can c# have object* ? - C# Discussion Boards

Re: owner draw of listview and treeview

26-Nov-02 5:29

Absolutely without - I don't know, but to be honest: I don't believe it (at least if even SendMessage is included into the restriction list). However, did you already had a look into the UtilityLibrary from Carlos Perez?? (just search here in CP)It's not only an excellent tutorial, it even has samples for Listbox- and Treeview implementation.
May be this gives you the ultimative hint?? Or you find a way to re-implement the rare API calls into pure C#?
Wish you success! Bye
Matze

Stephane Rodriguez.26-Nov-02 5:36

Stephane Rodriguez.

26-Nov-02 5:36

One word : WndProc

can c# have object* ?

Anonymous26-Nov-02 2:49

Anonymous

26-Nov-02 2:49

every c#'s object like a pointer in c++. But How can i get a pointer point to pointer (**) in c#?

I just work on a undo/redo engine in my c# application.
For example, there is two type of object to be edit in application

class A
{
string aa;
}

class B
{
int bb;
}

The edit operation change the many objects of type A or type B.
I hope to build a stack of object to store the string aa and int bb. Two objects to be cloned, one before the edit operation, another after it.

If the only way to change a memeber of a object is xx.yy = zz, i find it impossible to do the undo. Because i have to know the parent object (A or B) and which type of it (A or B) and judge in code whether to use aa or bb.

I doubt whether reflection ability in c# can help me.

But in c++ style, it is very easy to use object*. something like
*orgin = cloneBefore
or
*orgin = cloneAfter

Do i make some mistake? Please give me some suggestion!!
or any undo/redo engine written by c# or java in the world?

leppie26-Nov-02 6:26

leppie

26-Nov-02 6:26

I have no idea what you are trying to do, but you might want to look at the IClonable interface, and use that to make copies...

Hope this helps Smile | :)

DBHelper - SQL Stored Procedure Wrapper & Typed DataSet Generator for .NET popularity better now, thank you Smile | :)

Eric Gunnerson (msft)26-Nov-02 9:38

Eric Gunnerson (msft)

26-Nov-02 9:38

I think you can get the same behavior by simply creating a class to hold your object reference. You would declare instances of that rather than object*, and then you'll be able to look inside your class and change the reference.

Anonymous26-Nov-02 14:51

Anonymous

26-Nov-02 14:51

Yes, I think what you said is what i really want to do.
I need to bypass class A to access item aa in such an engine. But don't know whether c# permit it or not.

class A
{
string aa;
}

A someA;
someA.aa = "...";

In function calling, we can use "ref" keyword to have the object reference.
something like:

CallingFunc(ref someA.aa);

But i dont know how to store the object reference. "ref" seems only be used in calling parameters.

like:
store[i] = ref someA.aa ?

Can you show me some simple demo?

Thanks!!

Eric Gunnerson (msft)27-Nov-02 12:46

Eric Gunnerson (msft)

27-Nov-02 12:46

You'd need to write a class like:

class ObjectReference
{
public object reference; // this could be a property if you wanted...
}

Then, whenever you create something that needs to be undo-able, you wrap it in one of these objects and store the reference to ObjectReference.

Note that this is going to make your code pretty ugly, as you'll have to cast from object to the real type whenever you use an object.

NONCLIENTMETRICS marshalling

Andy Smith27-Nov-02 16:24

Andy Smith

27-Nov-02 16:24

You should look into using the Command Pattern[^] to create a undo/redo framework.

Matze25-Nov-02 20:31

25-Nov-02 20:31

Hi all,
I desperately need a hint guiding me the right direction...
I want to retrieve the NCM information using SystemParametersInfo. Well, to define the function call is rather easy, and the structure itself does not make lots of problems, too:

[StructLayout(LayoutKind.Sequential)]
public class NONCLIENTMETRICS
{
public int cbSize;
public int iBorderWidth;
public int iScrollWidth;
public int iScrollHeight;
public int iCaptionWidth;
public int iCaptionHeight;
public LOGFONT lfntCaptionFont;
public int iSMCaptionWidth;
public int iSMCaptionHeight;
public LOGFONT lfntSMCaptionFont;
public int iMenuWidth;
public int iMenuHeight;
public LOGFONT lfntMenuFont;
public LOGFONT lfntStatusFont;
public LOGFONT lfntMessageFont;

public NONCLIENTMETRICS()
{
cbSize = 340;
}
}

[StructLayout(LayoutKind.Sequential)]
public struct LOGFONT
{
public int lfHeight;
public int lfWidth;
public int lfEscapement;
public int lfOrientation;
public int lfWeight;
public byte lfItalic;
public byte lfUnderline;
public byte lfStrikeOut;
public byte lfCharSet;
public byte lfOutPrecision;
public byte lfClipPrecision;
public byte lfQuality;
public byte lfPitchAndFamily;
[MarshalAs(System.Runtime.InteropServices.UnmanagedType.ByValTStr, SizeConst=32)]
public string lfFaceName;

public static LOGFONT Empty
{
get
{... }
}
}

[DllImport("User32.dll"]
public static extern bool SystemParametersInfo(int Action, int Param, NONCLIENTMETRICS Param, int WinIni);

