使用 fusedLocationProviderClient.requestLocationUpdates 时出现“由以下原因引起：java.lang.NullPointerException：监听器不得为空”

Question

这是该应用程序的第二个活动。我已经在第一个活动中请求访问位置的权限。这是错误：

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java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.livelocationfinder/com.example.livelocationfinder.MapsActivity}: java.lang.NullPointerException: Listener must not be null\n        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3123)\n        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3266)\n        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)\n        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)\n        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)\n        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1957)\n        at android.os.Handler.dispatchMessage(Handler.java:106)\n        at android.os.Looper.loop(Looper.java:214)\n        at android.app.ActivityThread.main(ActivityThread.java:7099)\n        at java.lang.reflect.Method.invoke(Native Method)\n        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494)\n        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:965)\n     Caused by: java.lang.NullPointerException: Listener must not be null\n        at com.google.android.gms.common.internal.Preconditions.checkNotNull(Unknown Source:11)\n        at com.google.android.gms.common.api.internal.ListenerHolders.createListenerHolder(Unknown Source:13)\n        at com.google.android.gms.location.FusedLocationProviderClient.requestLocationUpdates(Unknown Source:14)\n        at com.example.livelocationfinder.MapsActivity.onCreate(MapsActivity.java:54)\n        at android.app.Activity.performCreate(Activity.java:7327)\n        at android.app.Activity.performCreate(Activity.java:7318)\n        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1275)\n        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3103)\n        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3266)\xc2\xa0\n        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)\xc2\xa0\n        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)\xc2\xa0\n        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)\xc2\xa0\n        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1957)\xc2\xa0\n        at android.os.Handler.dispatchMessage(Handler.java:106)\xc2\xa0\n        at android.os.Looper.loop(Looper.java:214)\xc2\xa0\n        at android.app.ActivityThread.main(ActivityThread.java:7099)\xc2\xa0\n        at java.lang.reflect.Method.invoke(Native Method)\xc2\xa0\n        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494)\xc2\xa0\n        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:965)\xc2\xa0\n2020-04-01 22:44:27.324 30588-30588/com.example.livelocationfinder I/Process: Sending signal. PID: 30588 SIG: 9\n

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这是该方法的代码onCreate()，我在最后一行收到错误。\nlocationCallback已初始化onMapReady()方法中初始化。

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 protected void onCreate(Bundle savedInstanceState) {\n    super.onCreate(savedInstanceState);\n    setContentView(R.layout.activity_maps);\n    // Obtain the SupportMapFragment and get notified when the map is ready to be used.\n    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()\n            .findFragmentById(R.id.map);\n    mapFragment.getMapAsync(this);\n    fusedLocationProviderClient = LocationServices.getFusedLocationProviderClient(MapsActivity.this);\n    locationRequest = LocationRequest.create();\n    locationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);\n    locationRequest.setInterval(5000);\n    fusedLocationProviderClient.requestLocationUpdates(locationRequest,locationCallback,Looper.getMainLooper());\n

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Answer 1

locationCallback您是否在代码中的任何位置初始化？您应该在将该对象传递给“requestLocationUpdates”之前对其进行初始化。例如，像这样：

    locationCallback = new LocationCallback(){
            @Override
            public void onLocationResult(LocationResult locationResult) {
                super.onLocationResult(locationResult);

                // Do something with locationResult
            }
        };