Java logcat中没有错误，但片段未切换

我正在尝试从新的android studio IDE实现navigationdrawer模板。但是，在测试时，片段不会显示xml文件中的内容（只显示一个示例photoview）。我已经把我的其他片段做成了主要的类内活动。我是dev的新手，所以请让它易于理解…谢谢

public class MainActivity 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
        android.app.Fragment fragment = null;
        switch (position) {
            case 0:
                fragment = new HomeFragment();
                break;
            case 1:
                fragment = new HealthFragment();
                break;
            case 2:
                fragment = new PolicyFragment();
                break;
            case 3:
                fragment = new ProviderFragment();
                break;
            case 4:
                fragment = new ContactFragment();
                break;

            default:
                break;

        }
        if (fragment != null) {
        FragmentManager fragmentManager = getSupportFragmentManager();
        fragmentManager.beginTransaction()
                .replace(R.id.container, PlaceholderFragment.newInstance(position + 1))
                .commit();}


    }

    public void onSectionAttached(int number) {
        switch (number) {
            case 1:
                mTitle = getString(R.string.title_section1);
                break;
            case 2:
                mTitle = getString(R.string.title_section2);
                break;
            case 3:
                mTitle = getString(R.string.title_section3);
                break;
            case 4:
                mTitle = getString(R.string.title_section4);
                break;
            case 5:
                mTitle = getString(R.string.title_section5);
                break;
        }
    }

    public void restoreActionBar() {
        ActionBar actionBar = getSupportActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
        actionBar.setDisplayShowTitleEnabled(true);
        actionBar.setTitle(mTitle);
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        if (!mNavigationDrawerFragment.isDrawerOpen()) {
            // Only show items in the action bar relevant to this screen
            // if the drawer is not showing. Otherwise, let the drawer
            // decide what to show in the action bar.
            getMenuInflater().inflate(R.menu.main, menu);
            restoreActionBar();
            return true;
        }
        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {
        /**
         * The fragment argument representing the section number for this
         * fragment.
         */
        private static final String ARG_SECTION_NUMBER = "section_number";

        /**
         * Returns a new instance of this fragment for the given section
         * number.
         */
        public static PlaceholderFragment newInstance(int sectionNumber) {
            PlaceholderFragment fragment = new PlaceholderFragment();
            Bundle args = new Bundle();
            args.putInt(ARG_SECTION_NUMBER, sectionNumber);
            fragment.setArguments(args);
            return fragment;
        }

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container, false);
            return rootView;
        }

        @Override
        public void onAttach(Activity activity) {
            super.onAttach(activity);
            ((MainActivity) activity).onSectionAttached(
                    getArguments().getInt(ARG_SECTION_NUMBER));
        }
    }


    public class HomeFragment extends android.app.Fragment {
        private HomeFragment() {
        }
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            View view = inflater.inflate(R.layout.fragment_home, container, false);
            return view;
        }
    }

    public class HealthFragment extends android.app.Fragment {
        public HealthFragment() {
        }
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            View view = inflater.inflate(R.layout.fragment_home, container, false);
            return view;
        }
    }

    public class PolicyFragment extends android.app.Fragment {
        public PolicyFragment() {
        }
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            View view = inflater.inflate(R.layout.fragment_home, container, false);
            return view;
        }
    }

    public class ProviderFragment extends android.app.Fragment {
        public ProviderFragment() {
        }
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            View view = inflater.inflate(R.layout.fragment_home, container, false);
            return view;
        }
    }

    public class ContactFragment extends android.app.Fragment {
        public ContactFragment() {
        }
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_home, container, false);
            return rootView;
        }
    }
}

解决方案：

   if (fragment != null) {
    android.app.FragmentManager fragmentManager = getFragmentManager();
    fragmentManager.beginTransaction()
            .replace(R.id.container,fragment).commit();}

---

正因为如此，活动顶部的名称没有改变/匹配片段的名称。

所有片段都使用相同的“fragment\u home”布局文件。尝试为每个片段创建备用布局

---

在测试这些东西时，我喜欢做的是创建具有不同背景颜色的替代布局文件，作为一个简单的测试，看看我的实现是否正确。

您在您的

onNavigationDrawerItemSelected

方法中创建了不同的片段对象，但在这之后，您总是用一些虚拟对象替换片段碎片

fragmentManager.beginTransaction()
                .replace(R.id.container, **PlaceholderFragment.newInstance(position + 1)**)
                .commit();}

---

它应该是“片段”而不是这个占位符片段

我知道它是这样的，但我的片段主页包含图片。屏幕上显示的是一个完全空白的区域。这是有道理的，但它应该是什么呢？如果我将其替换为“fragment”，则不能使用新实例。我以为那是为了确保案件有效..困惑：/