问题
My application draws all its own window borders and decorations. It works fine with Windows taskbars that are set to auto-hide, except when my application window is maximized. The taskbar won't "roll up". It will behave normally if I have the application not maximized, even when sized all the way to the bottom of the screen. It even works normally if I just resize the window to take up the entire display (as though it was maximized).
回答1:
I found the problem. My application was handling the WM_GETMINMAXINFO message, and was overriding the values in the parameter MINMAXINFO record. The values that were in the record were inflated by 7 (border width) the screen pixel resolution. That makes sense in that when maximized, it pushes the borders of the window beyond the visible part of the screen. It also set the ptMaxPosition (point that the window origin is set to when maximized) to -7, -7. My application was setting that to 0,0, and the max height and width to exactly the screen resolution size (not inflated). Not sure why this was done; it was written by a predecessor. If I comment out that code and don't modify the MINMAXINFO structure, the Auto-hide works.
As to why, I'm not entirely sure. It's possible that the detection for popping up an "autohidden" taskbar is hooked into the mechanism for handling WM_MOUSEMOVE messages, and not for WM_NCMOUSEMOVE. With my application causing the maximize to park my border right on the bottom of the screen, I would have been generating WM_NCMOUSEMOVE events; with the MINMAXINFO left alone, I would have been generating WM_MOUSEMOVE.
回答2:
This is dependant on whether 'Keep the taskbar on top of other windows' is checked on the taskbar properties. If it's checked then the taskbar will appear.
But don't be tempted to programmatically alter this setting on an end users machine just to suit your needs, it's considered rude and bad practice. Your app should fit whatever environment it gets deployed to.
来源：https://stackoverflow.com/questions/137005/auto-hide-taskbar-not-appearing-when-my-application-is-maximized