Signals and slots are used for communication between objects. The signals and slots mechanism is a central feature of Qt and probably the part that differs most from the features provided by other frameworks.
In GUI programming, when we ...
标准 C++ 对象模型为对象范式，提供了非常有效的运行时支持。但其静态性质在某些问题领域是不灵活的。GUI (图形用户界面) 编程要求运行时高效，且高级灵活性的两者领域。Qt 通过组合 C++ 的速度与 Qt 对象模型的灵活性，提供这。
The Qt layout system provides a simple and powerful way of specifying the layout of child widgets.
By specifying the logical layout once, you get the following benefits:
