由于回收之后存留下来的物件通常具有较长的存留期，因此才会将它们提升至较高的层代。

Because objects that survive collections tend to have longer lifetimes, it makes sense to promote them to a higher generation.

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WPF有四种主要的物件类型与存留期事件相关，分别是一般项目、视窗项目、巡览装载和应用程序物件。

There are four main types of objects in WPF with respect to lifetime events; elements in general, window elements, navigation hosts, and application objects.

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