Scrolling Alternatives The CscrollView class supports a particular kind of scrolling that involves one big window and a small viewport. Each item is assigned a unique position in this big window. If, for example, you have 10,000 address lines to display, instead of having a window 10,000 lines long, you probably want a smaller window with scrolling logic that selects only as many lines as the screen can display. In that case, you should write your own scrolling view class derived from Cview. The OnInitialUpdate Function you'll be seeing more of the OnInitialupdate function when you study the document-view architecture, starting in Chapter 15. The virtual OnInitialUpdate function is important here because it is the first function called by the framework after your view window is fully created. The framework calls OnInitialUpdate before it Calls OnDraw for the First Time, So OnInitialupdate Is The Natural Place for Setting The Logical Size and maping mode for a scrolling view. you set t HESE Parameters with a call to the cscrollview ::
SetScrollSizes function. Accepting Keyboard Input Keyboard input is really a two-step process. Windows sends WM_KEYDOWN and WM_KEYUP message, with virtual key codes, to a window, but before they get to the window they are translated. If an ANSI character is typed ( resulting in a WM_KEYDOWN message), the translation function checks the keyboard shift status and then sends a WM_CHAR message with the proper code, either uppercase or lowercase. Cursor keys and function keys do not have codes, so there's no translation to do. The . window gets only the WM_KEYDOWN and WM_KEYUP messages you can use the Class View's Properties window to map all these messages to your view If you're expecting characters, map WM_CHAR;. if you're expecting other keystrokes, map WM_KEYDOWN The MFC library. Neatly Supplies The Character Code or Virtual Key Code As a Handler Function Parameter. Select the scroll bar CScrollView class Support several special scroll bars including a large window and a small viewport. Each member assigns a location in a big window. For example, You have a 10,000-row address to display, you probably want to use the scroll to select a small window with the number of rows as the screen size, instead of a 100,000 row. In this example In, you will use it from the CView class to write your own scroll view class. The cursor keys and function keys are not encoded, so there is no need to switch jobs here. The window only wsm_keydown and wm_keyup messages. OnInitialUpdate functions from Chapter 15 Start, when you learn the document - view architecture, you will see a lot of oninitialupdate functions .onInitialUpdate is a virtual function, it is very important because it is a function that is called after your view is established. The frame will call the onDraw function before calling OnNitialUpdate, so OnInitialUpdate is the best setting logic size and scroll view mode. You want to set these parameters to call the cscrollview :: setScrollsizes function. Accept the keyboard Enter the keyboard Enter the actual It is a two-step process .Windows sends WM_KEYDOWN and WM_KEYUP messages, uses a virtual keyboard code to give a window, but they want to convert before giving the window. If it is an ASI type character (result in the WM_KeyDown message), conversion The function checks the SHIFT status of the keyboard and then sends a WM_CHAR message using the correct encoding. No casement, the cursor keys, and the function key are not encoded, so there is no need to conversion work. The window only gets WM_KeyDown and WM_KEYUP messages. You can use properties Class view window to map all of these messages to you. If you need characters, map WM_CHAR;
If you need other buttons, mapping WM_KEYDOWN.MFC perfect support characters and virtual keys are the same as the processing function parameters. The EX05C EXAMPLE: Scrolling The Goal of EX05C Is To Make A Logical Window 20 CENTIMETERS WIDE BY 30 CENTIMETERS HIGH. THE PROGRAM draws the same ellipse that it drew in the Ex05b project. You could edit the Ex05b source files to convert the Cview base class to a CscrollView base class, but it's easier to start over with the MFC Application Wizard. The wizard generates the OnInitialUpdate override function . for you Here are the steps: 1. Run the MFC Application Wizard to create Ex05c Use the wizard to generate an SDI program named Ex05c in the / vcppnet subdirectory Set the Cex05cView base class to CscrollView, as shown here:.. 2. Add the m_rectEllipse and m_nColor data members in Ex05cView.h Insert the following code using the Add Member Variable Wizard available from the class View's Properties window or by typing inside the Cex05cView class declaration: Private:. CRect m_rectEllipse; Int m_nColor; These are the same data MEMBERS THAT were added in the Ex05a and Ex05b projects 3. Modify the MFC Application Wizard-generated OnInitialUpdate function.Edit OnInitialUpdate in Ex05cView.cpp as shown here:. Void Cex05cView :: OnInitialUpdate () {CscrollView :: OnInitialUpdate (); Csize sizeTotal (20000 , 30000); // 20 by 30 cm csize sizepage (sizeetotal.cx / 2 ,ssotital.cy / 2); csize sizeeline (sizeetotal.cx / 50 ,stototal.cy / 50); setscrollsizes (mm_himetric, sizetotal, sizepage, Sizeline);
