我现在正在尝试做的是尝试获取已经在我的firebase数据库中的位置对象，例如：Artic base并将其存储在我创建的localeobj中，但出于某种原因，当我运行程序时，它一直说localeobj是我正确地做我的听众吗？
package com.example.spy;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import java.util.ArrayList;
import java.util.Random;
import android.content.Intent;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
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;
public class GameJoin extends AppCompatActivity implements View.OnClickListener {
private FirebaseDatabase database;
private DatabaseReference myRef;
private FirebaseUser user;
private TextView location;
private TextView role;
private TextView desc;
private Button back;
private Intent extra;
private Bundle data;
private String spy;
private Location localeObj;
private String game_code;
private Random rand;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_game);
rand = new Random();
//Firebase stuff
user = FirebaseAuth.getInstance().getCurrentUser();
database = FirebaseDatabase.getInstance();
myRef = database.getReference();
//Views
role = (TextView) findViewById(R.id.label_role);
location = (TextView) findViewById(R.id.label_location);
desc = (TextView) findViewById(R.id.descriptionText);
//Buttons
back = (Button) findViewById(R.id.button3);
//Attach a listener to the button
findViewById(R.id.button3).setOnClickListener(this);
//Retrieve data from previous activity
extra = getIntent();
data = extra.getBundleExtra("game_data");
game_code = data.getString("game_code");
//TODO: Pull location object from Firebase
myRef.child("lobby").child(game_code).child("location").addValueEventListener( new ValueEventListener() {
@Override
public void onCancelled(DatabaseError error) {
System.out.println("************************IN CANCELLED*************************************");
}
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
System.out.println("************************OUTSIDE IF*************************************");
for (DataSnapshot data : dataSnapshot.getChildren()) {
localeObj = dataSnapshot.getValue(Location.class);
System.out.println("************************IN IF*************************************");
}
}
});
myRef.child("lobby").child(game_code).child("spy").addValueEventListener( new ValueEventListener() {
@Override
public void onCancelled(DatabaseError error) {
}
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot data : dataSnapshot.getChildren()) {
spy = (String) dataSnapshot.getValue(String.class);
}
}
});
//Display a special UI if the user is a spy
if (user.getEmail().equals(spy)) {
role.setText("You are the spy. Don't get caught!");
location.setText("Mystery Location");
desc.setText("Welcome to Spy Fall. Keep your identity hidden for the length of the game, or figure out what the location is to win the game.");
} else {
role.setText(localeObj.getRole(rand.nextInt(3)));
location.setText(localeObj.getLocationName());
desc.setText("Welcome to Spy Fall. Infer who is the spy before time runs out in order to win the game.");
}
}
@Override
public void onClick(View v) {
//Stuff happens when buttons are clicked
int id = v.getId();
if (id == R.id.button3) {
//Clean up old game lobby information
myRef = database.getReference("lobby");
myRef.child(game_code).child("players").child(user.getUid()).removeValue(); //Remove all data associated with the current game
//Return to the main lobby
Intent main_lobby = new Intent(GameJoin.this, MainActivity.class);
startActivity(main_lobby);
}
}
}
这是我得到的tomcat消息
--------- beginning of crash
05-09 11:01:42.718 3083-3083/com.example.spy E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.spy, PID: 3083
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.spy/com.example.spy.GameJoin}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.example.spy.Location.getRole(java.lang.Integer)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.example.spy.Location.getRole(java.lang.Integer)' on a null object reference
at com.example.spy.GameJoin.onCreate(GameJoin.java:112)
at android.app.Activity.performCreate(Activity.java:6679)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
https://gyazo.com/2b0c1ee92f365f06b1737c99793c96b3 香港专业教育学院发布了我的数据库结构的样子
答案 0 :(得分：1)
如果您想获得locationName，请使用以下代码：
myRef.child("lobby").child(game_code).child("location").addValueEventListener( new ValueEventListener() {
@Override
public void onCancelled(DatabaseError error) {
System.out.println("************************IN CANCELLED*************************************");
}
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
System.out.println("************************OUTSIDE IF*************************************");
String locationName = (String) dataSnapshot.child("locationName").getValue();
}
})
希望它有所帮助。