CCreateContext Structure

Статья
10/16/2008

The framework uses the CCreateContext structure when it creates the frame windows and views associated with a document.

struct CCreateContext

Заметки

CCreateContext is a structure and does not have a base class.

When creating a window, the values in this structure provide information used to connect the components that make up a document and the view of its data. You will only need to use CCreateContext if you are overriding parts of the creation process.

A CCreateContext structure contains pointers to the document, the frame window, the view, and the document template. It also contains a pointer to a CRuntimeClass that identifies the type of view to create. The run-time class information and the current document pointer are used to create a new view dynamically. The following table suggests how and when each CCreateContext member might be used:

Member	What it is for
m_pNewViewClass	CRuntimeClass of the new view to create.
m_pCurrentDoc	The existing document to be associated with the new view.
m_pNewDocTemplate	The document template associated with the creation of a new MDI frame window.
m_pLastView	The original view upon which additional views are modeled, as in the creation of a splitter window's views or the creation of a second view on a document.
m_pCurrentFrame	The frame window upon which additional frame windows are modeled, as in the creation of a second frame window on a document.

When a document template creates a document and its associated components, it validates the information stored in the CCreateContext structure. For example, a view should not be created for a nonexistent document.

Примечание.
All of the pointers in CCreateContext are optional and can be NULL if unspecified or unknown.

CCreateContext is used by the member functions listed under "See Also." Consult the descriptions of these functions for specific information if you plan to override them.

Here are a few general guidelines:

When passed as an argument for window creation, as in CWnd::Create, CFrameWnd::Create, and CFrameWnd::LoadFrame, the create context specifies what the new window should be connected to. For most windows, the entire structure is optional and a NULL pointer can be passed.
For overridable member functions, such as CFrameWnd::OnCreateClient, the CCreateContext argument is optional.
For member functions involved in view creation, you must provide enough information to create the view. For example, for the first view in a splitter window, you must supply the view class information and the current document.

In general, if you use the framework defaults, you can ignore CCreateContext. If you attempt more advanced modifications, the Microsoft Foundation Class Library source code or the sample programs, such as VIEWEX, will guide you. If you do forget a required parameter, a framework assertion will tell you what you forgot.

For more information on CCreateContext, see the MFC sample VIEWEX.