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This information in this article applies to:
The Microsoft Foundation Classes (MFC) included with:
- Microsoft Visual C++ for Windows, versions 1.0, 1.5, 1.51 1.52
- Microsoft Visual C++, 32-bit Edition, versions 2.0, 2.1, 4.0, 5.0
SUMMARY
The text below describes a process by which a MFC AppWizard application can
be designed to display the current time on its status bar.
Perform the following five steps:
- Use App Studio, or the Resource View in Visual C++ versions later than
4.0, to edit the application's string tables. Add a new string in the
segment that defines ID_INDICATOR_NUM and so on; for example, create a
new string with the ID ID_INDICATOR_TIME. Specify a caption like 00:00.
The Status Bar uses the specified initial value to calculate the size
of the pane. An application can dynamically change the size of the
pane using the CStatusBar::SetPaneInfo() function. With Visual C++
versions prior to 4.0, close App Studio to save the .RC file. With
Visual C++ version 4.0 or later, use the File menu to Save and Close the
string table resource.
- Edit the MAINFRM.CPP file. The CStatusBar object builds the status
bar using the data in the indicators[] array in sequential order.
Insert the ID_INDICATOR_TIME indicator into the array at the
desired position.
If you compiled the program at this stage, you would see a new pane
in the status bar but it would not contain any text.
- Edit the message map for the CMainFrame object to add the following
line (add the line outside the AFX_MSG_MAP comments):
ON_UPDATE_COMMAND_UI(ID_INDICATOR_TIME, OnUpdateTime)
Because ID_INDICATOR_TIME is an ID, and not an object, you cannot
use Class Wizard to make this addition.
- Edit the MAINFRM.CPP file and create a function similar to the
following:
void CMainFrame::OnUpdateTime(CCmdUI *pCmdUI)
{
CTime t = CTime::GetCurrentTime();
char szTime[6];
int nHour = t.GetHour();
int nMinute = t.GetMinute();
// Base Hours on 12 instead of 24
if (nHour > 12)
nHour = nHour - 12;
wsprintf(szTime, "%i:%02i", nHour, nMinute);
// Now set the text of the pane.
m_wndStatusBar.SetPaneText(
m_wndStatusBar.CommandToIndex(ID_INDICATOR_TIME),
LPCSTR(szTime));
pCmdUI->Enable();
}
The application calls this function once when it has idle time.
Each time the application empties its message queue, it sends a
WM_IDLEUPDATECMDUI message (new idle time). For more information on
idle time, please refer to Technical Note #24 in the MFC Tech Notes
help file or to the documentation of the CWinApp::OnIdle() function
in the "Class Library Reference, Volume 1." The application must
call the pCmdUI->Enable() function to enable the user-interface
item for this command. If the application doesn't enable the
user-interface item, the pane appears in the status bar, but it
does not display any text.
If you compiled the program at this point, the status bar would
display the current time in one of its panes. However, one
implementation problem would remain. Because the application calls
the UI Command Handler only once each time the system becomes idle,
what happens if the application runs and the user does not interact
with it? The application does not reset the time until it receives
one or more messages and empties its queue (new idle time). The
code in Step 5 addresses this situation.
- Even though there are several methods to accomplish this, the
simplest method takes advantage of the fact that the application
calls the UI Command Handler only once when the application's
message queue is emptied. Add the following statement to the
CMainFrame::OnCreate() member function:
m_wndStatusBar.SetTimer(1, 1000, NULL);
The CWnd::SetTimer() event generates a message in the application's
queue every second. Even if the user does not interact with the
application, the queue empties after processing the timer event,
new idle time is available, and the application updates the time
pane in its status bar. Be sure to call KillTimer() when the window is
destroyed.
MORE INFORMATION
When a modal dialog box is up, the dialog manager manages the application's
message queue. Since the dialog manager's message loop does not include
calls to do Idle time processing, the above mentioned OnUpdateTime function
never gets called. If you would like to use a modal dialog, yet still have
the time on the status bar updated, you will have to avoid using the
message queue.
- Start with the code above.
- In mainfrm.h, add the following to the CMainFrame class definition.
UINT m_nIDTimer;
static VOID __export CALLBACK TimerProc(HWND hwnd, UINT uMsg,
UINT uIDEvent, DWORD dwTime);
NOTE: In Win32, the "__export" keyword is obsolete and will cause the
compiler to generate a C4236 warnings in Visual C++ version 4.0 or
later. To correct, simply remove the keyword.
- In mainfrm.cpp, change the SetTimer() call in CMainFrame::OnCreate() to:
m_nIDTimer = ::SetTimer(NULL, 0, 1000, TimerProc);
- Add a timer procedure:
VOID __export CALLBACK CMainFrame::TimerProc(HWND hwnd, UINT uMsg,
UINT uIDEvent, DWORD dwTime)
{
CMainFrame *pMainWnd = (CMainFrame *)AfxGetApp()->m_pMainWnd;
ASSERT(uIDEvent == pMainWnd->m_nIDTimer);
CCmdUI cui;
cui.m_nID = ID_INDICATOR_TIME;
cui.m_nIndex = 4;
cui.m_pMenu = NULL;
cui.m_pOther = &pMainWnd->m_wndStatusBar;
pMainWnd->OnUpdateTime(&cui);
}
- In the destructor, use:
::KillTimer(NULL, m_nIDTimer);
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