} 4. Use the Class View's Properties window to add a message handler for the WM_KEYDOWN message.The code wizards available from the Properties window generate the member function OnKeyDown along with the necessary message map entries and prototypes Edit the code as follows:. Void Cex05cView :: onkeydown (uint nchar, uint nrepcnt, uint nflags) {switch (nchar) {copy vk_home: Onvsroll (SB_TOP, 0, NULL); OnHSroll (SB_LEFT, 0, NULL); Break; Case VK_END: ONVSROLL (SB_BOTTOM, 0 , NULL); OnHSroll (SB_RIGHT, 0, NULL); Break; Case VK_UP: OnVScroll (SB_LINEUP, 0, NULL); Break; Case VK_DOWN: OnVScroll (SB_LINEDOWN, 0, NULL); Break; Case VK_PRIOR: OnVScroll (SB_PAGEUP, 0, NULL); Break; Case VK_NEXT: OnVScroll (SB_PAGEDOWN, 0, NULL); Break; Case VK_LEFT: OnVHcroll (SB_LINELEFT, 0, NULL); break; case VK_RIGHT: OnVHcroll (SB_LINERIGHT, 0, NULL); Break; Default : Break;}} 5. Edit the constructor and the onDraw function. Change The MFC Application Wizard-generated constructor and the onDraw function in EX05CVIEW.CPP As Follows: CEX05C View :: Cex05cView (): m_rectEllipse (0,0,4000, -4000) {m_nColor = GRAY_BRUSH;} void Cex05cView :: OnDraw (CDC * pDC) {pDC -> SelectStockObject (m_nColor); pDC -> Ellipse (m_rectEllipse) ;} These functions are identical to those used in the Ex05a and Ex05b projects 6. Map the WM_LBUTTONDOWN message and edit the handler Make the following changes to the generated code:.. Void Cex05cView :: OnLButtonDown (UINT nFlags, Cpoint point) {CClientDC dc (this); OnPrepareDC (& dc); CRect rectDevice = m_rectEllipse; dc.LPtoDP (rectDevice); if (rectDevice.PtInRect (point)) {if (m_nColor == GRAY_BRUSH) {m_nColor = WHITE_BRUSH;} else {m_nColor == Gray_brush);} invalidateRect (RectDevice);
}} This function is identical to the OnLButtonDown handler in the Ex05b project. It calls OnPrepareDC as before, but something is different. The Cex05bView class does not have an overridden OnPrepareDC function, so the call goes to CscrollView :: OnPrepareDC.That function sets the mapping mode based on the first parameter to SetScrollSizes, and it sets the window origin based on the current scroll position. Even if you scroll view were to user the MM_TEXT mapping mode, you'd still need the coordinate conversion logic to adjust for .. the origin offset 7. Build and run the Ex05c program Check to be sure that the mouse hit logic is working even if the circle is scrolled partially out of the window Also check the keyboard logic The output should look like this:.. examples EX05C: The purpose of scrolling this example is to create a 20 cm x30 cm window and draw the same ellipse as the EX05B project. You can convert to the CScrollView base class by modifying the EX05B source file CVIEW base class, but you use the MFC application to guide More easier. The wizard generates an OnInitialUpdate overload function. The following is the steps: 1. Run the MFC Application Wizard to establish an EX05C. Use the Wizard to create an SDI program named EX05C in / vcppnet subdirectory. Set the CEX05cView base class as CScrollView ,As shown below : 2. Increase M_Rectellipse and M_NColor variables into EX05CVIEW.H. Increase the data variable wizard from the Properties window of the class view, insert the following code or type code in the CEX05cView class definition: private: CRECT M_RECTELLIPSE; int m_ncolor; these data members with EX05A As in the EX05B project. 3. Modify the OnInitialUpdate function generated by the MFC Application Wizard. Edit the OnInitialUpdate function in EX05CVIEW.CPP, as shown below: Void Cex05cview :: OnInitialUpdate () {cscrollview :: onInitialUpdate (); csize sizetotal 20000, 30000); // 20 by 30 cm csize sizepage (siz / 2); csize sizeeline (sizel.cx / 50 ,stotital.cy / 50); setscrollsizes (mm_himetric, sizetotal, sizepage , Sizeline);} 4. Add message processing to WM_KEYDOWN messages using the attribute window of the class view. Use the code wizard from the property window to generate the onkeydown function and the necessary message mapping portal and original shape. Edit the following code: void CEX05CVIEW :: onkeyDown Uint nchar, uint nrepcnt, uint nflags) {switch (nchar) {copy vk_home: ONVSROLL (SB_TOP, 0, NULL); onhsroll (SB_LEFT, 0, NULL); BREAK;
Case VK_END: OnVSroll (SB_BOTTOM, 0, NULL); OnHSroll (SB_RIGHT, 0, NULL); Break; Case VK_UP: OnVScroll (SB_LINEUP, 0, NULL); Break; Case VK_DOWN: OnVScroll (SB_LINEDOWN, 0, NULL); Break ; Case VK_PRIOR: OnVScroll (SB_PAGEUP, 0, NULL); Break; Case VK_NEXT: OnVScroll (SB_PAGEDOWN, 0, NULL); Break; Case VK_LEFT: OnVHcroll (SB_LINELEFT, 0, NULL); break; case VK_RIGHT: OnVHcroll (SB_LINERIGHT, 0, NULL); Break; default: Break;}} 5. Modify the constructor and the onDraw function. Change the constructor generated in the EX05cView.cpp file generated by the MFC application wizard with the following code CEX05CView :: CEX05CVIEW (): m_rectEllipse (0,0,4000, -4000) {m_nColor = GRAY_BRUSH;} void Cex05cView :: OnDraw (CDC * pDC) {pDC -> SelectStockObject (m_nColor); pDC -> Ellipse (m_rectEllipse);} and these functions Ex05a .. Ex05b likewise be used and 6. the map editing process WM_LBUTTONDOWN message changing codes generated following arrangements: Void Cex05cView :: OnLButtonDown (UINT nFlags, Cpoint point) {CClientDC dc (this); OnPrepareDC (& dc); CRect rectDevice = m_rectEllipse Dc.lptodp (RectDevice); if (RectDevice.ptinRect (POINT)) {if (m_ncolor == gray_brush) {m_ncolor = white_brush;} else {m_ncolor == gray_brush);} InvalidateRec T (RectDevice);
