我是Android Studio和Java语言的新手，我正在尝试基于Google Maps构建应用程序。感谢详细的解决方案。
我已经尝试过onCreateView（）和getChildFragmentManager（）。但是由于我是新手，所以我可能做错了。
我认为每次都会使我的应用崩溃的主要问题是
方法调用“ getmapasync”可能会产生“ nullpointerexception”
MapsActivity.java
package com.example.silentium50;
import androidx.annotation.RequiresApi;
import androidx.core.app.ActivityCompat;
import androidx.fragment.app.FragmentActivity;
import android.Manifest;
import android.content.pm.PackageManager;
import android.location.Address;
import android.location.Geocoder;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Build;
import android.os.Bundle;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;
import java.io.IOException;
import java.util.List;
class MapsActivity extends FragmentActivity implements OnMapReadyCallback {
public GoogleMap mMap;
LocationManager locationManager;
@RequiresApi(api = Build.VERSION_CODES.M)
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_maps);
// Obtain the SupportMapFragment and get notified when the map is ready to be used.
SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
.findFragmentById(R.id.map);
mapFragment.getMapAsync(this);
locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && checkSelfPermission(Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
// TODO: Consider calling
// Activity#requestPermissions
// here to request the missing permissions, and then overriding
// public void onRequestPermissionsResult(int requestCode, String[] permissions,
// int[] grantResults)
// to handle the case where the user grants the permission. See the documentation
// for Activity#requestPermissions for more details.
return;
}
// check if the network provider is enabled
if (locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER)){
locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 1, 1, new LocationListener() {
@Override
public void onLocationChanged(Location location) {
//get the latitude
double latitude = location.getLatitude();
//get the longitude
double longitude = location.getLongitude();
//instantiate the class, LatLng
LatLng latLng = new LatLng(latitude, longitude);
//Instantiate the class, Geocoder
Geocoder geocoder = new Geocoder(getApplicationContext());
try {
List<Address> adressList = geocoder.getFromLocation(latitude, longitude, 1);
String str = adressList.get(0).getLocality()+",";
str += adressList.get(0).getCountryName();
mMap.addMarker(new MarkerOptions().position(latLng).title(str));
mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(latLng, 30.5f));
} catch (IOException e) {
e.printStackTrace();
}
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onProviderDisabled(String provider) {
}
});
}
else if (locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER)){
locationManager.requestLocationUpdates((LocationManager.GPS_PROVIDER), 1, 1, new LocationListener() {
@Override
public void onLocationChanged(Location location) {
//get the latitude
double latitude = location.getLatitude();
//get the longitude
double longitude = location.getLongitude();
//instantiate the class, LatLng
LatLng latLng = new LatLng(latitude, longitude);
//Instantiate the class, Geocoder
Geocoder geocoder = new Geocoder(getApplicationContext());
try {
List<Address> adressList = geocoder.getFromLocation(latitude, longitude, 1);
String str = adressList.get(0).getLocality()+",";
str += adressList.get(0).getCountryName();
mMap.addMarker(new MarkerOptions().position(latLng).title(str));
mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(latLng, 10f));
} catch (IOException e) {
e.printStackTrace();
}
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onProviderDisabled(String provider) {
}
});
}
}
/**
* Manipulates the map once available.
* This callback is triggered when the map is ready to be used.
* This is where we can add markers or lines, add listeners or move the camera. In this case,
* we just add a marker near Sydney, Australia.
* If Google Play services is not installed on the device, the user will be prompted to install
* it inside the SupportMapFragment. This method will only be triggered once the user has
* installed Google Play services and returned to the app.
*/
@Override
public void onMapReady(GoogleMap googleMap) {
mMap = googleMap;
// Add a marker in Sydney and move the camera
//LatLng sydney = new LatLng(-34, 151);
//mMap.addMarker(new MarkerOptions().position(sydney).title("Marker in Sydney"));
//mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(sydney, 30.5f));
}
}
activity_maps.xlm
<?xml version="1.0" encoding="utf-8"?>
<fragment xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:map="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/map"
android:name="com.google.android.gms.maps.SupportMapFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MapsActivity" />
运行后错误：
Capturing and displaying logcat messages from application. This behavior can be disabled in the "Logcat output" section of the "Debugger" settings page.
I/art: Not late-enabling -Xcheck:jni (already on)
W/art: Unexpected CPU variant for X86 using defaults: x86
W/System: ClassLoader referenced unknown path: /data/app/com.example.silentium50-1/lib/x86
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.silentium50, PID: 7103
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.silentium50/com.example.silentium50.MapsActivity}: java.lang.IllegalAccessException: java.lang.Class<com.example.silentium50.MapsActivity> is not accessible from java.lang.Class<android.app.Instrumentation>
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2548)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
Caused by: java.lang.IllegalAccessException: java.lang.Class<com.example.silentium50.MapsActivity> is not accessible from java.lang.Class<android.app.Instrumentation>
at java.lang.Class.newInstance(Native Method)
at android.app.Instrumentation.newActivity(Instrumentation.java:1078)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2538)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
AndroidManifest.xlm
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.silentium50">
<!--
The ACCESS_COARSE/FINE_LOCATION permissions are not required to use
Google Maps Android API v2, but you must specify either coarse or fine
location permissions for the 'MyLocation' functionality.
-->
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<!--
The API key for Google Maps-based APIs is defined as a string resource.
(See the file "res/values/google_maps_api.xml").
Note that the API key is linked to the encryption key used to sign the APK.
You need a different API key for each encryption key, including the release key that is used to
sign the APK for publishing.
You can define the keys for the debug and release targets in src/debug/ and src/release/.
-->
<meta-data
android:name="com.google.android.geo.API_KEY"
android:value="@string/google_maps_key" />
<activity
android:name=".MapsActivity"
android:label="@string/title_activity_maps">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
最佳答案
从堆栈跟踪中的错误消息中，我认为您可能会在代码中的某处调用new MapsActivity()。那正确吗？
如果是这样，请不要。改为build an intent并以这种方式启动MapActivity。
更新：我可能是错的。可能是您忘记了公开您的MapsActivity吗？请编辑类定义为public class MapsActivity extends FragmentActivity implements OnMapReadyCallback {