java - 双击退出应用程序

Question

我有登录活动和三个片段，即加载程序，主页，参加考勤。现在，当我在主页时，我希望我的应用程序通过点击后按退出。我已经成功实现了我的目标，但双重后按也适用于参加出勤片段这是我不想要的。在点击后按的出席片段中，它应该只是转到上一个片段，但它没有发生。

这是我的代码：-

MainActivity.java

@Override
    public void onBackPressed() {

        //for(int i=0;i<getFragmentManager().getBackStackEntryCount();i++)
        Home_Screen home_screen = (Home_Screen) getFragmentManager().findFragmentByTag
                ("Home_Screen_Teacher");

        if (home_screen != null && home_screen.isVisible()) {

             DrawerLayout navigation_drawer = home_screen.getView().findViewById(R.id.drawer_layout);
            if (navigation_drawer.isDrawerOpen(GravityCompat.START)) {
                navigation_drawer.closeDrawer(Gravity.LEFT);
            }


            else {
                if (backpressedTime + 2000 > System.currentTimeMillis()) {

                    this.finish();
                    System.exit(0);
                    return;
                }
                else {
                    second=(int)(backpressedTime/1000);
                    Snackbar.make(findViewById(R.id.home_screen_teacher),"Detach",Snackbar.LENGTH_LONG).show();
                }
                backpressedTime = System.currentTimeMillis();
                    //super.onBackPressed();
                }

            }
            else{

                super.onBackPressed();
            }


        }

加载器片段.java

@Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View loadder_fragment=inflater.inflate(R.layout.fragment_loader_fragment, container, false);

        Loader=(AVLoadingIndicatorView)loadder_fragment.findViewById(R.id.loder_login);
        handler=new Handler();
        runnable=new Runnable() {
            @Override
            public void run() {
                Loader.setVisibility(View.INVISIBLE);
                timer.cancel();

                fragmentManager=getFragmentManager();
                fragmentTransaction=fragmentManager.beginTransaction();
                fragmentTransaction.setCustomAnimations(R.animator.slide_in_left,R.animator
                        .slide_out_left,R.animator.slide_in_right,R.animator.slide_out_right);
                Home_Screen home_screen=new Home_Screen();
                fragmentTransaction.replace(R.id.Home_screen_fragment_3,home_screen,
                        "Home_Screen_Teacher");
                fragmentTransaction.addToBackStack(null);
                fragmentTransaction.commit();

            }


        };

        timer=new Timer();
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                handler.post(runnable);
            }
        }, 5000,5000);



        return loadder_fragment;
    }

Home_Screen Fragmnent.java

 navigation_drawer=(DrawerLayout)Home_screen.findViewById(R.id.drawer_layout);
        navigationView=(NavigationView)Home_screen.findViewById(R.id.Navigation_view_for_teacher);
        home_screen_take_attendance_button=(Button)Home_screen.findViewById(R.id
                .home_screen_take_attendance_button);
        home_screen_take_attendance_button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                getActivity().getFragmentManager().beginTransaction().replace(R.id
                        .fragment_take_attendance,new Take_attendance(),"take_attendence")
                        .addToBackStack(null).commit();

            }
        });

Take_attendance 片段.java

 toolbar.setNavigationOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                fragmentManager=getFragmentManager();
                fragmentTransaction=fragmentManager.beginTransaction();

                fragmentTransaction.setCustomAnimations(R.animator.slide_in_left,R.animator          .slide_out_left,R.animator.slide_in_right,R.animator.slide_out_right);
                Home_Screen home_screen=new Home_Screen();      fragmentTransaction.replace(R.id.Home_screen_fragment1,home_screen,"Home_Screen_Teacher");
                fragmentTransaction.addToBackStack(null);
                fragmentTransaction.commit();
            }
        });
           //Some code

请帮忙。过去两天我一直陷入这个问题。我已经实现了我的目标，但是退出应用程序的双重压力也在我不想要的考勤片段中工作。

标签： javaandroidandroid-fragments

Answer 1

onBackPressed()在应用您的逻辑之前，检查您的后台堆栈上是否有任何片段。

例子：

@Override
public void onBackPressed() {

    int backStackCount = getSupportFragmentManager().getBackStackEntryCount();

    if (backStackCount > 0) {
        // returns to previous fragment
        getSupportFragmentManager().popBackStack();

    } else {
        // apply your "double press" logic
        super.onBackPressed();
    }
}