Problem using SendMessage in C# to get values of a ListBox on other application

[Christian Berczely]

I am using C# to build an application that gets values of a ListBox
that is in another application.

Here, hListBox is the handle to the ListBox running in the other
application.

I am using SendMessage(hListBox, LB_GETCURSEL, IntPtr.Zero,
IntPtr.Zero) to get the current selected item from this ListBox. This
works well.


Then when I try to get the length and text it does not work.

This is what I have used to get the text: SendMessage(hListBox,
LB_GETTEXT, new IntPtr(pos), ipRemoteBuffer);

Do I need also to call VirtualAllocEx to create a text buffer on the
other application's space?
Then use ReadProcessMemory to read this out?



I have created a .net VC application that has the ListBox within the
same app where by code is, and this works. So I think the issue is on
getting the text from an external application...

I would really appreciate some sample code.
Christian

[Peter Duniho]

Post by Christian Berczely
I am using C# to build an application that gets values of a ListBox
that is in another application.
Here, hListBox is the handle to the ListBox running in the other
application.
I am using SendMessage(hListBox, LB_GETCURSEL, IntPtr.Zero,
IntPtr.Zero) to get the current selected item from this ListBox. This
works well.
Then when I try to get the length and text it does not work.

"Does not work" is a pretty vague problem statement.

Post by Christian Berczely
This is what I have used to get the text: SendMessage(hListBox,
LB_GETTEXT, new IntPtr(pos), ipRemoteBuffer);
Do I need also to call VirtualAllocEx to create a text buffer on the
other application's space?
Then use ReadProcessMemory to read this out?

Windows will marshal WM_GETTEXT for you. I don't know about LB_GETTEXT.
It's possible you need to allocate shared memory the other process can
write and which you can read. I have also read that if the ListBox has
the LBS_HASSTRINGS style, it should work and otherwise it won't (and
that is probably true regardless of cross-process or not).

It's also possible your p/invoke declaration is incorrect. .NET will
have to marshal any string declared in the p/invoke method. If you are
instead passing an IntPtr, then you have to make sure you know how to
interpret it.

Without a proper concise-but-complete code example, that's about as
specific as I can offer in the way of comments.

Pete

[Christian Berczely]

Here is the code:

public const int LB_GETTEXT = 0x0189;
public const int LB_GETTEXTLEN = 0x018A;
public const int LB_GETCURSEL = 0x0188;
public const int LB_GETCOUNT = 0x018B;

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError =
false)]
private static extern IntPtr SendMessage(IntPtr hWnd, int Msg, IntPtr
wParam, IntPtr lParam);

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError =
false)]
private static extern IntPtr SendMessage(IntPtr hWnd, int Msg, IntPtr
wParam, [MarshalAs(UnmanagedType.LPTStr)] StringBuilder lParam);

private void test(IntPtr hwnd_listbox)
{
// hwnd_listbox is from a ListBox that is in another application

int count = (int)SendMessage(hwnd_listbox, LB_GETCOUNT,
IntPtr.Zero, IntPtr.Zero); // this works, so hwnd_listbox is correct

int pos = (int)SendMessage(hwnd_listbox, LB_GETCURSEL,
IntPtr.Zero, IntPtr.Zero); // this works

int len = (int)SendMessage(hwnd_listbox, LB_GETTEXTLEN,
(IntPtr)pos, IntPtr.Zero); // wrong: returns 4

StringBuilder sbTxt = new StringBuilder(len + 1);
SendMessage(hwnd_listbox, LB_GETTEXT, (IntPtr)pos, sbTxt); //
wrong: returns garbage

string text = sbTxt.ToString();
}



What could be wrong?

[Peter Duniho]

Post by Christian Berczely
[...]
What could be wrong?

Any number of things, including but not limited to the things I already
mentioned in my previous reply.

[b***@gmail.com]

SendMessage to check checkbox in listview can you help me out