每当我尝试在从 firebase 检索到的地图上显示位置时，都会出现错误 [重复]
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【中文标题】每当我尝试在从 firebase 检索到的地图上显示位置时，都会出现错误 [重复]【英文标题】：I get a error whenever I try to show a location on the map retrieved from firebase [duplicate] 【发布时间】：2019-12-17 13:16:29 【问题描述】：当我撤消所有操作时，应用程序不会崩溃，我确定代码有问题。请帮帮我。
主要活动 - 用户选择他们想要跟踪的 BUS 并将字符串发送到地图活动
private
RadioGroup route;
private FirebaseAuth mAuth;
private FirebaseDatabase mDatabase = FirebaseDatabase.getInstance();
private DatabaseReference mDatabaseReference = mDatabase.getReference().child("Locations");
public String someVariable;
TextView numberbs;
Button getLocationBtn;
private Button btnSignOut;
TextView locationText;
Button stoptracking;
Button busb1;
Button busb2;
Button busb3;
Button busb4;
Button busb5;
Button busb6;
Button busb7;
Button busb8;
Button busb9;
Button busb10;
Button busb11;
Button busb12;
Button busb13;
Button busb14;
Button busb15;
Button busb16;
TextView statusi;
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
numberbs = findViewById(R.id.busnotext);
btnSignOut = findViewById(R.id.signoutbtn);
getLocationBtn = findViewById(R.id.getLocationBtn);
numberbs = findViewById(R.id.busnotext);
busb1 = findViewById(R.id.busbtn1);
busb2 = findViewById(R.id.busbtn2);
busb3 = findViewById(R.id.busbtn3);
busb4 = findViewById(R.id.busbtn4);
busb5 = findViewById(R.id.busbtn5);
busb6 = findViewById(R.id.busbtn6);
busb7 = findViewById(R.id.busbtn7);
busb8 = findViewById(R.id.bustbtn8);
busb9 = findViewById(R.id.busbtn9);
busb10 = findViewById(R.id.busbtn10);
busb11 = findViewById(R.id.busbtn11);
busb12 = findViewById(R.id.busbtn12);
busb13 = findViewById(R.id.busbtn13);
busb14 = findViewById(R.id.busbtn14);
busb15 = findViewById(R.id.bustbtn15);
busb16 = findViewById(R.id.busbtn16);
busb1.setOnClickListener(this);
busb2.setOnClickListener(this);
busb3.setOnClickListener(this);
busb4.setOnClickListener(this);
busb5.setOnClickListener(this);
busb6.setOnClickListener(this);
busb7.setOnClickListener(this);
busb8.setOnClickListener(this);
busb9.setOnClickListener(this);
busb10.setOnClickListener(this);
busb11.setOnClickListener(this);
busb12.setOnClickListener(this);
busb13.setOnClickListener(this);
busb14.setOnClickListener(this);
busb15.setOnClickListener(this);
busb16.setOnClickListener(this);
getLocationBtn.setOnClickListener(new View.OnClickListener()
@Override
public void onClick(View v)
//startService(new Intent(this, MyService.class));
Intent intent = new Intent(MainActivity.this, MapsActivity.class);
intent.putExtra("message", someVariable);
startActivity(intent);
);
/**
Intent intent = new Intent(MainActivity.this, MapsActivity.class);
intent.putExtra("Ref", someVariable);
startActivity(intent);
*/
private void toastMessage(String message)
Toast.makeText(this, message, Toast.LENGTH_SHORT).show();
@Override
public void onClick(View v)
switch (v.getId())
case R.id.busbtn1:
someVariable ="BUS1";
numberbs.setText("Selected: BUS 1");
mDatabaseReference = mDatabase.getReference().child("Locations").child("BUS1");
break;
case R.id.busbtn2:
numberbs.setText("Selected: BUS 2");
someVariable ="BUS2";
mDatabaseReference = mDatabase.getReference().child("Locations").child("BUS2");
break;
case R.id.busbtn3:
numberbs.setText("Selected: BUS 3");
someVariable ="BUS3";
mDatabaseReference = mDatabase.getReference().child("Locations").child("BUS3");
break;
case R.id.busbtn4:
numberbs.setText("Selected: BUS 4");
someVariable ="BUS4";
mDatabaseReference = mDatabase.getReference().child("Locations").child("BUS4");
break;
case R.id.busbtn5:
numberbs.setText("Selected: BUS 5");
someVariable ="BUS5";
mDatabaseReference = mDatabase.getReference().child("Locations").child("BUS5");
break;
case R.id.busbtn6:
numberbs.setText("Selected: BUS 6");
someVariable ="BUS6";
mDatabaseReference = mDatabase.getReference().child("Locations").child("BUS6");
break;
case R.id.busbtn7:
numberbs.setText("Selected: BUS 7");
someVariable ="BUS7";
mDatabaseReference = mDatabase.getReference().child("Locations").child("BUS7");
break;
case R.id.bustbtn8:
numberbs.setText("Selected: BUS 8");
someVariable ="BUS8";
mDatabaseReference = mDatabase.getReference().child("Locations").child("BUS8");
break;
case R.id.busbtn9:
numberbs.setText("Selected: BUS 9");
someVariable ="BUS9";
mDatabaseReference = mDatabase.getReference().child("Locations").child("BUS9");
break;
case R.id.busbtn10:
numberbs.setText("Selected: BUS 10");
someVariable ="BUS10";
mDatabaseReference = mDatabase.getReference().child("Locations").child("BUS10");
break;
case R.id.busbtn11:
numberbs.setText("Selected: BUS 11");
someVariable ="BUS11";
mDatabaseReference = mDatabase.getReference().child("Locations").child("BUS11");
break;
case R.id.busbtn12:
numberbs.setText("Selected: BUS 12");
someVariable ="BUS12";
mDatabaseReference = mDatabase.getReference().child("Locations").child("BUS12");
break;
case R.id.busbtn13:
numberbs.setText("Selected: BUS 13");
someVariable ="BUS13";
mDatabaseReference = mDatabase.getReference().child("Locations").child("BUS13");
break;
case R.id.busbtn14:
