这是我的第一篇帖子，对任何错误表示歉意
大家好，我目前正在制作我的第一个android应用，它是一个基于组的位置跟踪器（受ATAK启发）。
到目前为止，我正在尝试实现自动密钥生成器，该密钥生成器在创建后会上传到我的Firebase数据库。目前它在基本级别上起作用。
我还有一个“我的个人资料”部分，可让我查看我的帐户用户名和电子邮件。但是，当我查看个人资料并生成团队代码时，我的应用程序崩溃了。反之亦然，因此，如果我生成团队代码然后查看我的个人资料，该应用程序也会崩溃。要使该应用程序再次正常运行，我必须从我的Firebase数据库中删除团队代码，否则无法查看我的个人资料。
预先感谢您：）
它给我的错误是：
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.project.teamtrack.User.getName()' on a null object reference
CreateTeam.java
import java.util.Random;
public class CreateTeam extends AppCompatActivity implements View.OnClickListener {
private Button buttonRegister;
private Button buttonMap;
private TextView textCode;
DatabaseReference mRef;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.createteam);
textCode = (TextView) findViewById(R.id.textCode);
buttonRegister = (Button) findViewById(R.id.buttonRegister);
buttonMap = (Button) findViewById(R.id.buttonMap);
buttonMap.setOnClickListener(this);
buttonRegister.setOnClickListener(this);
mRef = FirebaseDatabase.getInstance().getReference().child("Teams");
}
public void TeamCode () {
//generates team code
Random code = new Random();
int number1 = code.nextInt(10);
int number2 = code.nextInt(10);
int number3 = code.nextInt(10);
int number4 = code.nextInt(10);
int number5 = code.nextInt(10);
int number6 = code.nextInt(10);
String myString = String.valueOf(number1);
String myString2 = String.valueOf(number2);
String myString3 = String.valueOf(number3);
String myString4 = String.valueOf(number4);
String myString5 = String.valueOf(number5);
String myString6 = String.valueOf(number6);
String finalCode = myString+myString2+myString3+myString4+myString5+myString6;
textCode.setText(finalCode);
String TeamCode = textCode.getText().toString().trim();
mRef.push().setValue(TeamCode);
Toast.makeText(CreateTeam.this, "Team has been registered", Toast.LENGTH_LONG).show();
}
@Override
public void onClick(View view){
if (view == buttonRegister){
TeamCode();
buttonRegister.setEnabled(false);
}
if (view == buttonMap){
finish();
startActivity(new Intent(this, MapsActivity.class));
}
}
}
ProfileActivity.java
public class ProfileActivity extends AppCompatActivity implements View.OnClickListener {
private static final String TAG = "ProfileActivity";
private TextView textViewUsername;
private TextView textViewEmail;
private Button buttonLogout;
private Button buttonMap;
private String userID;
private FirebaseDatabase mFirebaseDatabase;
private FirebaseAuth mAuth;
private FirebaseAuth.AuthStateListener mAuthListener;
private DatabaseReference myRef;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_profile);
textViewEmail = (TextView) findViewById(R.id.textViewEmail);
textViewUsername = (TextView) findViewById(R.id.textViewUsername);
buttonMap = (Button) findViewById(R.id.buttonMap);
buttonLogout = (Button) findViewById(R.id.buttonLogout);
buttonLogout.setOnClickListener(this);
buttonMap.setOnClickListener(this);
mAuth = FirebaseAuth.getInstance();
mFirebaseDatabase = FirebaseDatabase.getInstance();
myRef = mFirebaseDatabase.getReference();
FirebaseUser user = mAuth.getCurrentUser();
userID = user.getUid();
mAuthListener = new FirebaseAuth.AuthStateListener() {
@Override
public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
FirebaseUser user = firebaseAuth.getCurrentUser();
if (user !=null) {
} else {
}
//...
}
};
myRef.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
ShowData(dataSnapshot);
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
private void ShowData(DataSnapshot dataSnapshot){
for (DataSnapshot ds : dataSnapshot.getChildren()){
User user = new User();
user.setName(ds.child(userID).getValue(User.class).getName());
user.setEmail(ds.child(userID).getValue(User.class).getEmail());
Log.d(TAG, "ShowData: Name: " + user.getName());
Log.d(TAG, "ShowData: Email: " + user.getEmail());
//grabs users name/email and displays it
textViewEmail.setText("Email: "+user.getEmail());
textViewUsername.setText("Username: "+user.getName());
}
}
@Override
protected void onStart() {
super.onStart();
mAuth.addAuthStateListener(mAuthListener);
}
@Override
protected void onStop() {
super.onStop();
if (mAuthListener != null) {
mAuth.removeAuthStateListener(mAuthListener);
}
}
@Override
public void onClick(View view){
if (view == buttonMap){
finish();
startActivity(new Intent(this, MapsActivity.class));
}
if (view == buttonLogout){
mAuth.signOut();
finish();
startActivity(new Intent(this, LoginActivity.class));
}
}
}
User.java
public class User {
public String name;
public String email;
public User(){
}
public User(String name, String email) {
this.name = name;
this.email = email;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
}
编辑：
要解决此问题，我必须使用listviews编写ProfileActivity
public class Profile extends AppCompatActivity implements View.OnClickListener {
private static final String TAG = "ProfileActivity";
private Button buttonLogout;
private Button buttonMap;
List<String> userlist;
ArrayAdapter<String> adapter;
ListView UserList;
private FirebaseDatabase mFirebaseDatabase;
private FirebaseAuth mAuth;
private FirebaseAuth.AuthStateListener mAuthListener;
private DatabaseReference myRef;
private String userID;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_profile);
UserList = (ListView)findViewById(R.id.UserList);
userlist = new ArrayList<>();
buttonMap = (Button) findViewById(R.id.buttonMap);
buttonLogout = (Button) findViewById(R.id.buttonLogout);
buttonLogout.setOnClickListener(this);
buttonMap.setOnClickListener(this);
mAuth = FirebaseAuth.getInstance();
myRef = FirebaseDatabase.getInstance().getReference("User");
FirebaseUser user = mAuth.getCurrentUser();
userID = user.getUid();
mAuthListener = new FirebaseAuth.AuthStateListener() {
@Override
public void onAuthStateChanged(@Nullable FirebaseAuth firebaseAuth) {
FirebaseUser user = firebaseAuth.getCurrentUser();
if (user !=null) {
} else {
}
//...
}
};
myRef.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@Nullable DataSnapshot dataSnapshot)
{
userlist.clear();
String name = dataSnapshot.child(userID).child("name").getValue().toString();
String email = dataSnapshot.child(userID).child("email").getValue().toString();
userlist.add("Name: "+name);
userlist.add("Email: "+email);
adapter = new ArrayAdapter<>(Profile.this, android.R.layout.simple_list_item_1,userlist);
UserList.setAdapter(adapter);
}
@Override
public void onCancelled(@Nullable DatabaseError databaseError) {
}
});
}
@Override
protected void onStart() {
super.onStart();
if (mAuth.getCurrentUser()== null) {
finish();
startActivity(new Intent(this, LoginActivity.class));
}
}
@Override
protected void onStop() {
super.onStop();
if (mAuthListener != null) {
mAuth.removeAuthStateListener(mAuthListener);
}
}
@Override
public void onClick(View view){
if (view == buttonMap){
finish();
startActivity(new Intent(this, MapsActivity.class));
}
if (view == buttonLogout){
mAuth.signOut();
finish();
startActivity(new Intent(this, LoginActivity.class));
}
}
}