statusTip : QString
This property holds the widget's status tip.
By default, this property contains an empty string.
toolTip : QString
This property holds the widget's tooltip.
Note that by default tooltips are only shown for widgets that are children of the active window. You can change this behavior by setting the attribute Qt::WA_AlwaysShowToolTips on the window, not on the widget with the tooltip.
If you want to control a tooltip's behavior, you can intercept the event() function and catch the QEvent::ToolTip event (e.g., if you want to customize the area for which the tooltip should be shown).
By default, this property contains an empty string.
whatsThis : QString
This property holds the widget's What's This help text.
By default, this property contains an empty string.
纠结，在看Qt文档的时候，感觉看了跟没看一样，还是不能怎么理解~
现在在用QComboBox，想实现鼠标移到QComboBox的时候就能在鼠标旁有一个文本框文字提示一下下，不过不知道用哪个Tip还是使用Event?
就我自己做过的，就只做过toolTip，我理解是这样的，toolTip设定了的时候会在状态栏那里显示。
然后另外两个就没有试过了，字面理解的话，第一个指定状态？第二个使用于帮助？
那如果我想实现上述功能的话，是要用第三个？
------解决方案--------------------
myWidget -> setStatusTip ("StatusTip");//状态栏提示
myWidget -> setToolTip ("ToolTip"); //鼠标放到控件上，浮动出一个小黄框。
myWidget -> setWhatsThis ("WhatsThis");//QDialog 标题栏上有一个？按钮，先点按钮鼠标变问号，再点控件。