QT 5.1界面编程入门范例。Hello world。里面包含三个例子：1. 最简单的hello world程序；2. 添加退出按钮；3. 信号和槽的简单互动-QT 5.1 interface programming entry model. Hello world. Which contains three examples: 1. Most simple hello world program 2. Added eject button 3 simple interactive sign