c++ - 定时器超时复位

Question

我使用计时器绘制动画，但我希望动画的速度根据用户输入而改变。

关于 API's documentation ，我读到:

A handle to the window to be associated with the timer. This window must be owned by the calling thread. If a NULL value for hWnd is passed in along with an nIDEvent of an existing timer, that timer will be replaced in the same way that an existing non-NULL hWnd timer will be.

我知道我应该在没有 hWnd 参数的情况下调用 SetTimer() 函数来重置计时器，所以我这样做了:

//函数声明

void InitiateTimer(HWND hWnd)
{
    SetTimer(hWnd,                          // handle to main window 
        IDT_TIMER,                          // timer identifier 
        1000 / Robot_Settings::getSpeed(),  // 1-second interval / speed 
        (TIMERPROC)NULL);                   // no timer callback 

    timerInitiated = true;
}

void ResetTimer()
{
    SetTimer(NULL,
        IDT_TIMER, 
        1000 / Robot_Settings::getSpeed(), 
        (TIMERPROC)NULL);
}

//WindowProc中的函数调用

    case BUTTON_START:
        stopClicked = false;
        DestroyWindow(hStartButton);
        CreateStopButton(hWnd);
        if (!timerInitiated)
        {
            InitiateTimer(hWnd);
        }
        else if (timerInitiated)
        {
            ResetTimer();
        }
        return 0;

想法是在重置时，超时将根据 Robot_Settings::getSpeed() 重新计算。不幸的是，这不会发生。

我错过了什么？

Answer 1

我认为您误解了文档。

要更改现有计时器，您必须传递与最初调用时相同的 hWnd、nIDEvent 和 lpTimerFunc 参数组合 设置定时器。

来自reference :

If the hWnd parameter is not NULL and the window specified by hWnd already has a timer with the value nIDEvent, then the existing timer is replaced by the new timer.

还有:

The timer identifier, nIDEvent, is specific to the associated window. Another window can have its own timer which has the same identifier as a timer owned by another window. The timers are distinct.

仅最后一句话就足以证明您始终必须指定 hWnd 参数来修改与窗口关联的现有计时器。否则，系统怎么知道，你想改变哪个定时器？您可以有两个窗口，每个窗口的计时器 ID 为 1，这是两个不同的计时器!