Shouldn’t classes all be contained in their own files?

Android活动不一定是’特殊情况’类.如果你还没有,我建议你阅读Application Fundamentals,特别是Application components下的“活动”部分……

An activity represents a single screen with a user interface. For example,an email application might have one activity that shows a list of new emails,another activity to compose an email,and another activity for reading emails. Although the activities work together to form a cohesive user experience in the email application,each one is independent of the others. As such,a different application can start any one of these activities (if the email application allows it). For example,a camera application can start the activity in the email application that composes new mail,in order for the user to share a picture.

请注意我以粗体突出显示的文本部分.关键是活动本身并不是完整的应用程序,如果允许,任何第三方应用程序都可以在您的某个应用程序中调用活动.因此,通常尽可能使活动成为自包含的.一个特殊的例子是使用类似AsyncTask的东西,它提供了执行后台线程以及操作UI的方法 – 嵌套一个扩展AsyncTask的私有类是非常常见的并简化了代码.由于同样的原因,扩展BroadcastReceiver的嵌套类也很常见.

也就是说,为POJO帮助程序类使用单独的Java类文件没有任何问题,例如,它只取决于您的应用程序的复杂程度,但它可能意味着要特别考虑某些Android类的工作方式 – AsyncTask类是一个特别是如果在单独的类文件中定义,尝试它,你会明白我的意思. 原文链接：https://www.f2er.com/android/129403.html