将 MyFragment 显示到 MainActivity

Question

我有两个java类。一个是main activity，另一个是MyFragment。MyFragment包含一个带有地图的片段。我想向我的MainActivity显示这个.MainActivity由导航抽屉活动组成。这两个类的代码是：

`public class MainActivity extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
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 = findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
}
@Override
public void onBackPressed() {
DrawerLayout drawer = findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();

if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.nav_loc) {
} else if (id == R.id.nav_set) {
} else if (id == R.id.nav_info) {
} else if (id == R.id.nav_abt) {
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}

} `

MyFragment代码是：

public class MyFragment extends Fragment implements OnMapReadyCallback {
GoogleMap mgoogleMap;
MapView mapView;
View view;
public MyFragment(){
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);}
@Override
public View onCreateView(LayoutInflater inflater , ViewGroup container, Bundle savedInstanceState){
view = inflater.inflate(R.layout.content_main,container , false);
return view;
}
@Override
public void onViewCreated(View view,Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
mapView = view.findViewById(R.id.map);
if(mapView!=null)
mapView.onCreate(null);
mapView.onResume();
mapView.getMapAsync(this);
}
@Override
public void onMapReady(GoogleMap googleMap){
MapsInitializer.initialize(getContext());
mgoogleMap = googleMap;
googleMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);
googleMap.addMarker(new MarkerOptions().position(new LatLng(23.2599,77.4126)).title("BHOPAL"));
CameraPosition bhopal = CameraPosition.builder().target(new LatLng(23.2599,77.4126)).zoom(16).bearing(0).build();
googleMap.moveCamera(CameraUpdateFactory.newCameraPosition(bhopal));
}

}

我怎样才能组合这两个类，以便我的主要活动显示这个片段。 如何使用 MyFragment 来主活动？

Answer 1

在Activity中声明一个成员字段，例如

private MyFragment fragment;

在onCreate()中初始化它：

fragment = MyFragment();

然后附加并显示它：

getSupportFragmentManager().beginTransaction().replace(R.id.container, fragment, "your_tag").commit()

其中container是布局的 id，应替换为Fragment的内容。

编辑：在我看来，您使用了Android Studio的"导航抽屉活动"模板。正确的布局文件将是content_main.xml(如果您尚未更改该部分(。您可以在 AS 生成的ConstraintLayout中添加内容布局：

<FrameLayout
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent" />

请注意，使用静态工厂方法进行片段实例化会是更好的方法，请查看此问题以获取更多背景信息。

Answer 2

首先，您必须在main_activity.xml中添加一个容器：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"> 
<LinearLayout
android:id="@+id/fragment_container"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
>
</LinearLayout>
</RelativeLayout>

然后在您的 MainActivity.java 中添加以下内容 onCreate(或您想要的任何位置(：

FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
MyFragment myFragment = new MyFragment();
fragmentTransaction.add(R.id.fragment_container, myFragment, "HELLO");
fragmentTransaction.commit();

传递给add()的第一个参数是应在其中放置片段的ViewGroup，由资源 ID 指定，第二个参数是要添加的片段。