android - 总是返回到主 fragment onBackpressed

Question

我已经在 Activity 中实现了 Navigation Drawer。我的应用程序中有 3-4 个 fragment 。

假设有 3 个 fragment :Fragment_1、Fragment_2、Fragment_3

当我启动我的应用程序时，Fragment_1 被加载，我使用抽屉导航转到另一个 fragment 。

原来如此

fragment _1 -> fragment _2 -> fragment _3 -> fragment _1 -> fragment _3

现在，当我按下后退按钮时，它就像

fragment _3 -> fragment _1 -> fragment _3 -> fragment _2 -> fragment _1

But, I want something like if wherever i am when i press back key, i navigate back to Fragment_1 always.

我正在使用下面的代码导航到另一个 fragment :-

nav_menu_list.setOnItemClickListener(new AdapterView.OnItemClickListener() {
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();

        switch (position) {
            case 0:
                DashboardFragment dashboardFragment = new DashboardFragment();
                fragmentTransaction.replace(R.id.mainContainer, dashboardFragment, dashboardFragment.getClass().getName());
                break;

            case 1:
                ProfileFragment profileFragment = new ProfileFragment();
                fragmentTransaction.replace(R.id.mainContainer, profileFragment, profileFragment.getClass().getName());
                fragmentTransaction.addToBackStack(null);
                break;

            case 2:
                ContactUsFragment contactUsFragment = new ContactUsFragment();
                fragmentTransaction.replace(R.id.mainContainer, contactUsFragment, contactUsFragment.getClass().getName());
                fragmentTransaction.addToBackStack(null);
                break;

            case 3:
                AboutUsFragment aboutUsFragment = new AboutUsFragment();
                fragmentTransaction.replace(R.id.mainContainer, aboutUsFragment, aboutUsFragment.getClass().getName());
                fragmentTransaction.addToBackStack(null);
                break;

            default:
                break;
        }
        fragmentTransaction.commit();
        drawer.closeDrawer(GravityCompat.START);
    }
});

请帮忙...

Answer 1

@Override
    public void onBackPressed() {

        if(!(getSupportFragmentManager().findFragmentById(R.id.mainContainer) instanceof DashboardFragment))
        {
            DashboardFragment dashboardFragment = new DashboardFragment();
            fragmentTransaction.replace(R.id.mainContainer, dashboardFragment, dashboardFragment.getClass().getName());
        }else {
            super.onBackPressed();
        }
    }

使用此方法进入主要 Activity 将解决您的问题。