Truble with GetDC()

[Iwanttolearn]

I have an app which i draw a PNG on the button and all works great until i want to redraw the whole screen.

when i try to redraw the whole screen it gives me an exception and points to this part of afxwin2.h

_AFXWIN_INLINE CDC* CWnd::GetDC()
	{ ASSERT(::IsWindow(m_hWnd)); return CDC::FromHandle(::GetDC(m_hWnd)); }

here's my code:

void CODBIIMakerDatabaseDlg::DrawBackground(CDC *dc/*=0*/)
{
	Gdiplus::Image * BG;//GDI+ Background variable

	if(!dc)
		dc = GetDC();

	Gdiplus::Graphics grpx(*dc);//GDI Graphics container
	Gdiplus::Rect rect(0,0,473,261);//GDI image pos and size

	BG = Gdiplus::Image::FromFile(L"Image\\BackGround.png",FALSE);

	grpx.DrawImage(BG,rect);
}

It works great the first time DrawBackground is called but when i call DrawBackground with this DrawBackground(0);

I get an exception when the if(!dc) is executed.

Am i Calling GetDC() wrong?

[anders43]

try ::GetDC(NULL)

[Iwanttolearn]

It gives me

cannot convert from 'HDC' to 'CDC *'

i need to handle CDC not HDC.


Thanks for ur help ^_^.

[z05DSL3A]

Are you talking about redrawing the background of your dialog box?

You should handle the WM_ERASEBKGND message and put your drawing code in there. If you want your dialog to be redrawn, you call Invalidate(true), you do not call drawing functions directly.

[anders43]

as far as I understood your issue you wanted to redraw the whole screen (i.e. using GetDC(NULL) && I am also assuming you are using MFC) you need to convert the HDC to a CDC*. You can for instance do that through CDC::Attach (or IIRC through the ctor)

[Iwanttolearn]

I don't know how to do that.

I will appreciate if you can show me an example?

[anders43]

E.g.

dc = new CDC;
dc->Attach( ::GetDC(NULL) );

...

dc->Detach();

[z05DSL3A]

Drawing all over the 'screen' [via GetDC(NULL) ] seems to be a very foolhardy thing to be doing and encouraging such application behaviour also seems foolhardy.

[anders43]

I believe that everybody I reply to have enough intelligence to eventually figure out if something is good or bad - it is part of the learning process.

If he would ask if it was good or bad that would be another matter but giving unsolicited advice is just unnecessary noise since we don't know all the context/requirements.

[z05DSL3A]

I believe that everybody I reply to have enough intelligence to eventually figure out if something is good or bad - it is part of the learning process.

Now that I do find worrying, it makes it sound like you would give an answer knowing that the person is on the wrong track: That's what they asked, let them crash and burn later on, they’ll learn from that.

[Iwanttolearn]

If i Invalidate the screen just flashes between gray and the BG Image.

[z05DSL3A]

Iwanttolearn,

Do I take it that you have handled WM_ERASEBKGND?

If so OnEraseBkgnd should be like this:

BOOL CODBIIMakerDatabaseDlg::OnEraseBkgnd(CDC* pDC)
{
    // TODO: your Drawing code

    return true; // Do not call CDialog::OnEraseBkgnd(pDC);
}

If not, can you tell us what you are doing? (with code)

[Iwanttolearn]

My Dialog

// ODBII  Maker DatabaseDlg.cpp : implementation file
//

#include "stdafx.h"
#include "ODBII  Maker Database.h"
#include "ODBII  Maker DatabaseDlg.h"
#include "SearchButton.h"
#include <fstream>
#include <gdiplus.h>
#include <GdiPlusEnums.h>

#pragma comment (lib,"gdiplus.lib")

using namespace std;

fstream database;

CString ItemText;
int mark;

#ifdef _DEBUG
#define new DEBUG_NEW
#endif


// CAboutDlg dialog used for App About

class CAboutDlg : public CDialog
{
public:
	CAboutDlg();

// Dialog Data
	enum { IDD = IDD_ABOUTBOX };

	protected:
	virtual void DoDataExchange(CDataExchange* pDX);    // DDX/DDV support

// Implementation
protected:
	DECLARE_MESSAGE_MAP()
};

CAboutDlg::CAboutDlg() : CDialog(CAboutDlg::IDD)
{
}

void CAboutDlg::DoDataExchange(CDataExchange* pDX)
{
	CDialog::DoDataExchange(pDX);
}

BEGIN_MESSAGE_MAP(CAboutDlg, CDialog)
END_MESSAGE_MAP()


