本代码制作计算器。执行本例实例后，将创建一个计算器，可以进行常用的加减乘除算术运算。本实例的知识点有：窗口布局器GridLayout的应用，对按钮消息的监听和响应 。-The code produced calculator. Examples of the implementation of this case, it will create a calculator that can be commonly used arithmetic operations addition and su