继续学习Android,我读了以下内容:

Question: Does the user have a choice to kill the application unless we put a menu option in to kill it? If no such option exists, how does the user terminate the application? Answer: (Romain Guy): The user doesn't, the system handles this automatically. That's what the activity lifecycle (especially onPause/onStop/onDestroy) is for. No matter what you do, do not put a "quit" or "exit" application button. It is useless with Android's application model. This is also contrary to how core applications work.

呵呵,我在Android世界里每走一步都会遇到一些问题=(

显然,你不能在Android中退出应用程序(但Android系统可以随时完全销毁你的应用程序)。这是怎么回事?我开始认为这是不可能写一个应用程序的功能作为“正常的应用程序”-用户可以退出应用程序时,他/她决定这么做。这不应该依靠操作系统来完成。

我正在尝试创建的应用程序不是Android市场的应用程序。它不是一个被大众“广泛使用”的应用程序,它是一个将在非常狭窄的商业领域使用的商业应用程序。

我其实很期待为Android平台开发,因为它解决了Windows Mobile和。net中存在的许多问题。然而,上周对我来说有点令人失望……我希望我不必放弃Android,但它现在看起来不太好=(

有办法让我真的退出应用程序吗?


当前回答

我会考虑阅读Addison-Wesley出版的“Android Wireless Application Development”。我刚刚完成它,它是非常彻底的。

看来你对Android平台有一些基本的误解。一开始我也对Android应用程序的生命周期感到有点沮丧,但在更深入地了解后,我开始真正享受这种方法。这本书将回答你所有的问题,甚至更多。这确实是我为Android新开发者找到的最好的资源。

Also, I think you need to let go of a line-for-line port of the existing app. In order to port your application to the Android platform, some of the application design is going to change. The application-lifecycle used is necessary as mobile devices have very limited resources relative to desktop systems and allows Android devices to run several applications in an orderly and resource-aware fashion. Do some more in depth study of the platform, and I think you will realize that what you are wanting to do is entirely feasible. Best of luck.

顺便说一下,我与艾迪生-卫斯理或与这本书有关的任何个人或组织都没有任何关系。重读了我的帖子后,我觉得我有点像个迷弟。我真的非常非常喜欢它,而且发现它非常有帮助。:)

其他回答

在Intent中使用FLAG_ACTIVITY_CLEAR_TOP标志关闭应用程序,然后system.exit();

或者有类似的方法,但是没有system.exit()当你想退出时调用这个方法:

public void exit() {
    startActivity(new Intent(this, HomeActivity.class).
    setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | IntentCompat.FLAG_ACTIVITY_CLEAR_TASK).putExtra(EXIT_FLAG, true));
}

在你的HomeActivity.onCreate()中添加以下代码

protected void onCreate(Bundle savedInstanceState) {
    if (getIntent().getBooleanExtra(EXIT_FLAG, false)) {
        if ((getIntent().getFlags() & Intent.FLAG_ACTIVITY_LAUNCHED_FROM_HISTORY) == 0) {
            finish();
        }
    }
......................

这将在不破坏Android生命周期的情况下工作。

我花了更长的时间来阅读这个问答,而不是真正实现一个半正确的Android应用程序生命周期。

这是一个GPS应用程序,轮询积分,并每隔几秒钟通过线程将当前位置发送到web服务…在Ted的情况下,这可能是每5分钟轮询一次更新,然后onStop可以简单地启动Ted所关心的更新活动,如果发现了一个(异步Ted,不要像Windows程序员那样编码,否则您的程序将像Windows程序一样运行……呃,这也没那么难)。

我在onCreate中做了一些初始代码来设置活动生命周期,包括checkUpdate.start();:

...

@Override
public void onStart() {
    super.onStart();
    isRemote = true;
    checkUpdate.resume();

    locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 2000, 0, luh);
}

@Override
public void onPause() {
    isRemote = false;
    checkUpdate.suspend();
    locationManager.removeUpdates(luh);
    super.onStop();
}

这段代码可能是完全错误的,但它是有效的。这是我的第一个Android应用程序。

Voilà, an application that doesn't consume CPU when it's in the background, yet is instantly ready to reopen because it is in RAM (although not holding RAM as is the Android lifecycle) ... an app is always ready, it's a phone, guys/gals. If an app was to use up all the RAM and couldn't be shut down by the OS then the thing might stop ringing =P That's why the OS needs to be able to close your app when it's in the background (if your application isn't a resource hog it won't be closed BTW), so let's just write better applications.

这场争论可以归结为一个古老的问题:究竟是开发人员最了解,还是用户最了解。所有人为因素领域的专业设计师每天都在与这个问题作斗争。

Ted指出,市场上下载最多的应用之一是“应用杀手”。当人们停止应用时,他们会获得额外的血清素。他们已经习惯了台式机/笔记本电脑。它能让事情快速发展。它能让处理器保持凉爽,风扇也不会打开。它耗电更少。

当你认为移动设备是一艘小得多的船时,你就会特别感激他们“抛弃你不再需要的东西”的动机。现在,Android的开发者们认为操作系统才是最清楚的,退出一个应用程序已经过时了。我全心全意地支持这一点。

然而,我也认为你不应该让用户感到沮丧,即使这种沮丧是出于他们自己的无知。因此,我认为有一个“退出”选项是很好的设计,即使它只是一个安慰剂按钮,只是关闭一个视图。

几乎99%的情况下,Android应用程序不需要接管自己的生命周期。大多数情况下,这归结于更好的计划或更聪明的应用程序设计。例如,构建一个内部服务(不导出)来处理下载等,或者围绕用户工作流设计动作和任务。

但话虽如此,有志者事竟成。Android通过Android .os. process类提供了一个比Java更好的API来控制底层进程。与Java不同的是,它不会把开发人员当成傻瓜,把所有问题都隐藏在一个简单的Java .lang. system .exit()调用之后。

那么如何让你的应用在Android中自杀呢?诀窍很简单:

通过继承标准Android .app. application类来创建自己的Android应用程序类(记得在AndroidManifest.xml文件中声明它)。

重写onCreate()方法,并存储启动应用程序的进程ID:

this.pid = android.os.Process.myPid(); // Save for later use.

现在要杀死你的应用程序,提供一个kill()方法:

android.os.Process.sendSignal(pid, android.os.Process.SIGNAL_KILL);

现在,无论何时你需要你的应用自杀,只要输入转换应用上下文,并调用你的kill方法!

((MySuicidalApp) context.getApplicationContext()).kill()

请记住,由于Android中的进程管理策略,特别是与服务相关的策略,Android可能只是选择重新启动你的服务(参见你不应该在Android上使用任务杀手)。

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.