Using handler OnBegindrag with CTreeCtrl - c++

Question

I have class MyCTreeCtrl and I want to add message handler like:
void MyCTreeCtrl::OnBegindrag(NMHDR *pNMHDR, LRESULT *pResult)
{
}
What should I write between:
BEGIN_MESSAGE_MAP(MyCTreeCtrl, CTreeCtrl)
END_MESSAGE_MAP()
for creating BEGINDRAG handler.
Can't you advice me some literature about message handling in MFC? Thanks.

Answer 1

You should not deal with message map trying to create handlers yourself. For most messages, wizard is going to add the code for you.
For tree control in the dialog for example, you can select tree control in the resource editor and choose Add Event Handler (There are also other ways of inserting message handler using class view and properties). It is unfortunate that MS named it an event handler while in reality it is notification message handler for control specific notification code; in your case it is TVN_BEGINDRAG.
Wizard inserts appropriate entries into a message map:
ON_NOTIFY(TVN_BEGINDRAG, IDC_TREE_DRAG, &CYourDlg::OnTvnBegindragTreeDrag)
Adds declaration in .h file:
afx_msg void OnTvnBegindragTreeDrag(NMHDR *pNMHDR, LRESULT *pResult);
and implementation (definition) on .cpp file:
void CYourDlg::OnTvnBegindragTreeDrag(NMHDR *pNMHDR, LRESULT *pResult)
{
LPNMTREEVIEW pNMTreeView = reinterpret_cast<LPNMTREEVIEW>(pNMHDR);
// TODO: Add your control notification handler code here
*pResult = 0;
}
In the nutshell:
Message map is the way MFC was design for the flexibility of inserting message handlers. As for any Win32 application, message handler is called from windows procedure; in MFC it is MFC window procedure that all controls are subclassed with.
The message map is the static array of AFX_MSGMAP_ENTRY structures:
struct AFX_MSGMAP_ENTRY
{
UINT nMessage; // windows message
UINT nCode; // control code or WM_NOTIFY code
UINT nID; // control ID (or 0 for windows messages)
UINT nLastID; // used for entries specifying a range of control id's
UINT_PTR nSig; // signature type (action) or pointer to message #
AFX_PMSG pfn; // routine to call (or special value)
};
MFC window procedure gets this map, search for an entry for specific signature (nSig) and if signature of the entry matches, calls appropriate function (pfn).
Each message entry in the map uses specific macro that expands to this structure.
In your case it is ON_NOTIFY, since message is MW_NOTIFY. You will also notice the notification code TVN_BEGINDRAG.
In case you want to create message entry for a message that is not in the wizard database, or for custom message, you have couple of choices, ON_MESSAGE you can use in following manner:
Macro goes into a message map and declaration and definition that go into header and cpp files.
ON_MESSAGE(WM_CUSTOM_MESSAGE, OnCustomMessage)
LRESULT CTreeCtrlDragSampleDlg::OnCustomMessage(WPARAM wParam, LPARAM lParam)
{
return 0;
}
afx_msg LRESULT OnCustomMessage(WPARAM wParam, LPARAM lParam);
Other choices: ON_COMMAND, ON_CONTROL that map WM_COMMAND messages from window or windows common control.
More info:
http://msdn.microsoft.com/en-us/library/6d1asasd(v=vs.100).aspx for VS 2010