any marshalling
attribute.

BTW, your LVITEM declaration is wrong. All fields there are Int32's, not
Int16's.

HTH
Roman

"Charles Law" <bl***@nowhere.com> ñîîáùèë/ñîîáùèëà â íîâîñòÿõ ñëåäóþùåå:
news:Oy**************@TK2MSFTNGP09.phx.gbl...

I have defined LVITEM as follows:

<StructLayout(LayoutKind.Sequential)> Private Structure LVITEM
Dim mask As Int16
Dim iItem As Int16
Dim iSubItem As Int16
Dim state As Int16
Dim stateMask As Int16
<MarshalAs(UnmanagedType.LPWStr)> Dim pszText As IntPtr
Dim cchTextMax As Int16
Dim iImage As Int16
Dim lParam As Integer
Dim iIndent As Int16
End Structure

When I execute the following code I get an exception on the last line:

<code>
Dim lvi As LVITEM

''dwSize = Marshal.SizeOf(lvi) ' This does not work either
dwSize = 24

Dim SysShared As IntPtr
Dim StringMemory As IntPtr

lvi.mask = LVIF_TEXT
lvi.cchTextMax = 100
lvi.iSubItem = 0

SysShared = GetMemSharedNT(lPID, dwSize, hProcess)
StringMemory = GetMemSharedNT(lPID, 100, hProcess)

lvi.pszText = StringMemory

WriteProcessMemory(hProcess, SysShared, lvi, dwSize,
BytesWritten)
</code>

The error I get is

"Can not marshal field pszText of type LVITEM: Invalid

managed/unmanaged

type combination (Int/UInt must be paired with I or U)."

I guess that pszText should be defined 'As String', but then I have a
problem making it point to the memory I have allocated.

Does anyone have any idea how to get round this? I have a sample in C

from

this site

http://www.codeproject.com/threads/int64_memsteal.asp

but I would really prefer to do the whole thing in VB.NET.

TIA

Charles

[Dragon]

> and duly converted the elements to .NET types, so doesn't that mean
that an

int should be translated to int16 in .NET?

int (as well as UINT) is 4-byte integer, so it's .NET equivalent is
Int32 (Well it's actually UInt32 for UINT, but using UInt's in VB 2002/3
is a real pain).
Int16 is for short datatype.