控件状态11种，必须倒背如流——记录控件当前的状态，防止误判（一般使用完以后就把状态改回去）

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：