ASP.net WebForms – 构造函数与Page_Load

你必须看看 asp.net life cycle.
在costructor方法上,您可以编写大量代码,声明变量以及使用类和库.
但是如果你需要一些asp.net元素(Page,Controls,Session,QueryString等),你需要在Page_Load或其他生命周期方法中.

When an ASP.NET page runs,the page goes through a life cycle in which it performs a series of processing steps. These include initialization,instantiating controls,restoring and maintaining state,running event handler code,and rendering. It is important for you to understand the page life cycle so that you can write code at the appropriate life-cycle stage for the effect you intend. Additionally,if you develop custom controls,you must be familiar with the page life cycle in order to correctly initialize controls,populate control properties with view-state data,and run any control behavior code. (The life cycle of a control is based on the page life cycle,but the page raises more events for a control than are available for an ASP.NET page alone.)