Help, my texts is erased when drag the window..

Yep I do, in your WM_PAINT handler simply redraw the text using TextOut I guess...

And your welcome. :)

look at this thread:
http://www.dev-archive.com/forum/showthread.php?t=437491

it is the same thing, but you are writing text instead of drawing lines.

you can either store all the text so that you can write it all again for each WM_PAINT message, or you can use a memory DC that is drawn to the screen at each refresh.

I didn't copy all the code because it's kind of long, so as you can see if the button, magnifyOn, get clicked then it will output the text. If I keep pressing the same button to print more than one lines of text then I run into problem as I described earlier.

Feel free to ask me any question about my code, and thanks for your guys time looking at it.

//global variables
int textPosition = 350;
const int maxDisplayLine = 5;
int currentDisplayLinePosition = 0;
int textLength = 0;
LPSTR id = NULL;

//this function will update all the values for the global variables so they can
//be used when the WM_PAINT calls
void zoomTextDescription(LPSTR descriptionID, int length, int posY)
{

HWND menuWindow = FindWindow(NULL, TEXT("My Window"));

//display text 5 lines maximum
if(currentDisplayLinePosition < maxDisplayLine)
{
currentDisplayLinePosition +=1;
textPosition = posY;
textLength = length;
id = descriptionID;
InvalidateRect(menuWindow, NULL, FALSE);
}
else //even though the condition is fail, but there is one text description
{ //left of that fail condition need to display

currentDisplayLinePosition = 0;
textPosition = 350;
textLength = length;
id = descriptionID;
InvalidateRect(menuWindow, NULL, FALSE);
}
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
switch(message)
{

case WM_COMMAND:

switch(LOWORD(wParam))
{

case ID_MENU_ZOOMme: //menu command
{
//dialog box
DialogBox(g_hInstance, MAKEINTRESOURCE(IDD_zoomCommand), hwnd, AboutDlgProc);
}
break;

case WM_PAINT:
{

HDC hdc = GetDC(hwnd);
TextOut(hdc, 5, textPosition, (LPCWSTR)id, textLength);
ReleaseDC(hwnd, hdc);

}
break;

case WM_DESTROY:
{
PostQuitMessage(0);
}
break;
}

return DefWindowProc(hwnd, message, wParam, lParam);
}

BOOL CALLBACK AboutDlgProc(HWND dlg, UINT message, WPARAM wParam, LPARAM lParam)
{

switch(message)
{
case WM_COMMAND:
switch(LOWORD(wParam))
{

case IDC_magnifyOn: //magnifyOn button
{
zoomTextDescription((LPSTR)TEXT("Magnify On"), (int)strlen("Magnify On"), textPosition +=18);

}
break;
case SC_CLOSE:
case WM_DESTROY:
//case WM_QUIT:
case WM_CLOSE:
{

EndDialog(dlg, 0);
PostQuitMessage(0);
return TRUE;

}
break;

}//end of COMMAND message switch case

}//end of message switch case

return FALSE;
}

In your code you haven't added the second piece of text.

I'm sorry I don't know if I can help you because I simply don't understand.

i'm afraid that using a memory DC is pretty much the easiest way to do it.

i suppose you could do a dirty fix of
case WM_ERASEBKGND :
{
return 0;
}

this will stop the window being erased when you drag it (before it is redrawn with only one text message) but you will still get all sorts of problems when you drag it off of the screen or cover it with another window etc..

you have to keep a record of what you want to draw yourself.

you can do this two ways:
(1) keep a list of all the strings somewhere (e.g. in an array of strings) and then TextOut() ALL of the strings each time you redraw the window.

(2) draw them once to a bitmap in a memory DC, and just draw the memory DC to the screen at each refresh.

it depends what you want the strings for and why you are displaying them as to which option is most appropriate. there are probably other ways, but variations on a theme - the important thing is that windows is not going to remember things for you, if you want to draw something again you have to store the information somewhere.

Thanks you for your suggestion. I will create the array and store information just like you suggested in the first option.