Using SystemParametersInfo to access user interface settings
The SystemParametersInfo function
gives you access to a whole slew of user interface settings,
and it is the only supported method for changing those settings.
I'm not going to list every single setting; go read the list yourself.
Here are some highlights:
- SPI_GETICONTITLELOGFONT lets you query the font that is used for
icon labels; SPI_SETICONTITLELOGFONT lets you change it.
- SPI_GETNONCLIENTMETRICS lets you query the fonts that are used for
window captions, menus, status bars, and message boxes;
SPI_SETNONCLIENTMETRICS lets you change them.
Here are some control panel settings.
- SPI_SETKEYBOARDDELAY and SPI_SETKEYBOARDSPEED let you set the
keyboard autorepeat parameters.
- SPI_SETDOUBLECLICKTIME lets you set the
mouse double-click speed.
- SPI_SETMENUFADE lets you enable or disable the
menu fade animation. [Typo fixed, 4pm.]
- There is a whole series of SPI_SETxxxANIMATION settings
that let you control which screen elements animate.
Notice that when using the SPI_SET* commands,
you also have to choose whether the setting changes are
temporary (lost at logoff) or persistent.
The historically-named SPIF_UPDATEINIFILE flag
causes the changes to be saved to the user profile; if you
leave it off, then the changes are not saved and are lost
when the user logs off.
You should also set the SPIF_SENDCHANGE flag so
that programs which want to refresh themselves in response to
changes in the settings can do so.
The fact that there exist both temporary and persistent changes
highlights the danger of accessing the registry directly
to read or write the current settings. If the current settings are
temporary, then they are not saved in the registry.
The SystemParametersInfo function retrieves the
actual current settings, including temporary ones.
For example, if you want to query whether menus are being animated,
and the user has temporarily disabled animation, reading the registry
will tell you that they are being animated when
in fact they are not.
Also, changes written to the registry don't take effect untll the
next logon, because that is the only time the values are consulted.
To make a change take effect immediately, you must use
SystemParametersInfo.
It still puzzles me why people go to the undocumented registry keys
to change these settings
when there is a perfectly good documented function for doing it.
Especially when the documented function works and the
undocumented registry key is unreliable.
I remember one application that went straight for the undocumented
registry keys (to get the icon title font, I think).
Unfortunately for the application, the format of the registry key
is different between Windows 95 and Windows 2000,
and it ended up crashing. (It expected the Windows 95 format.)
If it had used the documented method
of retrieving the icon title font, it would have worked fine.
In other words, this program went out of its way to go around
the preferred way of doing something and got hoist by its own petard.
