我只是想在这里为这篇文章的未来读者补充一个更正。这个细微的差别我已经不理解很长一段时间了，所以我想确保你们没有人会犯同样的错误:
如果栈上有多个activity, System.exit()不会杀死你的应用。实际发生的情况是进程被杀死，并立即重新启动，堆栈上少了一个活动。当你的应用程序被强制关闭对话框杀死时，甚至当你试图从DDMS中杀死进程时，也会发生这种情况。据我所知，这是一个完全没有记录的事实。
The short answer is, if you want to exit your application, you've got to keep track of all activities in your stack and finish() ALL of them when the user wants to exit (and no, there is no way to iterate through the Activity stack, so you have to manage all of this yourself). Even this does not actually kill the process or any dangling references you may have. It simply finishes the activities. Also, I'm not sure whether Process.killProcess(Process.myPid()) works any better; I haven't tested it.
另一方面，如果你可以将活动保留在堆栈中，还有另一个方法可以让事情变得超级简单:Activity.moveTaskToBack(true)将简单地将你的进程作为背景并显示主屏幕。
长的答案包括对这种行为背后的哲学的解释。这一理论是基于以下几个假设:
First of all, this only happens when your app is in the foreground. If it is in the background the process will terminate just fine. However, if it is in the foreground, the OS assumes that the user wants to keep doing whatever he/she was doing. (If you are trying to kill the process from DDMS, you should hit the home button first, and then kill it)
It also assumes that each activity is independent of all the other activities. This is often true, for example in the case that your app launches the Browser Activity, which is entirely separate and was not written by you. The Browser Activity may or may not be created on the same Task, depending on its manifest attributes.
It assumes that each of your activities is completely self-reliant and can be killed/restored in a moment's notice. (I rather dislike this particular assumption, since my app has many activities which rely on a large amount of cached data, too large to be efficiently serialized during onSaveInstanceState, but whaddya gonna do?) For most well-written Android apps this should be true, since you never know when your app is going to be killed off in the background.
The final factor is not so much an assumption, but rather a limitation of the OS: killing the app explicitly is the same as the app crashing, and also the same as Android killing the app to reclaim memory. This culminates in our coup de grace: since Android can't tell if the app exited or crashed or was killed in the background, it assumes the user wants to return where they left off, and so the ActivityManager restarts the process.
仔细想想，这是适合这个平台的。首先，这正是当进程在后台被杀死，用户返回到它时所发生的情况，因此它需要在它停止的地方重新启动。其次，这是当应用程序崩溃并呈现可怕的强制关闭对话框时所发生的情况。
Say I want my users to be able to take a picture and upload it. I launch the Camera Activity from my activity, and ask it to return an image. The Camera is pushed onto the top of my current Task (rather than being created in its own Task). If the Camera has an error and it crashes, should that result in the whole app crashing? From the standpoint of the user, only the Camera failed, and they should be returned to their previous activity. So it just restarts the process with all the same Activities in the stack, minus the Camera. Since your Activities should be designed so that they can be killed and restored at the drop of a hat, this shouldn't be a problem. Unfortunately, not all apps can be designed that way, so it is a problem for many of us, no matter what Romain Guy or anyone else tells you. So, we need to use workarounds.
所以，我最后的建议是:
Don't try to kill the process. Either call finish() on all activities or call moveTaskToBack(true).
If your process crashes or gets killed, and if, like me, you need the data that was in memory which is now lost, you'll need to return to the root activity. To do this, you should call startActivity() with an Intent that contains the Intent.FLAG_ACTIVITY_CLEAR_TOP flag.
If you want to kill your app from the Eclipse DDMS perspective, it had better not be in the foreground, or it will restart itself. You should press the Home button first, and then kill the process.