The call is

NONCLIENTMETRICS ncm = new NONCLIENTMETRICS();
bool b = SystemParametersInfo(SPI_GETNONCLIENTMETRICS, ncm.cbSize, ncm, 0);

And now I'm getting confused:
b is true, that means the call succeeded, but ncm has not been touched. Is there anything wrong with the structure layout?? At the end I tried all combinations, instead of a class I declared NCM as a structure and used ref, I tried the IntPtr version... nothing didn't help. And I know that it works since MS does similar to build the SystemInformation members (Menufont is contained in NCM, too).

Somewhere I'm blocked. Can anybody help??
Thanks and bye
Matze

leppie25-Nov-02 22:49

leppie

25-Nov-02 22:49

Matze wrote:
public NONCLIENTMETRICS()
{
cbSize = 340;
}

arrrg! Replace with

cbSize = Marshal.SizeOf(this);

Matze wrote:
DllImport("User32.dll"]
public static extern bool SystemParametersInfo(int Action, int Param, NONCLIENTMETRICS Param, int WinIni);

The call is

NONCLIENTMETRICS ncm = new NONCLIENTMETRICS();
bool b = SystemParametersInfo(SPI_GETNONCLIENTMETRICS, ncm.cbSize, ncm, 0);

The declaration and method calls doesnt match! Why are you passing ncm.cbSize. Some functions however need to be called twice. 1st to find out what size parameter they need, 2nd the actuall call. this mite be the case. See if values from other paramters change during the call.

Hope this helps Smile | :)

DBHelper - SQL Stored Procedure Wrapper & Typed DataSet Generator for .NET low popularity, please visit Smile | :)

Matze25-Nov-02 23:07

25-Nov-02 23:07

Hi leppie,
thanks for the answer!

leppie wrote:
bool b = SystemParametersInfo(SPI_GETNONCLIENTMETRICS, ncm.cbSize, ncm, 0);

The declaration and method calls doesnt match! Why are you passing ncm.cbSize. Some functions however need to be called twice. 1st to find out what size parameter they need, 2nd the actuall call. this mite be the case. See if values from other paramters change during the call.

Hmm, the documentation states that for the GETNONCLIENTMAETRICS action the size of NCM must be told as second parameter, that's why I passed it (and so does MS, as one can see in the Decompiler;)). Actually, when I pass anything else than 340 (==Marshall..;)) the function returns false. No values are changed, unfortunately Cry | :((

leppie wrote:
public NONCLIENTMETRICS()
{
cbSize = 340;
}

arrrg! Replace with

cbSize = Marshal.SizeOf(this);

Yepp, of course I did this, but I thought a number is more informative in the message Wink | ;)

Stephane Rodriguez.25-Nov-02 23:48

Stephane Rodriguez.

25-Nov-02 23:48

Replace the DllImport declaration with :

[DllImport("User32.dll")]
public static extern bool SystemParametersInfo(int Action, 
                                     int Param, 
                                     IntPtr lpParam, 
                                     int WinIni);

And replace the method call with :

const int SPI_GETNONCLIENTMETRICS = 41;

NONCLIENTMETRICS ncm = new NONCLIENTMETRICS();

int size = ncm.cbSize = Marshal.SizeOf(typeof(NONCLIENTMETRICS));
IntPtr pncmetrics = Marshal.AllocHGlobal(size);
Marshal.StructureToPtr(ncm, pncmetrics, true);
bool b = SystemParametersInfo(SPI_GETNONCLIENTMETRICS, size, pncmetrics, 0); 
Marshal.PtrToStructure(pncmetrics,ncm); 
Marshal.FreeHGlobal(pncmetrics);

The .NET 1.0 marshaller has some troubles when it comes to marshalling LPStruct. Hopefully, this will be fixed in 1.1 (may be someone using the Everett beta could tell us whether it is fixed or not).

