\nA customer reported that their taskbar would sometimes\nspontaneously go into auto-hide mode.\nWhat made this particularly insidious was that they\nhad deployed a group policy to\nprevent users from changing the auto-hide state\n(because they never wanted the taskbar to auto-hide),\nso when the taskbar went into auto-hide mode,\nthere was no way to get it out of that mode!\n<\/p>\n
\nThe customer’s first investigation was to find out\nwhere the auto-hide state was recorded.\nA little bit of registry spelunking\n(because as far as these people are concerned,\neverything<\/i> is in the registry)\nshowed that a single bit in the\n \nIt turns out that watching the registry value get updated\ndoesn’t tell you anything interesting.\nExplorer always writes that value when you log off,\nand the value written is the taskbar’s current auto-hide state.\nThe real culprit is the person who changed<\/i> the taskbar’s state,\ncausing Explorer to save the updated state at logoff.\nAnd that culprit is somebody who called\n \nI warned you many years ago that\n\nthe auto-hide and always-on-top\nstates are user settings<\/a>,\nand programs should modify them only under the instructions of the user.\n<\/p>\n \nThe support technician was able to put together an\ninstrumented version of the\n \nA few days later, the support technician reported back:\nThe culprit was found with his hand in the cookie jar!\nOne of the applications the customer was using was indeed calling\n \nMind you, even if the application remember to set the auto-hide flag\nback to its original value, that still wouldn’t have been the correct\nsolution.\n\nSuppose two programs did this<\/a>.\n<\/p>\n \nThe user first runs the other program, which remembers that the taskbar\nis not auto-hide, then sets it to auto-hide.\nNow the user runs your program, which remembers that the taskbar is\nauto-hide, and then sets the taskbar (redundantly) to auto-hide.\nThe user exits the first program, which sets the taskbar to normal.\nNow the taskbar is in normal state even though the your program wants\nit to be auto-hide.\nFinally, your program exits, and it “restores” the taskbar to auto-hide.\n<\/p>\n \nThis is just\nanother case of\n\nusing a global setting to solve a local problem<\/a>.\nThe local solution is to\n\ncreate a fullscreen window<\/a>,\nand the taskbar will get out of the way automatically.\n<\/p>\n \nThe customer went to the online support forum for the program that was\nsetting the taskbar to auto-hide and forgetting to restore it.\nAnd, how about that,\nthere was a thread in that forum called something like\n“After I run Program X, my taskbar gets set to auto-hide.”\n<\/p>\nStuckRects2<\/code> registry value controlled\nthe auto-hide setting.\nThey used\n\nProcess Monitor<\/a>\nand observed that it was Explorer that was updating the value.\nThat was as far as they could troubleshoot the problem\nand came to the Windows team for further guidance.\n<\/p>\nSHAppBarMessage<\/code> with the\nABM_SETSTATE<\/code> parameter,\nin order to turn on the ABS_AUTOHIDE<\/code> bit.\n<\/p>\nSHAppBarMessage<\/code> function\nthat logged any attempt to put the taskbar into auto-hide mode.\n(This step took a little while because the first attempt wasn’t\nquite right and ended up not working.)\n<\/p>\nSHAppBarMessage<\/code> with the\nABM_SETSTATE<\/code> parameter,\nand passing the\nABS_AUTOHIDE<\/code> flag to make the taskbar auto-hide,\nand the application never called the function again to restore\nit back to normal.\nResult:\nTaskbar goes to auto-hide and stays there.\n<\/p>\n\nbool fWasTaskbarAutoHide;\nOnStartup()\n{\n fWasTaskbarAutoHide = GetTaskbarAutoHideState();\n SetTaskbarAutoHide(true);\n}\nOnExit()\n{\n SetTaskbarAutoHide(fWasTaskbarAutoHide);\n}\n<\/pre>\n