尝试在空对象引用上调用虚拟方法“.MutableLiveData .getLiveData(java.lang.String)”[重复]

Question

我正在尝试实现 ViewModel 模块，但它给了我这个空指针异常错误。

这是错误：

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.ssnwa.cargoin.cargoincustomer, PID: 11374
java.lang.NullPointerException: Attempt to invoke virtual method 'androidx.lifecycle.MutableLiveData androidx.lifecycle.SavedStateHandle.getLiveData(java.lang.String)' on a null object reference
    at com.ssnwa.cargoin.cargoincustomer.DriverToPickupViewModel.getPickupLocation(DriverToPickupViewModel.java:43)
    at com.ssnwa.cargoin.cargoincustomer.DrivertoPickupActivity.onMapReady(DrivertoPickupActivity.java:287)
    at com.google.android.gms.maps.zzak.zza(Unknown Source:2)
    at com.google.android.gms.maps.internal.zzaq.dispatchTransaction(Unknown Source:12)
    at com.google.android.gms.internal.maps.zzb.onTransact(Unknown Source:12)
    at android.os.Binder.transact(Binder.java:627)
    at cj.b(:com.google.android.gms.dynamite_mapsdynamite@19831052@19.8.31 (040700-0):14)
    at com.google.android.gms.maps.internal.bb.a(:com.google.android.gms.dynamite_mapsdynamite@19831052@19.8.31 (040700-0):4)
    at com.google.maps.api.android.lib6.impl.bi.run(:com.google.android.gms.dynamite_mapsdynamite@19831052@19.8.31 (040700-0):2)
    at android.os.Handler.handleCallback(Handler.java:790)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:164)
    at android.app.ActivityThread.main(ActivityThread.java:6494)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)

这里是调用活动：

public class DrivertoPickupActivity extends AppCompatActivity implements
    OnMapReadyCallback, GoogleApiClient.ConnectionCallbacks,GoogleApiClient.OnConnectionFailedListener , RoutingListener {

public static String driverphno;
public Marker drivermarker;
public static Location driverloc=new Location("");
public static Location pickuploc=new Location("");
private DriverToPickupViewModel vm;

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

    vm = new ViewModelProvider(this).get(DriverToPickupViewModel.class);

    mpleasewait=new ProgressDialog(this);
    mpleasewait.setTitle("Please Wait ...");


    pickuploc.setLatitude(pickcordinates.latitude);
    pickuploc.setLongitude(pickcordinates.longitude);





    database=FirebaseDatabase.getInstance();
    d2=FirebaseDatabase.getInstance();
    ref=database.getReference();
    ref2=d2.getReference();

    drivername=findViewById(R.id.driver_name);
    number=findViewById(R.id.phone_number);
    kmtoreach=findViewById(R.id.reach_km_to_pickup);
    timetoreach=findViewById(R.id.reach_time_to_pickup);
    cancelbooking=findViewById(R.id.cancel_booking);
    inforide=findViewById(R.id.info_ride);




    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
            .findFragmentById(R.id.drivermap);
    mapFragment.getMapAsync(this);



    setupActions();

}

@Override
public void onMapReady(GoogleMap googleMap) {

    mMap = googleMap;
    mMap.getUiSettings().setZoomControlsEnabled(true);


    if(vm!=null){
//CRASHES AT THIS LINE AND ALL OTHER SIMILAR LINES THAT FOLLOW
        vm.getdrivername().observe(this, new Observer<String>() {
            @Override
            public void onChanged(String s) {
                drivername.setText(s);
            }
        });

        vm.getdriverphone().observe(this, new Observer<String>() {
            @Override
            public void onChanged(String s) {
                number.setText(s);
            }
        });

        vm.getdistance().observe(this, new Observer<String>() {
            @Override
            public void onChanged(String s) {
                kmtoreach.setText(s);
            }
        });

        vm.gettime().observe(this, new Observer<String>() {
            @Override
            public void onChanged(String s) {
                timetoreach.setText(s);
            }
        });
    }

}

它在这条线和所有其他类似的线都崩溃了

vm.getdrivername()

这里是 ViewModel 类

public class DriverToPickupViewModel extends ViewModel {
private SavedStateHandle mState;

public DriverToPickupViewModel(){}

public DriverToPickupViewModel(SavedStateHandle savedStateHandle){
    mState = savedStateHandle;
}

void setPickupLocation(Location L){
    mState.set("Pickup",L);
}

void setDriverLocation(Location L){
    mState.set("Driver",L);
}

void setdrivername(String drivername){
    mState.set("drivername",drivername);
}

void setdriverphone(String phone){
    mState.set("phone", phone);
}

void setdistance(String distance){
    mState.set("distance",distance);
}

void settime(String time){
    mState.set("time",time);
}

LiveData<Location> getPickupLocation(){
    return mState.getLiveData("Pickup");
}

LiveData<Location> getDriverLocation(){
    return mState.getLiveData("Driver");
}

LiveData<String> getdrivername(){
    return mState.getLiveData("drivername");
}

LiveData<String> getdriverphone(){
    return mState.getLiveData("phone");
}

LiveData<String> getdistance(){
    return mState.getLiveData("distance");
}

LiveData<String> gettime(){
    return mState.getLiveData("time");
}

}

我无法理解为什么会这样。 我检查了vm==null。这里没有崩溃，这意味着 viewmodel 不为空，但在每个 vm.get**** 方法处都会崩溃

根据最近的回答，mState 为 null，这对我来说是愚蠢的，看不到它。

但我尝试将其更正为：

        vm = new ViewModelProvider(this, new SavedStateViewModelFactory(getApplication(),this)).get(DriverToPickupViewModel.class);

我得到了错误：

Activity cannot be convert to SavedStateRegistry owner

Answer 1

vm 不为空，但mState 为空。空的构造函数没有设置mState，所以它是空的。 getdrivername 然后尝试调用空引用的方法。