Android，mapFragment.getMapAsync错误与空对象引用一起发生

我试图在这里使用谷歌地图的片段。 我使用了SupportMapFragment，并通过R.id.map获得该片段。 最后我使用了mapFragment.GetMapAsync（这个）

但是，它总是犯错误。我不知道为什么。。。。。。 请过来帮我一下

// MainActivity.java
package com.example.fleago;

import androidx.annotation.NonNull;

import androidx.appcompat.app.AppCompatActivity;
import androidx.core.content.ContextCompat;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentActivity;
import androidx.fragment.app.FragmentTransaction;

import android.Manifest;
import android.app.Activity;
import android.content.pm.PackageManager;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Build;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;

import com.daimajia.swipe.SwipeLayout;
import com.daimajia.swipe.util.Attributes;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.MapFragment;
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 com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
import com.sothree.slidinguppanel.SlidingUpPanelLayout;

import net.daum.android.map.MapView;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

import adapter.ListViewAdapter;

import static com.example.fleago.ARActivity.REQUEST_LOCATION_PERMISSIONS_CODE;

public class MainActivity extends AppCompatActivity implements OnMapReadyCallback {
    private GoogleMap mMap;
    private static final String TAG = "MarketListView";

    private SlidingUpPanelLayout mLayout;
    private ListViewAdapter mAdapter;
    private ArrayList<Market> list;

    private Location currentLocation;
    private LocationManager locationManager;
    boolean isGPSEnabled;
    boolean isNetworkEnabled;
    boolean locationServiceAvailable;
    private static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 1; // 10 meters
    private static final long MIN_TIME_BW_UPDATES = 100;//1000 * 60 * 1; // 1 minute
    private static final int MAX_DISTANCE = Integer.MAX_VALUE;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);
    }
    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;
        LatLng SEOUL = new LatLng(37.56, 126.97);

        MarkerOptions markerOptions = new MarkerOptions();
        markerOptions.position(SEOUL);
        markerOptions.title("Seoul");
        markerOptions.snippet("Korea's Center");
        mMap.addMarker(markerOptions);

        mMap.moveCamera(CameraUpdateFactory.newLatLng(SEOUL));
        mMap.animateCamera(CameraUpdateFactory.zoomTo(10));
    }
}

我不明白为什么getMapAsync（this）在这里为空

---

有人能告诉我为什么会这样吗？

像这样设置supportfragment

<fragment android:layout_width="match_parent" android:layout_height="match_parent" android:id="@+id/map" tools:context=".MapsActivity" class="com.google.android.gms.maps.SupportMapFragment" /> 

---

我从您的问题中观察到，您可能面临活动类的命名约定

您可能已经在清单文件中声明了它。然而，您在给定代码中使用了上面的MainActivity名称。 将其更改为MapsActivity，并检查您的清单文件是否也没有显示任何错误

如果显示错误，请将名称更改为“活动类”使用的名称。

我希望这将有助于您：

2019-09-28 17:35:13.911 18564-18564/com.example.fleago E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.fleago, PID: 18564
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.fleago/com.example.fleago.MainActivity}: 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 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3114)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3257)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1948)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7050)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:965)
     Caused by: 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 com.example.fleago.MainActivity.onCreate(MainActivity.java:74)
        at android.app.Activity.performCreate(Activity.java:7327)
        at android.app.Activity.performCreate(Activity.java:7318)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3094)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3257) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1948) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:214) 
        at android.app.ActivityThread.main(ActivityThread.java:7050) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:965) 

<fragment android:layout_width="match_parent" android:layout_height="match_parent" android:id="@+id/map" tools:context=".MapsActivity" class="com.google.android.gms.maps.SupportMapFragment" />