Matze26-Nov-02 0:16

26-Nov-02 0:16

Hi Rod,
thanks a lot, that sounds feasible. Will give you immediate feedback today evening when I'm back from the customer..
Bye
Matze

Anonymous26-Nov-02 5:19

Anonymous

26-Nov-02 5:19

Oh whow, you are my hero Rose | [Rose]

- it works!! Yipppieeeehh!!! You made my day, no, my month;) How for heavens sake did find that out???
Thanks and bye
Matze

leppie26-Nov-02 8:23

leppie

26-Nov-02 8:23

I thought this (your fix method) is whats happening normally (inside .NET)when you pass a struct/class into a unmanaged function?

I do prefer to invoke unmanaged functions as you have shown above as I allways feel I have more control...although a bit more work.

Smile | :)

DBHelper - SQL Stored Procedure Wrapper & Typed DataSet Generator for .NET popularity better now, thank you Smile | :)

Richard Deeming26-Nov-02 6:21

Richard Deeming

26-Nov-02 6:21

Option 2:

Change the NONCLIENTMETRICS to a struct (NB: You'll have to remove the constructor.)

Change the declaration to:

[DllImport("User32.dll")]
public static extern bool SystemParametersInfo(int Action, 
    int uiParam, ref NONCLIENTMETRICS pvParam, int WinIni);

Change the call to:

NONCLIENTMETRICS ncm = new NONCLIENTMETRICS();
ncm.cbSize = Marshal.SizeOf(ncm);
bool b = SystemParametersInfo(SPI_GETNONCLIENTMETRICS, 
    ncm.cbSize, ref ncm, 0);

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

Matze26-Nov-02 19:27

26-Nov-02 19:27

Hi Richard,
this was my very first try, before I changed NCM to a class (and before I read any documentation;)). The call succeeds, too, but NCM remains at its initial state...
Referring to leppie I would prefer this method, too, since it's much more NET like. Does this call succeed on your machine?
Thanks and bye
Matze

Richard Deeming26-Nov-02 22:38

Richard Deeming

26-Nov-02 22:38

Here's the code I used, and the output on my XP Pro machine:

using System;
using System.Runtime.InteropServices;
 
class App
{
    [StructLayout(LayoutKind.Sequential)]
    public struct LOGFONT
    {
        public int lfHeight;
        public int lfWidth;
        public int lfEscapement;
        public int lfOrientation;
        public int lfWeight;
        public byte lfItalic;
        public byte lfUnderline;
        public byte lfStrikeOut;
        public byte lfCharSet;
        public byte lfOutPrecision;
        public byte lfClipPrecision;
        public byte lfQuality;
        public byte lfPitchAndFamily;
        
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst=32)]
        public string lfFaceName;
    }
    
    [StructLayout(LayoutKind.Sequential)]
    public struct NONCLIENTMETRICS
    {
        public int cbSize;
        public int iBorderWidth;
        public int iScrollWidth;
        public int iScrollHeight;
        public int iCaptionWidth;
        public int iCaptionHeight;
        public LOGFONT  lfntCaptionFont;
        public int iSMCaptionWidth;
        public int iSMCaptionHeight;
        public LOGFONT lfntSMCaptionFont;
        public int iMenuWidth;
        public int iMenuHeight;
        public LOGFONT lfntMenuFont;
        public LOGFONT lfntStatusFont;
        public LOGFONT lfntMessageFont;
    }
    
    [DllImport("User32.dll")]
    public static extern bool SystemParametersInfo(
        int Action, int uiParam, 
        ref NONCLIENTMETRICS pvParam, int WinIni);
    
    static void Main()
    {
        const int SPI_GETNONCLIENTMETRICS = 41;
        
        try
        {
            NONCLIENTMETRICS ncm = new NONCLIENTMETRICS();
            ncm.cbSize = Marshal.SizeOf(ncm);
            
            bool b = SystemParametersInfo(
                SPI_GETNONCLIENTMETRICS, 
                ncm.cbSize, ref ncm, 0);
            
            if (b)
            {
                Console.WriteLine("Border Width: {0}", 
                    ncm.iBorderWidth);
    
                Console.WriteLine("Scroll Width: {0}", 
                    ncm.iScrollWidth);
    
                Console.WriteLine("Caption Font: {0}", 
                    ncm.lfntCaptionFont.lfFaceName);
            }
            else
                Console.WriteLine("Failed");
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.ToString());
        }
    }
}

Output:

Border Width: 1
Scroll Width: 17
Caption Font: Trebuchet MS

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

Matze14-Dec-02 0:50