Using a class callback for a custom control?
I'm creating a custom control class and since I want complete control of it, I register the class and want to use the class's
LRESULT CALLBACK OGLTOOLBAR::ToolProc(HWND, UINT, WPARAM, LPARAM)
but it's not letting me.
I'm doing:
HWND OGLTOOLBAR::create(HWND parent,HINSTANCE hInst, int *toolWidthPtr)
{
if (toolhWnd != NULL)
{
return toolhWnd;
}
toolWidth = toolWidthPtr;
ZeroMemory(&rwc,size开发者_开发百科of(rwc));
rwc.lpszClassName = TEXT("OGLTool");
rwc.hbrBackground = GetSysColorBrush(COLOR_BTNSHADOW);
rwc.lpfnWndProc = (WNDPROC)ToolProc;
rwc.hCursor = LoadCursor(0, IDC_ARROW);
RegisterClass(&rwc);
toolhWnd = CreateWindowEx(NULL, rwc.lpszClassName,NULL,
WS_CHILD | WS_VISIBLE,
0, 0, *toolWidth, 900, parent, 0, NULL, 0);
return toolhWnd;
}
what is the correct way of doing this?
Thanks
compiler says: Error 1 error C2440: 'type cast' : cannot convert from 'overloaded-function' to 'WNDPROC'
If ToolProc isn't a static member, you can't pass a member function pointer as a callback like that, assuming you want ToolProc to be a non-static function, you can create a static member function, and use the GetWindowLong/SetWindowLong and the GWL_USERDATA area, to store a pointer to the current object(this), and have a static callback call the individual objects callback function, that can utilize the individual objects data members.
Assuming that ToolProc is not a static member of your OGLTOOLBAR class, you have to tie the this pointer of the object to the window handle, you can do this like so:
void OGLTOOLBAR::SetObjectToHWnd( HWND hWnd, LPARAM lParam )
{
LPCREATESTRUCT cs = reinterpret_cast<LPCREATESTRUCT>(lParam);
OGLTOOLBAR *pWnd = reinterpret_cast<OGLTOOLBAR*>(cs->lpCreateParams);
SetLastError( 0 );
if( !SetWindowLong( hWnd, GWL_USERDATA, reinterpret_cast<long>(pWnd) )
&& GetLastError() )
//Do something about the error
}
OGLTOOLBAR *OGLTOOLBAR::GetObjectFromHWnd( HWND hWnd )
{
return reinterpret_cast<OGLTOOLBAR*>(GetWindowLong(hWnd,GWL_USERDATA));
}
And then you have a static WndProc(Or ToolProc) member function like this:
LRESULT OGLTOOLBAR::StaticToolProc( HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam )
{
if( uMsg == WM_NCCREATE )
SetObjectToHwnd( hWnd, lParam );
Window *pWnd = GetObjectFromWnd( hWnd );
if( pWnd )
return pWnd->ToolProc( hWnd, uMsg, wParam, lParam );
else
return DefWindowProc( hWnd, uMsg, wParam, lParam );
}
And then when you call the CreateWindow
function in OGLTOOLBAR::create
, pass reinterpret_cast<void*>(this)
as the lpParam
argument(The last one).
And each OGLTOOLBAR object will then have it's own ToolProc called for each instance, through the StaticToolProc function. Or at least I believe this should work.
Is ToolProc a static member? You can't pass member function pointers or functors as function pointers. C APIs only work in function pointers.
There's usually a way to tie "client data" to an object so that it is passed to the callback when triggered. You can use that information to carry instance specific data so that a static or global function can call the member variable in the correct class.
精彩评论