Android 连续按两次back键退出系统

1.新建一个ActivityCollector类用于存放并操作Acitivity实例。

public class ActivityCollector {
    public static List<Activity> activities = new ArrayList<Activity>();

    // 添加
    public static void addActivity(Activity activity) {
        activities.add(activity);
    }

    // 移出
    public static void removeActivity(Activity activity) {
        activities.remove(activity);
    }

    // 关闭所有
    public static void finishAll() {
        for (Activity activity : activities) {
            activity.finish();
        }
    }

    // 获取当前开启的activity数量
    public static int getListSize() {
        return activities.size();
    }
}

2.在每个Activity中添加代码：

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_one);

        ActivityCollector.addActivity(this);
        
    }

protected void onDestroy() {
        super.onDestroy();
        ActivityCollector.removeActivity(this);
    }

3.在想要双击back键退出应用的Activity中添加代码：

     private long exitTime = 0;

    @Override
    public void onBackPressed() {
        // super.onBackPressed();
        if ((System.currentTimeMillis() - exitTime) > 2000) {
            Toast.makeText(getApplicationContext(), "再按一次退出程序", Toast.LENGTH_SHORT).show();
            exitTime = System.currentTimeMillis();
        } else {
            if (ActivityCollector.getListSize() > 0) {
                ActivityCollector.finishAll();
            }
            System.exit(0);
        }
    }