关于Windows消息的一个简单问题。

[sadpacific]

Delphi中定义了一个常量HWND_BROADCAST，谁能够告诉我这个常量有什么作用？
能否举个例子？

[hubdog]

sendmessage(hwnd_broadcast,wm_keydown,0,0);
就是给“所有”的窗口发消息时用的常量
给某一个窗口发消息常是sendmessage(onewinhandle,wm_keydown,0,0);

[forgettor]

通常是通知系统中某些全局信息发生变化的，例如屏幕分辨率发生了变化等

[sadpacific]

To all:
执行下面一行代码
PostMessage(HWND_BROADCAST, WM_SYSCOMMAND, SC_SCREENSAVE, 0);
我发现当前有几个窗口，则系统就会启动几个屏保，请问这是怎么会事？

[kxy]

windows API的帮助中看SendMessage的帮助，
LRESULT SendMessage(

HWND hWnd, // handle of destination window
UINT Msg, // message to send
WPARAM wParam, // first message parameter
LPARAM lParam // second message parameter
);
Parameters

hWnd

Identifies the window whose window procedure will receive the message. If this parameter is HWND_BROADCAST, the message is sent to all top-level windows in the system, including disabled or invisible unowned windows, overlapped windows, and pop-up windows; but the message is not sent to child windows.
如果hWnd是HWND_BROADCAST, 这条消息将发给所有的 top-level窗口，包括失效的和
隐藏，overlapped和pop-up 但是不包括子窗口

[kxy]

自然会启动n个屏保，请多看help:)