// CODBIIMakerDatabaseDlg dialog




CODBIIMakerDatabaseDlg::CODBIIMakerDatabaseDlg(CWnd* pParent /*=NULL*/)
	: CDialog(CODBIIMakerDatabaseDlg::IDD, pParent)
{
	m_hIcon = AfxGetApp()->LoadIcon(IDR_MAINFRAME);
}

void CODBIIMakerDatabaseDlg::DoDataExchange(CDataExchange* pDX)
{
	CDialog::DoDataExchange(pDX);
	DDX_Control(pDX, IDC_LIST1, m_Maker);
	DDX_Control(pDX, IDC_FIND, Search);
	DDX_Control(pDX, IDC_CODE, m_Meaning);
	DDX_Control(pDX, IDC_Meaning, m_Code);
}

BEGIN_MESSAGE_MAP(CODBIIMakerDatabaseDlg, CDialog)
	ON_WM_SYSCOMMAND()
	ON_WM_PAINT()
	ON_WM_QUERYDRAGICON()
	ON_BN_CLICKED(IDC_FIND, &CODBIIMakerDatabaseDlg::OnBnClickedFind)
	ON_WM_ERASEBKGND()
END_MESSAGE_MAP()


// CODBIIMakerDatabaseDlg message handlers

BOOL CODBIIMakerDatabaseDlg::OnInitDialog()
{
	CDialog::OnInitDialog();

	// Add "About..." menu item to system menu.

	// IDM_ABOUTBOX must be in the system command range.
	ASSERT((IDM_ABOUTBOX & 0xFFF0) == IDM_ABOUTBOX);
	ASSERT(IDM_ABOUTBOX < 0xF000);

	CMenu* pSysMenu = GetSystemMenu(FALSE);
	if (pSysMenu != NULL)
	{
		BOOL bNameValid;
		CString strAboutMenu;
		bNameValid = strAboutMenu.LoadString(IDS_ABOUTBOX);
		ASSERT(bNameValid);
		if (!strAboutMenu.IsEmpty())
		{
			pSysMenu->AppendMenu(MF_SEPARATOR);
			pSysMenu->AppendMenu(MF_STRING, IDM_ABOUTBOX, strAboutMenu);
		}
	}

	// Set the icon for this dialog.  The framework does this automatically
	//  when the application's main window is not a dialog
	SetIcon(m_hIcon, TRUE);			// Set big icon
	SetIcon(m_hIcon, FALSE);		// Set small icon

	// TODO: Add extra initialization here
	Gdiplus::GdiplusStartupInput gdiplusstartupinput;
	Gdiplus::GdiplusStartup(&gdiplusToken,&gdiplusstartupinput,NULL);
	char Maker[MAX_PATH];
	m_Maker.InsertColumn(0,"");
	m_Maker.SetColumnWidth(0,180);

	database.open("Manufacturers//Manufacturer.txt",fstream::in);

	while (database.getline(Maker,sizeof(Maker)) != 0)
			{
				m_Maker.InsertItem(0,Maker);
		}

	database.clear();
	database.close();

	return TRUE;  // return TRUE  unless you set the focus to a control
}

void CODBIIMakerDatabaseDlg::OnSysCommand(UINT nID, LPARAM lParam)
{
	if ((nID & 0xFFF0) == IDM_ABOUTBOX)
	{
		CAboutDlg dlgAbout;
		dlgAbout.DoModal();
	}
	else
	{
		CDialog::OnSysCommand(nID, lParam);
	}
}

// If you add a minimize button to your dialog, you will need the code below
//  to draw the icon.  For MFC applications using the document/view model,
//  this is automatically done for you by the framework.

void CODBIIMakerDatabaseDlg::OnPaint()
{
	CPaintDC dc(this); // device context for painting

	if (IsIconic())
	{

		SendMessage(WM_ICONERASEBKGND, reinterpret_cast<WPARAM>(dc.GetSafeHdc()), 0);

		// Center icon in client rectangle
		int cxIcon = GetSystemMetrics(SM_CXICON);
		int cyIcon = GetSystemMetrics(SM_CYICON);
		CRect rect;
		GetClientRect(&rect);
		int x = (rect.Width() - cxIcon + 1) / 2;
		int y = (rect.Height() - cyIcon + 1) / 2;

		// Draw the icon
		dc.DrawIcon(x, y, m_hIcon);
	}
	else
	{
		CDialog::OnPaint();
	}
}

// The system calls this function to obtain the cursor to display while the user drags
//  the minimized window.
HCURSOR CODBIIMakerDatabaseDlg::OnQueryDragIcon()
{
	return static_cast<HCURSOR>(m_hIcon);
}


void CODBIIMakerDatabaseDlg::OnBnClickedFind()
{
	//Search for the Code in the Database
	CString Search;
	CString Folder;
	char Temp[MAX_PATH];
	char Code[MAX_PATH];
	char Meaning[MAX_PATH];

	m_Meaning.SetWindowTextA("");

