TControlState = set of (csLButtonDown, csClicked, csPalette,
csReadingState, csAlignmentNeeded, csFocusing, csCreating,
csPaintCopy, csCustomPaint, csDestroyingHandle, csDocking);
http://www.cnblogs.com/huangjacky/archive/2010/02/26/1674621.html
http://www.cnblogs.com/huangjacky/archive/2010/03/03/1677087.html
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举例说明：