监视器数量变化时的通知是什么？

Question

I'm curious, what is the Win32 notification that is broadcast when the number of monitors in the system changes? I thought it was WM_DISPLAYCHANGE but I was wrong.

Answer 1

This is quite easy to check with Microsoft Spy++ . In my case I checked on Windows 7 x64 with two monitors connected and switching the second monitor off and on again.

When removing a monitor you will see a WM_DISPLAYCHANGE , but not when adding a monitor.

You will see a WM_DEVICECHANGE with DBT_DEVNODES_CHANGED (after RegisterDeviceNotification ).

You will see WM_SETTINGCHANGE for SPI_SETWORKAREA and SPI_ICONVERTICALSPACING .

And you will see registered messages "UxdDisplayChangeMessage" and "HotplugDetected" (second one only when adding monitor). You can use RegisterWindowMessage to get the identifier for these messages.