WM_MDINEXT
wParam = (WPARAM) hwndChild; /* handle of child window */
lParam = (LPARAM) fNext; /* next or previous child window */
An application sends the WM_MDINEXT message to a multiple document interface (MDI) client window to activate the child window immediately behind the currently active child window and place the currently active child window behind all other child windows.
hwndChild
Value of wParam. Specifies the handle of the child window.
fNext
Value of lParam. If this parameter is zero, the message specifies that the next MDI child window should be activated. If this parameter is nonzero, the message specifies that the previous MDI child window should be activated.
An application should return zero if it processes this message.
If an MDI client window receives any message that changes the activation of its child windows while the currently active MDI child window is maximized, Windows restores the currently active child window and maximizes the newly activated child window.
WM_MDIACTIVATE, WM_MDIGETACTIVE