有退出按钮的一个重要原因是“退出”广告。在出口，可以显示一些产生收入的广告。像所有的广告一样，它还是有点烦人，但也许比那些占用宝贵屏幕空间的广告更烦人。一些广告网络提供这种广告方式。但是，真的，你不能只是放一个退出按钮，在显示广告后什么都不做!

因此，在某些情况下需要一种或另一种方式来终止程序，而“永远不应该被需要”可能不是最全面的答案。

可能会使用Activity.finish()或System.exit(0)。

如果你指定API >= 16, Activity#finishAffinity()可以满足你的需求。

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。

博客文章“何时在Android应用程序中包含退出按钮”(提示:永远不要)解释得比我好得多。我希望每个Android开发者都读过这本书。

摘录:

In my experience what [the users] really want is: An unambiguous way to guarantee that an app will stop consuming resources (battery, CPU cycles, data transfer, etc.). Many users perceive that an exit button implements this requirement and ask for it to be added. Developers, looking to please their users, obligingly add one. Shortly thereafter they both fail. In most cases the exit button simply calls Activity.finish(). This is exactly equivalent to hitting the back button. Exactly. Services keep running and polling keeps happening. Users may think they've killed the app but they haven't, and soon they'll be even more annoyed. Exit behavior is now ambiguous. Should your exit button just close the Activity, or should it also stop all associated Services, Receivers, and Alarms? What should Back do? What happens if they hit Home instead? What happens if your app has a widget? Should the exit button stop that from updating too? The solution is to make the back button behave as you'd expect the exit button to. Better yet, simply stop consuming resources whenever the app isn't visible.

继续阅读完整的文章。

All of my applications have quit buttons... and I quite frequently get positive comments from users because of it. I don't care if the platform was designed in a fashion that applications shouldn't need them. Saying "don't put them there" is kind of ridiculous. If the user wants to quit... I provide them the access to do exactly that. I don't think it reduces how Android operates at all and seems like a good practice. I understand the life cycle... and my observation has been that Android doesn't do a good job at handling it.... and that is a basic fact.

如果你有10个，20个…有多个活动正在运行，你想要完成所有活动并退出系统。

在应用程序类或常量类中创建静态数组。

常量

public class Constants {

public static ArrayList<Activity> activities = new ArrayList<Activity>();

}

在此数组中添加当前活动引用

activity = MainActivity.this; Constants.activities.add(活动);

public class MainActivity extends Activity {

    private ImageView imageButton;
    private Activity activity;


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        activity = MainActivity.this;
        Constants.activities.add(activity);

        imageButton = (ImageView) findViewById(R.id.camera);
        imageButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                // existing app.
                if (Constants.activities != null) {
                    for (int i = 0; i < Constants.activities.size(); i++) {
                        Activity s = Constants.activities.get(i);
                        s.finish();
                    }
                }
                //super.finish();
                finish();
                android.os.Process.killProcess(android.os.Process.myPid());
                System.exit(1);
            }
        });
    }
}