someVariable ="BUS14";
numberbs.setText("Selected: BUS 14");
mDatabaseReference = mDatabase.getReference().child("Locations").child("BUS14");
break;
case R.id.bustbtn15:
numberbs.setText("Selected: BUS 15");
someVariable ="BUS15";
mDatabaseReference = mDatabase.getReference().child("Locations").child("BUS15");
break;
case R.id.busbtn16:
numberbs.setText("Selected: BUS 16");
someVariable ="BUS16";
mDatabaseReference = mDatabase.getReference().child("Locations").child("BUS16");
break;
`
MAPS ACTIVITY - 从 firebase 检索位置并将其显示在地图上
private GoogleMap mMap;
private FirebaseAuth mAuth;
String value_latitude;
String value_longitue;
double longi;
double lati;
Button Refreshh;
String valie;
Button Backkk;
private FirebaseDatabase mDatabase = FirebaseDatabase.getInstance();
private DatabaseReference mDatabaseReference = mDatabase.getReference().child("Locations");
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_maps);
Intent intent = getIntent();
String message = intent.getStringExtra("message");
Refreshh = findViewById(R.id.refresh);
Backkk = findViewById(R.id.backbtn);
mDatabaseReference = mDatabase.getReference().child("Locations").child(valie);
// Obtain the SupportMapFragment and get notified when the map is ready to be used.
valie = message;
lati = Double.valueOf(value_latitude);
longi = Double.valueOf(value_longitue);
mDatabaseReference.addValueEventListener(new ValueEventListener()
@Override
public void onDataChange(DataSnapshot dataSnapshot)
for (DataSnapshot ds : dataSnapshot.getChildren())
String value_latitude = ds.child("latitude").getValue().toString();
String value_longitue = ds.child("longitude").getValue().toString();
@Override
public void onCancelled(DatabaseError databaseError)
);
SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
.findFragmentById(R.id.map);
mapFragment.getMapAsync(this);
/**
Backkk.setOnClickListener(new View.OnClickListener()
@Override
public void onClick(View view)
Intent intent = new Intent(MapsActivity.this, MainActivity.class);
startActivity(intent);
);
Refreshh.setOnClickListener(new View.OnClickListener()
@Override
public void onClick(View view)
mMap.clear();
lati = Double.valueOf(value_latitude);
longi = Double.valueOf(value_longitue);
mDatabaseReference.addValueEventListener(new ValueEventListener()
@Override
public void onDataChange(DataSnapshot dataSnapshot)
for (DataSnapshot ds : dataSnapshot.getChildren())
String value_latitude = ds.child("latitude").getValue().toString();
String value_longitue = ds.child("longitude").getValue().toString();
@Override
public void onCancelled(DatabaseError databaseError)
);
LatLng sydney = new LatLng(lati, longi);
mMap.addMarker(new MarkerOptions().position(sydney).title(valie));
mMap.moveCamera(CameraUpdateFactory.newLatLng(sydney));
);
*/
/**
* 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(lati, longi);
mMap.addMarker(new MarkerOptions().position(sydney).title(valie));
mMap.moveCamera(CameraUpdateFactory.newLatLng(sydney));
我的 LOGCAT -
19-08-10 00:34:43.912 24741-24741/com.manavchordia.aplparent E/androidRuntime: FATAL EXCEPTION: main
Process: com.manavchordia.aplparent, PID: 24741
java.lang.RuntimeException: Unable to start activity ComponentInfocom.manavchordia.aplparent/com.manavchordia.aplparent.MapsActivity: java.lang.NullPointerException: Can't pass null for argument 'pathString' in child()
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3093)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3228)
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$H.handleMessage(ActivityThread.java:1948)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6954)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:537)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Caused by: java.lang.NullPointerException: Can't pass null for argument 'pathString' in child()
at com.google.firebase.database.DatabaseReference.child(com.google.firebase:firebase-database@@18.0.1:101)
at com.manavchordia.aplparent.MapsActivity.onCreate(MapsActivity.java:48)
at android.app.Activity.performCreate(Activity.java:7155)
at android.app.Activity.performCreate(Activity.java:7146)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1288)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3068)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3228)
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$H.handleMessage(ActivityThread.java:1948)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6954)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:537)
【问题讨论】：
【参考方案1】：错误消息表明您将 null 传递给对 child() 的调用之一。可能是这个，因为您直到稍后才为valie 赋值：
mDatabaseReference = mDatabase.getReference().child("Locations").child(valie);
在像这样使用它之前先将valie分配给一个非空值。
【讨论】：
我该怎么做？【参考方案2】：您需要在 valie 变量中设置值，例如
mDatabaseReference = mDatabase.getReference().child("Locations").child(valie).setValue(in_here_which_you_want_to_Save_in_Db);
【讨论】：
这不是正确的答案，仍然会导致同样的问题，你需要为变量valie赋值，而不是使用setValue
在您声明它时或在查询中使用之前分配valie的值以上是关于每当我尝试在从 firebase 检索到的地图上显示位置时，都会出现错误 [重复]的主要内容，如果未能解决你的问题，请参考以下文章
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