AppManager

public class AppManager {

    private Stack<Activity> activityStack = new Stack<>();

    //设置当前类是单例的
    private static AppManager appManager = new AppManager();
    private AppManager(){}
    public static AppManager getInstance(){
        return appManager;
    }

    public void addActivity(Activity activity){
        activityStack.add(activity);
    }

    public void removeActivity(Activity activity){
        for(int i = activityStack.size() - 1; i >= 0 ; i--) {
            if(activityStack.get(i).getClass().equals(activity.getClass())){
                activity.finish();
                activityStack.remove(i);
                break;
            }
        }
    }

    public void removeCurrent(){
//        Activity activity = activityStack.get(activityStack.size() - 1);
        Activity activity = activityStack.lastElement();
        activity.finish();
        activityStack.remove(activity);
    }

    public void removeAll(){
        for(int i = activityStack.size() - 1; i >= 0 ; i--) {
            activityStack.get(i).finish();
            activityStack.remove(i);
        }
    }

    public int size(){
        return activityStack.size();
    }
}

protected void onCreate(Bundle savedInstanceState) {
    //将当前的Activity添加到栈管理中
    AppManager.getInstance().addActivity(this);
}