	Search = "[";
	m_Code.GetWindowTextA(Temp,sizeof(Temp));
	Search += Temp;
	Search += "]";

	if(m_Maker.GetSelectedCount() > 0)
		{
		//get the selected items number in the Listcontrol
		mark = m_Maker.GetSelectionMark();
		//get the text of the selected item in the listctrl
		ItemText = m_Maker.GetItemText(mark,NULL);
		//open the file for reading
		Folder = "Manufacturers\\";
		Folder += ItemText;
		Folder += ".txt";
		database.open(Folder,fstream::in);


			while (database.getline(Code,sizeof(Code)) != 0)
			{
		//if the Description line matches with the word searched
		//get the Codes Meaning and display it
				if(strcmp(Code,Search) == 0)
				{
					database.getline(Meaning,MAX_PATH);
					m_Meaning.SetWindowTextA(Meaning);
			}

		}
	}

	database.close();
	database.clear();
}
BOOL CODBIIMakerDatabaseDlg::OnEraseBkgnd(CDC* pDC)
{
	// TODO: Add your message handler code here and/or call default
	Gdiplus::Image * BG;

	Gdiplus::Graphics grpx(*pDC);//GDI Graphics container
	Gdiplus::Rect rect(0,0,473,261);//GDI image pos and size

	BG = Gdiplus::Image::FromFile(L"Image\\BackGround.png",FALSE);

	grpx.DrawImage(BG,rect);

	return true;
}

and The Button

// SearchButton.cpp : implementation file
//

#include "stdafx.h"
#include "ODBII  Maker Database.h"
#include "ODBII  Maker DatabaseDlg.h"
#include "SearchButton.h"
#include <gdiplus.h>

#pragma comment (lib,"gdiplus.lib")


// SearchButton

IMPLEMENT_DYNAMIC(SearchButton, CButton)

SearchButton::SearchButton()
{
	Gdiplus::GdiplusStartupInput gdiplusstartupinput;
	Gdiplus::GdiplusStartup(&gdiplusToken,&gdiplusstartupinput,NULL);

	ButtonUp = Gdiplus::Image::FromFile(L"Image\\Button1.png",FALSE);
	ButtonDown = Gdiplus::Image::FromFile(L"Image\\Button2.png",FALSE);
}

SearchButton::~SearchButton()
{
	Gdiplus::GdiplusShutdown(gdiplusToken);
}


BEGIN_MESSAGE_MAP(SearchButton, CButton)
	ON_WM_ERASEBKGND()
END_MESSAGE_MAP()



// SearchButton message handlers





void SearchButton::DrawItem(LPDRAWITEMSTRUCT lpDrawItemStruct)
{
CDC dc;

dc.Attach(lpDrawItemStruct->hDC);

CRect rt;

rt = lpDrawItemStruct->rcItem;

Gdiplus::Graphics grpx(dc);

Gdiplus::Rect rect(0,0,90,90);

UINT State = lpDrawItemStruct->itemState;

if((State & ODS_SELECTED))
{
	grpx.DrawImage(ButtonUp,rect);
}
else
{
	grpx.DrawImage(ButtonDown,rect);
}

dc.Detach();

}

BOOL SearchButton::OnEraseBkgnd(CDC* pDC)
{
	// TODO: Add your message handler code here and/or call default

	return TRUE;
}

[z05DSL3A]

I think you are going to have to more detail about exactly what the problem is. I remember taking to you about your button class^[1], but the code you have presented here does not resemble that.

[1] http://www.cplusplus.com/forum/windows/7130/

[Iwanttolearn]

The thing is that every time i try a solution another problem pops out.

People tell me to use Invalidate and InvalidateRect but both of them don't work.

If i use Invalidate or InvalidateRect in my dialog,my BG just redraws on top of all my stuff.

*Edit*

Here is the Upload of my Project.

http://rapidshare.com/files/194030366/ODBII__Maker_Database.rar

[z05DSL3A]

If i use Invalidate or InvalidateRect in my dialog,my BG just redraws on top of all my stuff.

I'm not sure what you mean by "...all my stuff." but it sounds like "all your stuff" is being arbitrarily drawn onto the dialog box surface and not in response to any windows draw message. As a result, any time that Windows issues redraw messages to your app, it can only redrawn the parts that you have put in the correct place any arbitrarily code can not be called so it does not get redrawn.

[anders43]

OP, normally when it comes to dialogs and processing information one splits the visual part from the actual data part by having a thread handle the reading of data/searching. If you have it all in one thread (as it looks, although I haven't looked at your project files) then while you are doing the search it may affect the painting of your dialog.

There are many online sources that show examples how to do that like codeguru which is very mfc-oriented.

One of my favorite resources for MFC:
http://www.flounder.com/workerthreads.htm

[z05DSL3A]

Anders43, while hiving of long running processes to is important, the OP is trying to get his owner drawn 'stuff' sorted.

I haven't got a good 'single source' to help him learn this, maybe you have?