各位大虾,小弟初学VC,有谁能指点一下定时器的作用?谢谢!
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The following example uses the SetTimer function to create two timers. The first timer is set for every 10 seconds, the second for every 5 minutes. // Set two timers.
SetTimer(hwnd, // handle to main window
IDT_TIMER1, // timer identifier
10000, // 10-second interval
(TIMERPROC) NULL); // no timer callback
SetTimer(hwnd, // handle to main window
IDT_TIMER2, // timer identifier
300000, // 5-minute interval
(TIMERPROC) NULL); // no timer callback
To process the WM_TIMER messages generated by these timers, add a WM_TIMER case statement to the window procedure for the hwnd parameter. case WM_TIMER:
switch (wParam)
{
case IDT_TIMER1:
// Process the 10-second timer.
return 0;
case IDT_TIMER2:
// Process the 5-minute timer. return 0;
}
An application can also create a timer whose WM_TIMER messages are processed not by the main window procedure but by an application-defined callback function, as in the following code sample, which creates a timer and uses the callback function MyTimerProc to process the timer's WM_TIMER messages. // Set the timer.
SetTimer(hwnd, // handle to main window
IDT_TIMER3, // timer identifier
5000, // 5-second interval
(TIMERPROC) MyTimerProc); // timer callback
The calling convention for MyTimerProc must be based on the TimerProc callback function. If your application creates a timer without specifying a window handle, your application must monitor the message queue for WM_TIMER messages and dispatch them to the appropriate window. Note that GetMessage can return -1 if there is an error.HWND hwndTimer; // handle to window for timer messages
MSG msg; // message structure
while (GetMessage(&msg, // message structure
NULL, // handle to window to receive the message
NULL, // lowest message to examine
NULL) // highest message to examine
!= 0 && GetMessage(&msg, NULL, NULL, NULL) != -1)
{
// Post WM_TIMER messages to the hwndTimer procedure.
if (msg.message == WM_TIMER)
{
msg.hwnd = hwndTimer;
}
TranslateMessage(&msg); // translates virtual-key codes
DispatchMessage(&msg); // dispatches message to window
}
Sometimes it is necessary to prevent more input while you have a cursor on the screen. One way to accomplish this is to create a special routine that traps mouse input until a specific event occurs. Many developers refer to this routine as "building a mousetrap." The following example uses the SetTimer and KillTimer functions to create a simple mousetrap. SetTimer creates a timer that sends a WM_TIMER message every 10 seconds. Each time the application receives a WM_TIMER message, it records the cursor location. If the current location is the same as the previous location and the application's main window is minimized, the application moves the cursor to the icon. When the application closes, KillTimer stops the timer. HICON hIcon1; // icon handle
POINT ptOld; // previous cursor location
UINT uResult; // SetTimer's return value
HINSTANCE hinstance; // handle to current instance
//
// Perform application initialization here.
//
wc.hIcon = LoadIcon(hinstance, MAKEINTRESOURCE(400));
wc.hCursor = LoadCursor(hinstance, MAKEINTRESOURCE(200));
// Record the initial cursor position.
GetCursorPos(&ptOld);
// Set the timer for the mousetrap.
uResult = SetTimer(hwnd, // handle to main window
IDT_MOUSETRAP, // timer identifier
10000, // 10-second interval
(TIMERPROC) NULL); // no timer callback
if (uResult == 0)
{
ErrorHandler("No timer is available.");
}
LONG APIENTRY MainWndProc(
HWND hwnd, // handle to main window
UINT message, // type of message
WPARAM wParam, // additional information
LPARAM lParam) // additional information
{
HDC hdc; // handle to device context
POINT pt; // current cursor location
RECT rc; // location of minimized window
switch (message)
{
//
// Process other messages.
//
case WM_TIMER:
// If the window is minimized, compare the current
// cursor position with the one from 10 seconds
// earlier. If the cursor position has not changed,
// move the cursor to the icon.
if (IsIconic(hwnd))
{
GetCursorPos(&pt);
if ((pt.x == ptOld.x) && (pt.y == ptOld.y))
{
GetWindowRect(hwnd, &rc);
SetCursorPos(rc.left, rc.top);
}
else
{
ptOld.x = pt.x;
ptOld.y = pt.y;
}
}
return 0;
case WM_DESTROY:
// Destroy the timer.
KillTimer(hwnd, IDT_MOUSETRAP);
PostQuitMessage(0);
break;
//
// Process other messages.
//
}
Although the following example also creates a mousetrap, it processes the WM_TIMER message through the application-defined callback function MyTimerProc, rather than through the application's message queue. UINT uResult; // SetTimer's return value
HICON hIcon1; // icon handle
POINT ptOld; // previous cursor location
HINSTANCE hinstance; // handle to current instance
//
// Perform application initialization here.
//
wc.hIcon = LoadIcon(hinstance, MAKEINTRESOURCE(400));
wc.hCursor = LoadCursor(hinstance, MAKEINTRESOURCE(200));
// Record the current cursor position.
GetCursorPos(&ptOld);
// Set the timer for the mousetrap.
uResult = SetTimer(hwnd, // handle to main window
IDT_MOUSETRAP, // timer identifier
10000, // 10-second interval
(TIMERPROC) MyTimerProc); // timer callback
if (uResult == 0)
{
ErrorHandler("No timer is available.");
}
LONG APIENTRY MainWndProc(
HWND hwnd, // handle to main window
UINT message, // type of message
WPARAM wParam, // additional information
LPARAM lParam) // additional information
{
HDC hdc; // handle to device context
switch (message)
{
//
// Process other messages.
//
case WM_DESTROY:
// Destroy the timer.
KillTimer(hwnd, IDT_MOUSETRAP);
PostQuitMessage(0);
break;
//
// Process other messages.
//
}
// MyTimerProc is an application-defined callback function that
// processes WM_TIMER messages.
VOID CALLBACK MyTimerProc(
HWND hwnd, // handle to window for timer messages
UINT message, // WM_TIMER message
UINT idTimer, // timer identifier
DWORD dwTime) // current system time
{
RECT rc;
POINT pt;
// If the window is minimized, compare the current
// cursor position with the one from 10 seconds earlier.
// If the cursor position has not changed, move the
// cursor to the icon.
if (IsIconic(hwnd))
{
GetCursorPos(&pt);
if ((pt.x == ptOld.x) && (pt.y == ptOld.y))
{
GetWindowRect(hwnd, &rc);
SetCursorPos(rc.left, rc.top);
}
else
{
ptOld.x = pt.x;
ptOld.y = pt.y;
}
}
}