问题
I'm studying with AOSP, and I found ActivityStack and TaskRecord in "ActivityStack" Class. There is explanation In https://developer.android.com/guide/components/tasks-and-back-stack , Back-stack(=Activity Stack) And Task seems similar to me... What is the the difference between ActivityStack and TaskRecord?
回答1:
In this https://developer.android.com/guide/components/tasks-and-back-stack,
Focus on below lines, For Task
A task is a cohesive unit that can move to the "background" when users begin a new task or go to the Home screen, via the Home button. While in the background, all the activities in the task are stopped.
For back stack
The back stack for the task remains intact—the task has simply lost focus while another task takes place. A task can then return to the "foreground" so users can pick up where they left off.
For info you can refer below links:-
What is the relationship between Task and Back stack
https://blog.mindorks.com/android-task-and-back-stack-review-5017f2c18196
https://medium.com/google-developers/tasks-and-the-back-stack-dbb7c3b0f6d4
回答2:
If you think of activity back stack as two levels, it might be easier to understand the purpose of ActivityStack. Android supports launchMode and taskAffinity to put activities into different TaskRecords. But even activities are put into different TaskRecords, it keeps supporting the back button to switch back to previous activity. So when you launch activity that needs to be in new TaskRecord, then back button is pressed, it switches to top activity of previous TaskRecord. So ActivityStack is more like a TaskRecord stack, and TaskRecord is more like the activity stack inside the TaskRecord, however, general speaking, ActivityStack controls the pop up sequence, and you can say it's an indirect activity stack.
And creating ActivityStack seems to make management easier logically in multiple window environment. If you enable free form in Android, each launched window mode app has its own free form stack, and each stack has its own back stack.
My 2c.
来源：https://stackoverflow.com/questions/50087669/what-is-the-difference-between-activitystack-and-taskrecord