我想在MessageActivity.java中使用此行，以使用该用户ID来获取用户名和用户的个人资料图片，以从ChatFragment.java放入MessageActivity.java中。 这是我在所有这三个java文件中编写的代码。
该行在MessageActivity.java文件中。
reference = FirebaseDatabase.getInstance().getReference("Users").child(userID);
UserAdapter.java
package com.psb.farmersmarket.Adapter;
public class UserAdapter extends RecyclerView.Adapter<UserAdapter.ViewHolder> {
private Context context;
private List<User> users1;
public UserAdapter(Context context, List<User> users1){
this.context = context;
this.users1 = users1;
}
@NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent,int viewType) {
View view = LayoutInflater.from(context).inflate(R.layout.user_item,parent, false);
return new UserAdapter.ViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull ViewHolder holder,int position) {
final User user = users1.get(position);
holder.username.setText(user.getUserName());
holder.profile_image.setImageResource(R.drawable.round_logo);
holder.itemView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(context, MessageActivity.class);
intent.putExtra("user_id", user.getUserID());
context.startActivity(intent);
}
});
}
@Override
public int getItemCount() {
return users1.size();
}
public class ViewHolder extends RecyclerView.ViewHolder{
public TextView username;
public ImageView profile_image;
public ViewHolder(@NonNull View itemView) {
super(itemView);
username = itemView.findViewById(R.id.username2);
profile_image = itemView.findViewById(R.id.profile_image);
}
}
public void filterList(ArrayList<User> filtered_Names) {
this.users1 = filtered_Names;
notifyDataSetChanged();
}
}
ChatFragment.java
package com.psb.farmersmarket.Fragments;
public class Chats_Fragment extends Fragment {
private RecyclerView recyclerView;
private UserAdapter userAdapter;
private List<User> usersList;
FirebaseUser fuser;
DatabaseReference reference;
private List<String> user_list;
@Override
public View onCreateView(LayoutInflater inflater,ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_chats_,container,false);
recyclerView = view.findViewById(R.id.chat_recycler);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(getContext()));
fuser = FirebaseAuth.getInstance().getCurrentUser();
user_list = new ArrayList<>();
reference = FirebaseDatabase.getInstance().getReference("chats");
reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
user_list.clear();
for(DataSnapshot snapshot: dataSnapshot.getChildren()){
Chat chat = snapshot.getValue(Chat.class);
assert chat != null;
if(chat.getSender().equals(fuser.getUid())){
user_list.add(chat.getReceiver());
}
if(chat.getReceiver().equals(fuser.getUid())){
user_list.add(chat.getSender());
}
}
read_chats();
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
return view;
}
private void read_chats() {
usersList = new ArrayList<>();
reference = FirebaseDatabase.getInstance().getReference("Users");
reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
usersList.clear();
for (DataSnapshot snapshot : dataSnapshot.getChildren()){
User user = snapshot.getValue(User.class);
for (String ID : user_list){
assert user != null;
if (user.getUserID().equals(ID)){
if(usersList.size() != 0){
for (User user1 : usersList){
if(!user.getUserID().equals(user1.getUserID())){
usersList.add(user);
}
}
}
else{
usersList.add(user);
}
}
}
}
userAdapter = new UserAdapter(getContext(), usersList);
recyclerView.setAdapter(userAdapter);
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
}
MessageActivity.java
package com.psb.farmersmarket;
public class MessageActivity extends AppCompatActivity {
CircleImageView profile_image;
TextView username;
FirebaseUser firebaseUser;
DatabaseReference reference;
ImageButton btn_send;
EditText text_send;
MessageAdapter messageAdapter;
List<Chat> chats;
RecyclerView recyclerView;
Intent intent;
ValueEventListener seenListener;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_message);
Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
getSupportActionBar().setTitle("");
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
toolbar.setNavigationOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActivity(new Intent(MessageActivity.this, HomeActivity.class).setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP));
}
});
recyclerView = findViewById(R.id.recyclerview);
recyclerView.setHasFixedSize(true);
LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getApplicationContext());
linearLayoutManager.setStackFromEnd(true);
recyclerView.setLayoutManager(linearLayoutManager);
username = findViewById(R.id.username);
profile_image = findViewById(R.id.profile_image);
btn_send = findViewById(R.id.btn_send);
text_send = findViewById(R.id.text_send);
intent = getIntent();
final String userID = intent.getStringExtra("userID");
firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
btn_send.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
String msg = text_send.getText().toString();
if(!msg.equals("")){
sendMessage(firebaseUser.getUid(), userID, msg);
} else {
Toast.makeText(MessageActivity.this,"You can't send empty Text Message",Toast.LENGTH_SHORT).show();
}
text_send.setText("");
}
});
assert userID != null;
reference = FirebaseDatabase.getInstance().getReference("Users").child(userID);
reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
User user = dataSnapshot.getValue(User.class);
assert user != null;
username.setText(user.getUserName());
if(user.getImageURL().equals("default")){
profile_image.setImageResource(R.mipmap.ic_launcher);
}else {
Picasso.with(getApplicationContext())
