如何在多個片段中處理onBackPressed（）

Question

我是Android初學者，正在開發一個應用程序，其中通過一個活動使用了多個片段。

private void displaySelectedScreen(int itemId) {
        Fragment fragment = null;
        switch (itemId) {

            case R.id.nav_home:
                fragment = new HomeFragment();
                break;

            case R.id.nav_attendance:
                fragment = new AttendanceFragment();
                break;

            case R.id.nav_notification:
                fragment = new NotificationFragment();
                break;

            case R.id.nav_event:
               fragment = new EventFragment();
                break;

            case R.id.nav_fee:
               fragment = new FeesFragment();
                break;

            case R.id.nav_news:
                fragment = new NewsFragment();
                break;

        }
        if (fragment != null) {
            FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
            ft.replace(R.id.frame_container, fragment);
            ft.addToBackStack(null);
            ft.commit();
        }

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);

    }

如果抽屜已經關閉，則使用onBackPressed()方法關閉應用程序。 現在，如果當前片段為HomeFragment且當前片段不是HomeFragment那么我想關閉一個應用程序，然后替換為HomeFragment 。 我不知道是怎么回事？

public void onBackPressed() {
    DrawerLayout drawer = (DrawerLayout)findViewById(R.id.drawer_layout);
    if (drawer.isDrawerOpen(GravityCompat.START)) {
        drawer.closeDrawer(GravityCompat.START);
    } else {
        closeApp();
    }
}

Answer 1

您可以將標簽添加到片段中。 這樣，您只需要檢查標簽名稱即可。

Fragment fragment = new Fragment();
getFragmentManager().beginTransaction()
    .replace(R.id.FrameLayoutId,fragment,"TAG_NAME")
    .addToBackStack("SOURCE_TAG_NAME").commit(); 

這是檢查片段標記的方法，將其放在活動的closeApp()方法或closeApp()方法中

function void closeApp(){
    Fragment fragment = getFragmentManager().findFragmentByTag("HomeActivity");
    if (fragment != null) {
        if(fragment.isVisible()){
            HomeActivity.this.finish(); 
        }
    }
}

Answer 2

簡單來說，只需轉到HomeFragment.java並編輯onBackPressed()方法onBackPressed()使用finish()退出應用程序。
對於其他Fragment.java ，只需使用popBackStack()函數，就可以在這里搜索： https : //developer.android.com/reference/android/app/FragmentManager.html#popBackStack（）

Answer 3

在您的MainActivity類中，重寫onBackPressed並在其中顯示對話框，如下所示：

@Override
public void onBackPressed() {
    //show dialog box here 
}

在每個Fragment使用以下代碼實現onResume()方法：

     @Override
    public void onResume() {
        super.onResume();
        getView().setFocusableInTouchMode(true);
        getView().requestFocus();
        getView().setOnKeyListener(new View.OnKeyListener() {
            @Override
            public boolean onKey(View v, int keyCode, KeyEvent event) {
                if (event.getAction() == KeyEvent.ACTION_UP && keyCode == KeyEvent.KEYCODE_BACK){
              //homefragment class name     
              Class fragmentClass = HomeFragment.class;

             try {

             Fragment  fragment = (Fragment) fragmentClass.newInstance();
             FragmentManager fragmentManager = getActivity().getSupportFragmentManager();
                        fragmentManager.beginTransaction().replace(R.id.flContent, fragment).commit();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                    return true;

                }

                return false;
            }
        });
    }

Answer 4

在NavigationActivity中使用此代碼onBackPressed（）方法。 希望能解決您的問題。

@Override
public void onBackPressed() {
    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    if (drawer.isDrawerOpen(GravityCompat.START)) {
        drawer.closeDrawer(GravityCompat.START);
    } else {
        Fragment f = getVisibleFragment();// to get which fragment now 
        if (f.getClass() != MainFragment.class) {
            Fragment fragment = null;
            try {
                fragment = (Fragment) MainFragment.class.newInstance();
            } catch (Exception e) {
                e.printStackTrace();
            }

            FragmentManager fragmentManager = getSupportFragmentManager();
            fragmentManager.beginTransaction().replace(R.id.frame, fragment).commit(); // this is your framelayout
        }else {
            super.onBackPressed();
        }

    }
}

getVisibleFragment（）函數

public Fragment getVisibleFragment() {
    FragmentManager fragmentManager = NavigationActivity.this.getSupportFragmentManager();
    List<Fragment> fragments = fragmentManager.getFragments();
    if (fragments != null) {
        for (Fragment fragment : fragments) {
            if (fragment != null && fragment.isVisible())
                return fragment;
        }
    }
    return null;
}