}} This online ONLBUTTONDOWN is also processed in the EX05b project. It is called before calling OnPreParedc, but sometimes different. CEX05BVIEW classes cannot be overloaded overpreparedc functions, so to call the cscrollview :: onpreparedc.setscrollsize function The parameter is to set the mapping mode. It also sets the origin of the window according to the current scroll coordinates. Even if your scroll view uses mm_text mapping mode, you still need to convert logical coordinates and adjust the origin shift. 7. Generate and run EX05C Program. Check that when the circle is partially scrolled outside to the window, the mouse click still effectively also uses a keyboard test. The output program is shown below: USING OTHER Windows Messages The MFC Library Directly Supports Hundreds of Windows Message-Handling functions. in addition, you can define your own messages you'll see plenty of message-handling examples in later chapters, including handlers for menu items, child window controls, and so forth in the meantime, five special Windows messages deserve special attention..: WM_CREATE, WM_CLOSE, WM_QUERYENDSESSION, WM_DESTROY, and WM_NCDESTROY. The WM_CREATE Message This is the first message that Windows sends to a view. It is sent when the window's Create function is called by the framework. At that time, the window creation is not finished , So the window is not visible. Therefore, Your Oncrecte Handler Cannot Cal l Windows functions that depend on the window being completely alive. You can call such functions in an overridden OnInitialUpdate function, but you must be aware that in an SDI application OnInitialUpdate can be called more than once in a view's lifetime. using other Windows messages MFC The library supports hundreds of Windows message processing functions. In addition, you can first belong to your own message. You will see a lot of message processing in the later chapter, including menu processing, sub-window control, and more. In this whole, there are five special Windows messages should pay special attention:
WM_CREATE, WM_CLOSE, WM_QUERYENDSESSION, WM_QUERYENDSESSION, WM_DESTROY, and WM_NCDESTROY. WM_CREATE Message This message is Windows first sends a message. Send it when the frame calls the window's Create function. At that time, the window is not established, it is not visible. So Your oncreate function cannot call the Windows function that it requires a complete activity. You can call such a function in the overnosis in ONInitialUpdate, but you must understand that OnInitialUpdate will not only understand in a view of an SDI application. one is called. the WM_CLOSE Message Windows sends the WM_CLOSE message when the user closes a window from the system menu and when a parent window is closed. If you implement the OnClose message map function in your derived view class, you can control the closing process. If, for example, you need to prompt the user to save changes to a file, you can do it in OnClose. Only after you've determined that it is safe to close the window should you call the base class OnClose function, which will continue the close process. The view object and the corresponding window will both still be active. Note When you're using the full application framework, you probably will not use the WM_CLOSE message handler. you can override the Cdocument ::
SaveModified virtual function instead, as part of the application framework's highly structured program exit procedure. The WM_QUERYENDSESSION Message Windows sends the WM_QUERYENDSESSION message to all running application when the user exits Windows. The OnQueryEndSession message map function handles it. If you write a handler for WM_CLOSE , you should write one for WM_QUERYENDSESSION, too. The WM_DESTROY Message Windows sends the WM_DESTROY message after the WM_CLOSE message, and the OnDestroy message map function handles it. When your program receives this message, it should assume that the view window is no longer visible on the screen but that it is still active and its child windows are still active. You use this message handler to do cleanup that depends on the existence of the underlying window. Be sure to call the base class OnDestroy function. You can not "abort" THE WINDOW DESTRUCTION PROCESS IN YOUR VIEW's OnDestroy Function. Onclose Is The Place To Do T. The WM_NCDESTROY Message This is the last message that Windows sends when the window is being destroyed. All child windows have already been destroyed. You can do final processing in OnNcDestroy that does not depend on a window being active. Be sure to call the base class OnNcDestroy function. Note Do not try to destroy a dynamically allocated window object in OnNcDestroy. that job is reserved for a special CWnd virtual function, PostNcDestroy, that the base class OnNcDestroy calls. MFC Technical Note # 17 in the online documentation offers hints about when it's ApproPriate to Destroy A Window Object.
