如何在Android Studio导航抽屉中设置默认片段？

Question

我正在寻找一种在我的导航抽屉中找到默认片段的方法,这不是第0项.我已经看到一些解决方案基于检查savedInstanceState是否为null但我觉得我没有访问权限这在我的onNavigationDrawerItemSelected方法中.这是我的班级:

public class Main extends ActionBarActivity
    implements NavigationDrawerFragment.NavigationDrawerCallbacks {

/**
 * Fragment managing the behaviors, interactions and presentation of the navigation drawer.
 */
private NavigationDrawerFragment mNavigationDrawerFragment;

/**
 * Used to store the last screen title. For use in {@link #restoreActionBar()}.
 */
private CharSequence mTitle;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    mNavigationDrawerFragment = (NavigationDrawerFragment)
            getSupportFragmentManager().findFragmentById(R.id.navigation_drawer);
    mTitle = getTitle();

    // Set up the drawer.
    mNavigationDrawerFragment.setUp(
            R.id.navigation_drawer,
            (DrawerLayout) findViewById(R.id.drawer_layout));
}

@Override
public void onNavigationDrawerItemSelected(int position) {
    // update the Main content by replacing fragments
    Fragment fragment = null;
    switch (position) {
        case 0:
            fragment = new HomeFragment();
            break;
        case 1:
            fragment = new HomeFragment();
            break;
        case 2:
            fragment = new HomeFragment();
            break;
        default:
            fragment = new DiscoverFragment();
    }


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

    }

}

Answer 1

答案很简单.由于DrawerLayout让您自己管理片段,因此您可以使用将在普通FragmentActivity中使用的基本FragmentManager API.

我使用以下方法使其更简单,即使当前没有添加到容器中,也将替换当前片段.只需使用您希望在onCreate()方法中默认的片段调用此方法.

public void setFragment(Fragment fragment) {
    FragmentManager fragmentManager = getSupportFragmentManager();
    fragmentManager.beginTransaction()
                   .replace(R.id.container, fragment)
                   .commit();
}

请注意,在技术上更正确使用.add(fragment)了第一个电话,而不是.replace因为你没有更换任何东西,但它其实并不重要,因为在内部,它基本上只是删除任何现有的片段,并增加了使用新的一个.add()为你 HTTP: //developer.android.com/reference/android/app/FragmentTransaction.html#replace(int,android.app.Fragment,java.lang.String)