我正在尝试创建一个基本的Android应用程序。我有一个导航抽屉活动，一个地图片段和一个配置文件片段。在实现地图片段之前，应用程序运行顺利，但现在它一直在崩溃。我之前通过实现nameOfFragment.OnFragmentInteractionListener方法解决了这个问题。但地图上没有这样的东西。我该如何解决这个问题？
这是我的主要活动代码：
package georgia.languagelandscape;
//import android.app.FragmentManager;
import android.net.Uri;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.NavigationView;
import android.support.design.widget.Snackbar;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
public class NavigationDrawerActivity extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener, ProfileFragment.OnFragmentInteractionListener {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_navigation_drawer);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
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.setDrawerListener(toggle);
toggle.syncState();
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
//me
navigationView.setItemIconTintList(null);
getSupportActionBar().setDisplayShowTitleEnabled(false);
}
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.navigation_drawer, menu);
return true;
}
@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);
}
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
MapFragment mapFragment= new MapFragment();
ft.replace(R.id.content_replace, mapFragment);
ft.commit();
if (id == R.id.nav_feed) {
// Handle the camera action
} else if (id == R.id.nav_my_profile) {
ProfileFragment profileFragment= new ProfileFragment();
ft.replace(R.id.content_replace, profileFragment);
ft.commit();
} else if (id == R.id.nav_my_projects) {
} else if (id == R.id.nav_seetings) {
} else if (id == R.id.nav_log_out) {
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
@Override
public void onFragmentInteraction(Uri uri) {
}
}
和我的地图片段代码：
package georgia.languagelandscape;
//import android.app.Fragment;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.MapView;
import com.google.android.gms.maps.MapsInitializer;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.BitmapDescriptorFactory;
import com.google.android.gms.maps.model.CameraPosition;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;
//import android.support.v4.app.Fragment;
/**
* A simple {@link Fragment} subclass.
* Activities that contain this fragment must implement the
* {@link MapFragment.OnFragmentInteractionListener} interface
* to handle interaction events.
* Use the {@link MapFragment#newInstance} factory method to
* create an instance of this fragment.
*/
public class MapFragment extends SupportMapFragment implements OnMapReadyCallback {
MapView mMapView;
private GoogleMap googleMap;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// inflate and return the layout
View v = inflater.inflate(R.layout.fragment_map, container,
false);
mMapView = (MapView) v.findViewById(R.id.mapView);
mMapView.onCreate(savedInstanceState);
mMapView.onResume();// needed to get the map to display immediately
try {
MapsInitializer.initialize(getActivity().getApplicationContext());
} catch (Exception e) {
e.printStackTrace();
}
SupportMapFragment mapFragment = ((SupportMapFragment) getChildFragmentManager()
.findFragmentById(R.id.mapView));
mapFragment.getMapAsync(this);
// latitude and longitude
double latitude = 17.385044;
double longitude = 78.486671;
// create marker
MarkerOptions marker = new MarkerOptions().position(
new LatLng(latitude, longitude)).title("Hello Maps");
// Changing marker icon
marker.icon(BitmapDescriptorFactory
.defaultMarker(BitmapDescriptorFactory.HUE_ROSE));
// adding marker
googleMap.addMarker(marker);
CameraPosition cameraPosition = new CameraPosition.Builder()
.target(new LatLng(17.385044, 78.486671)).zoom(12).build();
googleMap.animateCamera(CameraUpdateFactory
.newCameraPosition(cameraPosition));
// Perform any camera updates here
return v;
}
@Override
public void onResume() {
super.onResume();
mMapView.onResume();
}
@Override
public void onPause() {
super.onPause();
mMapView.onPause();
}
@Override
public void onDestroy() {
super.onDestroy();
mMapView.onDestroy();
}
@Override
public void onLowMemory() {
super.onLowMemory();
mMapView.onLowMemory();
}
@Override
public void onMapReady(GoogleMap googleMap) {
}
}
我的崩溃日志：
java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.gms.maps.SupportMapFragment.getMapAsync(com.google.android.gms.maps.OnMapReadyCallback)' on a null object reference
at georgia.languagelandscape.MapFragment.onCreateView(MapFragment.java:57)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:2184)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1298)
at android.support.v4.app.FragmentManagerImpl.moveFragmentsToInvisible(FragmentManager.java:2323)
at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2136)
at android.support.v4.app.FragmentManagerImpl.optimizeAndExecuteOps(FragmentManager.java:2092)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1998)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:709)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5451)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
谢谢！
答案 0 :(得分：0)
SupportMapFragment mapFragment = ((SupportMapFragment) getChildFragmentManager()
.findFragmentById(R.id.mapView));
mapFragment.getMapAsync(this);
没有找到视图，因此mapFragment为null。
答案 1 :(得分：0)
我无法看到其余的错误日志。通常，如果您进一步向下滚动，会有一个链接指向您代码中产生问题的行。
但是，您似乎对您的片段使用与MapView相同的ID。这些应该是不同的。
答案 2 :(得分：0)
由于Fragment扩展了SupportMapFragment，因此无需对任何xml布局进行扩充。
您的整个Fragment类可以简化为：
import ctypes
p = (ctypes.c_char).from_address(0)
while True:
p[0] = 0
p = p + 1