android.app.Fragment#isAdded ( )源码实例Demo

public void replaceFragmentByTag(Fragment fragment) {
    if (mCurrentFragment == null) {
        manager.beginTransaction().add(R.id.main_activity_container, fragment,
            fragment.getClass().getSimpleName()).commit();
    } else {
        if (fragment.isAdded()) {
            manager.beginTransaction().hide(mCurrentFragment).show(fragment).commit();
        } else {
            manager.beginTransaction().hide(mCurrentFragment)
                .add(R.id.main_activity_container, fragment,
                    fragment.getClass().getSimpleName())
                .commit();
        }
    }
    mCurrentFragment = fragment;
}
 

public void switchContent(Fragment from, Fragment to) {
    if (mContent != to) {
        mContent = to;
        FragmentTransaction transaction = getFragmentManager().beginTransaction();
        //.setCustomAnimations(android.R.anim.fade_in, android.R.anim.slide_out_right);
        if (!to.isAdded()) {    // 先判断是否被add过
            transaction.hide(from).add(R.id.content, to).commit(); // 隐藏当前的fragment，add下一个到Activity中
        } else {
            transaction.hide(from).show(to).commit(); // 隐藏当前的fragment，显示下一个
        }
    }
}
 

public static void removeDialogFragment(final String tag,
                                        final FragmentManager fragmentManager) {
  if (fragmentManager == null) {
    return;
  }
  final FragmentTransaction ft = fragmentManager.beginTransaction();
  final Fragment prev = fragmentManager.findFragmentByTag(tag);
  if (prev != null && prev.isAdded()) {
    ft.remove(prev);
  }
  ft.commitAllowingStateLoss();
}
 

public static boolean isAdded(Fragment fragment) {
    // FIXME
    return fragment.isAdded() || fragment.getTag() != null || fragment.getId() != 0;
}
 

private void selectItem(int position) {
    FragmentManager fragmentManager = getFragmentManager();
    Fragment newFragment;
    String tag;
    switch (position) {
        default:
            // Lyrics
            tag = LYRICS_FRAGMENT_TAG;
            newFragment = fragmentManager.findFragmentByTag(tag);
            if (newFragment == null || !(newFragment instanceof LyricsViewFragment))
                newFragment = new LyricsViewFragment();
            ((LyricsViewFragment) newFragment).showTransitionAnim = true;
            break;
        case 1:
            // Recent Tracks
            tag = RECENT_TRACKS_FRAGMENT_TAG;
            newFragment = fragmentManager.findFragmentByTag(tag);
            if (newFragment == null || !(newFragment instanceof RecentTracksFragment))
                newFragment = new RecentTracksFragment();
            ((RecentTracksFragment) newFragment).showTransitionAnim = true;
            break;
        case 2:
            // Saved Lyrics
            tag = LOCAL_LYRICS_FRAGMENT_TAG;
            newFragment = fragmentManager.findFragmentByTag(tag);
            if (newFragment == null || !(newFragment instanceof LocalLyricsFragment))
                newFragment = new LocalLyricsFragment();
            ((LocalLyricsFragment) newFragment).showTransitionAnim = true;
            break;
        case 3:
            // Separator
            return;
        case 4:
            // Settings
            if (drawer instanceof DrawerLayout)
                ((DrawerLayout) drawer).closeDrawer(drawerView);
            drawer.postDelayed(new Runnable() {
                @Override
                public void run() {
                    Intent settingsIntent = new Intent(MainActivity.this, SettingsActivity.class);
                    startActivityForResult(settingsIntent, 77);
                }
            }, 250);
            return;
        case 5:
            // Feedback
            return;
        case 6:
            // About Dialog
            if (drawer instanceof DrawerLayout)
                ((DrawerLayout) drawer).closeDrawer(drawerView);
            drawer.postDelayed(new Runnable() {
                @Override
                public void run() {
                    Intent aboutIntent = new Intent(MainActivity.this, AboutActivity.class);
                    startActivityForResult(aboutIntent, 77);
                }
            }, 250);
            return;
    }

    final Fragment activeFragment = getDisplayedFragment(getActiveFragments());
    prepareAnimations(activeFragment);

    // Insert the fragment by replacing any existing fragment
    if (newFragment != activeFragment) {
        if (mActionMode != null)
            mActionMode.finish();
        FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction();
        fragmentTransaction.setCustomAnimations(R.animator.slide_in_start, R.animator.slide_out_start, R.animator.slide_in_start, R.animator.slide_out_start);
        fragmentTransaction.hide(activeFragment);
        if (newFragment.isAdded())
            fragmentTransaction.show(newFragment);
        else
            fragmentTransaction.add(id.main_fragment_container, newFragment, tag);
        ((CollapsingToolbarLayout) findViewById(R.id.toolbar_layout)).setCollapsedTitleTextColor(Color.WHITE);
        fragmentTransaction.commitAllowingStateLoss();
        if (activeFragment instanceof LyricsViewFragment || newFragment instanceof LyricsViewFragment) {
            final Fragment newFragmentCopy = newFragment;
            activeFragment.getView().postDelayed(() -> {
                if (activeFragment instanceof LyricsViewFragment && activeFragment.getView() != null) {
                    expandToolbar(false);
                    showRefreshFab(false);
                } else if (newFragmentCopy instanceof LyricsViewFragment && activeFragment.getView() != null) {
                    expandToolbar(true);
                    showRefreshFab(true);
                }
            }, getResources().getInteger(android.R.integer.config_longAnimTime));
        }
        MaterialSuggestionsSearchView suggestionsSearchView = findViewById(id.material_search_view);
        if (suggestionsSearchView.isSearchOpen())
            suggestionsSearchView.closeSearch();
    }
    if (drawer instanceof DrawerLayout && (newFragment == activeFragment))
        ((DrawerLayout) drawer).closeDrawer(drawerView);
}