如何在app load上实现默认活动（片段）。 （抽屉布局）

Question

我正在使用片段并成功设置了所有活动。一切都功能齐全。

我的问题是，当应用程序最初启动时，我似乎无法加载默认布局或片段类。

我尝试了一些奇怪的结果。这是我MainActivity的代码。

public class MainActivity extends AppCompatActivity
  implements NavigationView.OnNavigationItemSelectedListener {

  @Override
  protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
            this, drawer, toolbar, R.string.navigation_drawer_open, 
    R.string.navigation_drawer_close);
    drawer.addDrawerListener(toggle);
    toggle.syncState();

    NavigationView navigationView = (NavigationView) 
    findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(this);

}

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

@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
    int id = item.getItemId();
    Fragment fragment = null;


    if (id == home) {
        fragment = new Home();
    } else if (id == services) {
        fragment = new Services();
    } else if (id == beforeAfter) {
        fragment = new BeforeAfter();
    } else if (id == staff) {
        fragment = new Staff();
    } else if (id == patientInfo) {
        fragment = new Patient();
    } else if (id == blog) {
        fragment = new Blog();
    } else if (id == contactUs) {
        fragment = new Contact();
    }

    if (fragment != null) {

        android.support.v4.app.FragmentManager fragmentManager = 
        getSupportFragmentManager();
        FragmentTransaction ft = fragmentManager.beginTransaction();

        ft.replace(R.id.screen_area, fragment);
        ft.commit();
    }

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

这是Home.class的片段代码

public class Home extends Fragment {
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup 
container, @Nullable Bundle savedInstanceState) {
    return inflater.inflate(R.layout.home, null);

}

}

编辑我的MainActivity java文件并附加onCreate

后

FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
    ft.replace(R.id.screen_area, new Home());
    ft.commit();

它现在有效。我想我正在分配Home片段的XML布局页面的名称，而不是content_main下的FrameLayout的ID。

Answer 1

你的代码看起来很好。我想问题出在你的activity_main.xml

中

确保DrawerLayout内只有两个孩子 一个用于主容器，另一个用于NavigationView

<android.support.v4.widget.DrawerLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <!-- The main content view -->
    <FrameLayout
        android:id="@+id/content_frame"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
    <!-- The navigation drawer -->
    <android.support.design.widget.NavigationView
         android:id="@+id/nav_view"
         android:layout_width="wrap_content"
         android:layout_height="match_parent"
         android:layout_gravity="start"
         app:menu="@menu/my_navigation_items" />
</android.support.v4.widget.DrawerLayout>

您需要在onCreate

中显示您的片段

    FragmentTransaction mFragmentTransaction = getSupportFragmentManager().beginTransaction();
    ft.replace(R.id.content_frame, new YourFragment());
    ft.commit(); //important

Answer 2

在你的onCreate中调用片段

FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
    ft.replace(R.id.content_frame, new Fragment1());
    ft.commit();