solution:
在AndroidManifest.xml中对应的Activity中找到“android:excludeFromRecents”，把值改为false，或直接去掉该项。
android:excludeFromRecents Whether or not the task initiated by this activity should be excluded from the list of recently used applications ("recent apps"). That is, when this activity is the root activity of a new task, this attribute determines whether the task should not appear in the list of recent apps. "
true" if the task should be
excluded from the list; "
false" if it should be
included. The default value is "
false".
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相反，如果要不出现在近期任务里面，可以增加android:excludeFromRecents="true"，但貌似要apk中所有activity都加上才有用。
