Android 回到抽屉导航中的第一个 fragment

Question

我有一个在 NavigationDrawer 中有多个 fragment 的应用。

下面是我的代码:

@Override
    public boolean onPrepareOptionsMenu(Menu menu) {
        // if nav drawer is opened, hide the action items
        boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
        menu.findItem(R.id.action_search).setVisible(!drawerOpen);
        return super.onPrepareOptionsMenu(menu);
    }

    /**
     * Diplaying fragment view for selected nav drawer list item
     * */
    private void displayView(int position) {
        // update the main content by replacing fragments
        fragment = null;

        switch (position) {
        case 0:
            fragment = new HomeFragment();
            break;
        case 1:
            fragment = new GalleryFragment();
            break;
        case 2:
            fragment = new ContactFragment();
            break;
        default:
            break;
        }

        if (fragment != null) {
            FragmentManager fragmentManager = getFragmentManager();
            fragmentManager.beginTransaction()
                    .replace(R.id.frame_container, fragment).commit();

            // update selected item and title, then close the drawer
            mDrawerList.setItemChecked(position, true);
            mDrawerList.setSelection(position);
            setTitle(navMenuTitles[position]);
            mDrawerLayout.closeDrawer(mDrawerList);
        } else {
            // error in creating fragment
            Log.e("MainActivity", "Error in creating fragment");
        }
    }

    @Override
    public void setTitle(CharSequence title) {
        mTitle = title;
        getActionBar().setTitle(mTitle);
    }

    /**
     * When using the ActionBarDrawerToggle, you must call it during
     * onPostCreate() and onConfigurationChanged()...
     */

    @Override
    protected void onPostCreate(Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);
        // Sync the toggle state after onRestoreInstanceState has occurred.
        mDrawerToggle.syncState();
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        // Pass any configuration change to the drawer toggls
        mDrawerToggle.onConfigurationChanged(newConfig);

    }


    @Override
    public void onBackPressed() {

        if (fragment != null) {
            FragmentManager fragmentManager = getFragmentManager();
            fragmentManager.beginTransaction()
                    .add(R.id.frame_container, fragment).commit();

            int position = 0;
            fragment = new HomeFragment();

            // update selected item and title, then close the drawer
            mDrawerList.setItemChecked(position, true);
            mDrawerList.setSelection(position);
            setTitle(navMenuTitles[position]);
            mDrawerLayout.closeDrawer(mDrawerList);
        } else {
            // error in creating fragment
            Log.e("MainActivity", "Error in creating fragment");
        } 



    } 

它的基本功能是，它首先转到 HomeFragment，当我想转到另一个 fragment MediaFragment 并决定按后退按钮返回时，我想转到 HomeFragment，当我想关闭应用程序再次按下后退按钮，它现在将关闭应用程序，就像 gmail 应用程序一样。我怎样才能做到这一点？我在使用我放入 onBackPressed() 中的代码时遇到问题。每当我转到其他 fragment 时，都会显示 HomeFragment。有任何想法吗？非常感谢您的帮助。

更新:之前，当我在 MediaFragment 中并按下后退按钮时，它会自动关闭应用程序。它不应该像，但它应该转到 HomeFragment，当它在 HomeFragment 中并且我单击后退按钮时，它会关闭应用程序。

Answer 1

与其在 onBackPressed 中复制代码，不如只跟踪最后选择的位置？

int selectedPosition = 0;

private void displayView(int position) {
    ... // All your current code
    selectedPosition = position;
}

@Override
public void onBackPressed() {
    if (selectedPosition != 0) {
        displayView(0);
    } else {
        super.onBackPressed();
}