C / C++ / MFC

28-Feb-06 6:54

Is there a way of sending my class a pointer to my view's DC. I would like to draw to the DC and then "blit" it back to the screen. Until now I have only been able to get the DC for the main window.

Thanks.

PJ Arends28-Feb-06 7:40

PJ Arends

28-Feb-06 7:40

CFrameWnd::GetActiveView will return a pointer to your CView derived window, you can call GetDC on that view

You may be right
I may be crazy
But it just may be a lunatic you’re looking for
-- Billy Joel --

Within you lies the power for good - Use it!

masnu28-Feb-06 7:59

28-Feb-06 7:59

I tried what you suggested and I get an "illegal call of non-static member function" error.

CView* pView = CFrameWnd::GetActiveView();<br />
CDC* pDC = myview->GetDC();

I am new to the whole MFC programming scene so I am sure I am doing something really silly.

Thanks for the help.

-- modified at 14:00 Tuesday 28th February, 2006

David Crow28-Feb-06 8:12

28-Feb-06 8:12

masnu wrote:
CView* pView = CFrameWnd::GetActiveView();

GetActiveView() is not a static function (i.e., one that can be called without an actual object). You must call it in the context of a CFrameWnd object, not CFrameWnd itself.

"Let us be thankful for the fools. But for them the rest of us could not succeed." - Mark Twain

"There is no death, only a change of worlds." - Native American Proverb

masnu28-Feb-06 8:52

28-Feb-06 8:52

David,

From what you said I assume I need to put the code in my CMainFrame class, which I did. I no longer get a compiler error, but I get an access violation error in the objcore.cpp file:

BOOL CObject::IsKindOf(const CRuntimeClass* pClass) const<br />
{<br />
	ENSURE(this != NULL);<br />
	// it better be in valid memory, at least for CObject size<br />
	ASSERT(AfxIsValidAddress(this, sizeof(CObject)));<br />
<br />
	// simple SI case<br />
	CRuntimeClass* pClassThis = GetRuntimeClass();   //ERROR HERE<br />
<br />
	ENSURE(pClassThis);<br />
	return pClassThis->IsDerivedFrom(pClass);<br />
}

What I have is:

void CMainFrame::Scroll()<br />
{<br />
	CDC* pDC = CFrameWnd::GetActiveView()->GetDC();<br />
<br />
	CStripChart* pStrip;<br />
	pStrip->Scroll(pDC);<br />
}

Any suggestions?

Thanks.

David Crow28-Feb-06 9:05

28-Feb-06 9:05

masnu wrote:
CStripChart* pStrip;
pStrip->Scroll(pDC);

This looks suspect. How has pStrip been initialized?

"Let us be thankful for the fools. But for them the rest of us could not succeed." - Mark Twain

"There is no death, only a change of worlds." - Native American Proverb

masnu28-Feb-06 9:37

28-Feb-06 9:37

When I debug, that code doesn't even run. The problem occurs when

CDC* pDC = CFrameWnd::GetActiveView()->GetDC();

is executed.

CStripChart is just a class I created to accept a DC and draw a grid to it and plot what ever data is sent to it. I have scroll function as a seperate thread. Could this be a problem?

Is there any way I can get a pointer to the view's DC and pass it to my class for furture use? Or would I need to pass a new DC everytime I wanted to update my window?

David Crow28-Feb-06 10:01

28-Feb-06 10:01

What does GetActiveView() return? If it is NULL, then dereferencing the pointer will cause problems.

"Let us be thankful for the fools. But for them the rest of us could not succeed." - Mark Twain

"There is no death, only a change of worlds." - Native American Proverb

masnu28-Feb-06 10:34

28-Feb-06 10:34

It doesn't return anything. I get the error before it returns.

David Crow28-Feb-06 10:40

28-Feb-06 10:40

When/how is CMainFrame::Scroll() called?

masnu wrote:
I get the error before it returns.

Since GetActiveView() and GetDC() are called within the same statement, are you sure?

"Let us be thankful for the fools. But for them the rest of us could not succeed." - Mark Twain

"There is no death, only a change of worlds." - Native American Proverb

masnu28-Feb-06 10:43

28-Feb-06 10:43

As a quick test I modified the app's file open command:

ON_COMMAND(ID_FILE_OPEN, &CMainFrame::Scroll)

David Crow28-Feb-06 10:45

28-Feb-06 10:45

masnu wrote:
ON_COMMAND(ID_FILE_OPEN, &CMainFrame::Scroll)

What is the ampersand doing there?

"Let us be thankful for the fools. But for them the rest of us could not succeed." - Mark Twain

"There is no death, only a change of worlds." - Native American Proverb

masnu28-Feb-06 10:54

28-Feb-06 10:54

I just followed the same format as all the other ON_COMMAND declarations. I tried runnig the program without the ampersand and I still get the same problem.

PJ Arends28-Feb-06 11:00

PJ Arends

28-Feb-06 11:00

void CMainFrame::Scroll()
{
CDC *pDC = this->GetActiveView()->GetDC();

You may be right
I may be crazy
But it just may be a lunatic you’re looking for
-- Billy Joel --

Within you lies the power for good - Use it!

How Thread Run Parallely

zahid_ash28-Feb-06 6:52

zahid_ash

28-Feb-06 6:52

I have created my own class CThread inherited from CWinThread,
I am Starting Threads using

for loop begin
AfxBeginThread(RUNTIME_CLASS(CThread));
for loop ends

I have created 15 thread in a loop, will they run parallely or with the time slice scheduling, Actualy I want that they should run parralelly , so that i can write in 15 different file simaltinoiusly.

I want to work fast on these threads.

Regards.

David Crow28-Feb-06 7:13

28-Feb-06 7:13

zahid_ash wrote:
...I have created 15 thread in a loop, will they run parallely or with the time slice scheduling...

They will never run in parallel on a uniprocessor machine.

"Let us be thankful for the fools. But for them the rest of us could not succeed." - Mark Twain

"There is no death, only a change of worlds." - Native American Proverb

zahid_ash28-Feb-06 7:42

zahid_ash

28-Feb-06 7:42

Is there any technique to write in the in the different file parallely or read from them .

i want to shorten the read write time

Regards.

Maximilien28-Feb-06 7:46

Maximilien

28-Feb-06 7:46

not with a single CPU computer.

Maximilien Lincourt
Your Head A Splode - Strong Bad

David Crow28-Feb-06 7:50

28-Feb-06 7:50

I think so, as long as the read and write operations are not happening at the exact spot in the file. See LockFile() for more.

zahid_ash wrote:
i want to shorten the read write time

Well, creating a bunch of threads on a uniprocessor machine is one way to not "shorten the read write time." The overhead of context-switching between all of the threads will be your demise.

"Let us be thankful for the fools. But for them the rest of us could not succeed." - Mark Twain

"There is no death, only a change of worlds." - Native American Proverb