.load(user.getImageURL())
.placeholder(R.mipmap.ic_launcher)
.into(profile_image);
}
readMessage(firebaseUser.getUid(), userID, user.getImageURL());
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
seenMessage(userID);
}
private void seenMessage(final String userID){
reference = FirebaseDatabase.getInstance().getReference("Chats");
seenListener =reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
for(DataSnapshot snapshot : dataSnapshot.getChildren()){
Chat chat = snapshot.getValue(Chat.class);
assert chat != null;
if(chat.getSender().equals(firebaseUser.getUid()) && chat.getSender().equals(userID)){
HashMap <String, Object> hashMap = new HashMap<>();
hashMap.put("is seen" , true);
snapshot.getRef().updateChildren(hashMap);
}
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
private void sendMessage(String sender, String receiver, String message){
DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
HashMap<String, Object> hashMap = new HashMap<>();
hashMap.put("sender", sender);
hashMap.put("receiver", receiver);
hashMap.put("message", message);
hashMap.put("is seen", false);
reference.child("Chats").push().setValue(hashMap);
}
private void readMessage(final String myID,final String userID,final String ImageURL){
chats = new ArrayList<>();
reference = FirebaseDatabase.getInstance().getReference("Chats");
reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
chats.clear();
for(DataSnapshot snapshot : dataSnapshot.getChildren()){
Chat chat = snapshot.getValue(Chat.class);
assert chat != null;
if(chat.getReceiver().equals(myID) && chat.getSender().equals(userID) ||
chat.getReceiver().equals(userID) && chat.getSender().equals(myID)){
chats.add(chat);
}
messageAdapter = new MessageAdapter(MessageActivity.this, chats, ImageURL);
recyclerView.setAdapter(messageAdapter);
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
private void status(String status){
reference = FirebaseDatabase.getInstance().getReference("Users").child(firebaseUser.getUid());
HashMap<String, Object> hashMap = new HashMap<>();
hashMap.put("Status", status);
reference.updateChildren(hashMap);
}
@Override
protected void onResume() {
super.onResume();
status("online");
}
@Override
protected void onPause() {
super.onPause();
reference.removeEventListener(seenListener);
status("offline");
}
}
这是下面给出的数据库。
& the last is UserModel
User.java
package com.psb.farmersmarket.Model;
import com.google.firebase.database.Exclude;
import com.google.firebase.database.IgnoreExtraProperties;
import com.google.firebase.database.PropertyName;
@IgnoreExtraProperties
public class User {
private String UserName;
private String UserPhone;
private String UserDesc;
private String UserEmail;
private String UserID;
private String imageURL;
private String search;
public User(String userName,String userPhone,String userDesc,String userEmail, String userID, String imageURL, String search) {
this.UserName = userName;
this.UserPhone = userPhone;
this.UserDesc = userDesc;
this.UserEmail = userEmail;
this.UserID = userID;
this.imageURL = imageURL;
}
public User() {
}
@PropertyName("name")
public String getUserName() {
return UserName;
}
@PropertyName("name")
public void setUserName(String userName) {
UserName = userName;
}
@PropertyName("Phone No")
public String getUserPhone() {
return UserPhone;
}
@PropertyName("Phone No")
public void setUserPhone(String userPhone) {
UserPhone = userPhone;
}
@PropertyName("Description")
public String getUserDesc() {
return UserDesc;
}
@PropertyName("Description")
public void setUserDesc(String userDesc) {
UserDesc = userDesc;
}
@PropertyName("email")
public String getUserEmail() {
return UserEmail;
}
@PropertyName("email")
public void setUserEmail(String userEmail) {
UserEmail = userEmail;
}
@Exclude
public String getUserID() {
return UserID;
}
@Exclude
public void setUserID(String userID) {
UserID = userID;
}
@PropertyName("imageURL")
public String getImageURL() {
return imageURL;
}
@PropertyName("imageURL")
public void setImageURL(String imageURL) {
this.imageURL = imageURL;
}
public String getSearch() {
return search;
}
public void setSearch(String search) {
this.search = search;
}
}
＆错误在下面给出
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.psb.farmersmarket, PID: 30143
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.psb.farmersmarket/com.psb.farmersmarket.MessageActivity}: java.lang.NullPointerException: Can't pass null for argument 'pathString' in child()
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2946)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3081)
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$H.handleMessage(ActivityThread.java:1831)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:201)
at android.app.ActivityThread.main(ActivityThread.java:6806)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:873)
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@@19.3.0:96)
at com.psb.farmersmarket.MessageActivity.onCreate(MessageActivity.java:98)
at android.app.Activity.performCreate(Activity.java:7224)
at android.app.Activity.performCreate(Activity.java:7213)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1272)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2926)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3081)
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$H.handleMessage(ActivityThread.java:1831)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:201)
at android.app.ActivityThread.main(ActivityThread.java:6806)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:873)
