Question

VC++ OnCommand(WPARAM wParam, LPARAM lParam) 的问题

假如是一个动态按钮发送了这个消息，那么在这个消息函数中，参数lParam所指向的是什么？

Answer 1

OnCommand是WM_COMMAND消息的响应函数，我想你也知道，这个消息的wParam的低字是控件ID，lParam是发送这个WM_COMMAND消息的控件的句柄。
动态创建的按钮，和在资源文件里定义的按钮从本质上来说是没有区别的，只是资源文件里画出来的的按钮是由Windows在加载你的资源时，从PE文件的资源里读出、创建的，也属于“动态创建”的。
按钮控件的句柄。

Answer 2

来自MSDN的解释：

The framework calls this member function when the user selects an item from a menu, when a child control sends a notification message, or when an accelerator keystroke is translated.

virtual BOOL OnCommand(
WPARAM wParam,
LPARAM lParam
);

Parameters
wParam
The low-order word of wParam identifies the command ID of the menu item, control, or accelerator. The high-order word of wParam specifies the notification message if the message is from a control. If the message is from an accelerator, the high-order word is 1. If the message is from a menu, the high-order word is 0.

lParam
Identifies the control that sends the message if the message is from a control. Otherwise, lParam is 0.

Return Value
An application returns nonzero if it processes this message; otherwise 0.