英文:
Unable to display contact list in Android Studio using RecyclerView
问题
我正在尝试在我的移动应用程序中显示我的联系人列表。我已经连接了数据库，我发现数据库没有问题，因为我可以添加新联系人，但是我无法显示列表。我使用了RecyclerView，我已经创建了适配器类、项目布局和模型。
- 适配器类 - contAdapter.java
- 项目布局 - item.xml
- 模型 - Contact
- RecyclerView 布局 - contactList.xml
- contactList - 用于将 RecyclerView 与适配器绑定
我希望看到已添加到数据库的联系人列表显示在屏幕上，但我已经卡在这里很长时间，因为我无法找出问题在哪里 
这是我的联系人模型：
public Contact() {
}
public Contact(String contName, String contNumber) {
this.contName = contName;
this.contNumber = contNumber;
}
public String getContName() {
return contName;
}
public void setContName(String contName) {
this.contName = contName;
}
public String getContNumber() {
return contNumber;
}
public void setContNumber(String contNumber) {
this.contNumber = contNumber;
}
contactList.xml：
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_margin="25dp"
tools:context=".MainActivity">
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/contList"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toTopOf="parent"/>
</androidx.constraintlayout.widget.ConstraintLayout>
contactList.java：
package com.example.lucentproj;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import android.os.Bundle;
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;
import java.util.ArrayList;
public class contactList extends AppCompatActivity {
RecyclerView recyclerView;
DatabaseReference reference;
contAdapter adapter;
ArrayList<Contact> list;
FirebaseUser user;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_contact_list);
user = FirebaseAuth.getInstance().getCurrentUser();
recyclerView = findViewById(R.id.contList);
reference = FirebaseDatabase.getInstance().getReference("Contact");
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
list = new ArrayList<>();
adapter = new contAdapter(this, list);
recyclerView.setAdapter(adapter);
reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot snapshot) {
for (DataSnapshot dataSnapshot : snapshot.getChildren()) {
Contact contact = dataSnapshot.getValue(Contact.class);
list.add(contact);
}
adapter.updateList(list);
}
@Override
public void onCancelled(@NonNull DatabaseError error) {
}
});
}
}
item.xml：
<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent" android:layout_height="wrap_content"
xmlns:app="http://schemas.android.com/apk/res-auto" android:layout_margin="16dp"
app:cardElevation="8dp" app:cardCornerRadius="8dp">
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="16dp"
android:orientation="vertical"/>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_vertical"
android:orientation="horizontal" />
<TextView
android:id="@+id/contname"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:fontFamily="@font/amaranth"
android:text="Name"
android:layout_marginLeft="10dp"
android:layout_marginTop="8dp"
android:textSize="20sp"
android:textStyle="bold" />
<TextView
android:id="@+id/contno"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="30dp"
android:fontFamily="@font/amaranth_italic"
android:paddingLeft="10dp"
android:text="Number"
android:textSize="20dp"
android:textStyle="italic" />
<ImageView
android:id="@+id/cCall"
android:layout_width="38dp"
android:layout_height="30dp"
android:layout_marginLeft="280dp"
android:layout_marginTop="15dp"
android:clickable="true"
android:src="@drawable/call" />
<ImageView
android:id="@+id/cEdit"
android:layout_width="45dp"
android:layout_height="30dp"
android:layout_marginLeft="320dp"
android:layout_marginTop="15dp"
android:clickable="true"
android:src="@drawable/edit" />
</androidx.cardview.widget.CardView>
contAdapter：
package com.example.lucentproj;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import java.util.ArrayList;
public class contAdapter extends RecyclerView.Adapter<contAdapter.ViewHolder> {
Context context;
ArrayList<Contact> list;
public contAdapter(Context context, ArrayList<Contact> list) {
this.context = context;
this.list = list;
}
@NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View v = LayoutInflater.from(context).inflate(R.layout.item, parent, false);
return new ViewHolder(v);
}
@Override
public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
Contact cont = list.get(position);
holder.cname.setText(cont.getContName());
holder.cnum.setText(cont.getContNumber());
}
@Override
public int getItemCount() {
return list.size();
}
public static class ViewHolder extends RecyclerView.ViewHolder {
TextView cname
<details>
<summary>英文:</summary>
I am trying to display my contact list for my mobile application. I have already connected the database and I figured that there is no problem with the database since I can add new contact but I am unable to display the list. I use RecyclerView which I already created Adapter class, item layout and model for.
* Adapter class - contAdapter.java
* item layout - item.xml
* Model - Contact
* RecyclerView Layout - contactList.xml
* contactList - to bind recyclerview with adapter
I wish to see the list of contact added to the database to be displayed on the screen but I have been stuck here for quite some time since I cannot figure out what the problem is :(
Here is my Contact Model:
public Contact() {
}
public Contact(String contName, String contNumber) {
this.contName = contName;
this.contNumber = contNumber;
}
public String getContName() {
return contName;
}
public void setContName(String contName) {
this.contName = contName;
}
public String getContNumber() {
return contNumber;
}
public void setContNumber(String contNumber) {
this.contNumber = contNumber;
}
`contactList.xml`:
```xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_margin="25dp" tools:context=".MainActivity">
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/contList"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toTopOf="parent"/>
</androidx.constraintlayout.widget.ConstraintLayout>
contactList.java:
package com.example.lucentproj;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import android.os.Bundle;
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;`
import java.util.ArrayList;
public class contactList extends AppCompatActivity {
RecyclerView recyclerView;
DatabaseReference reference;
contAdapter adapter;
ArrayList<Contact> list;
FirebaseUser user;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_contact_list);
user = FirebaseAuth.getInstance().getCurrentUser();
recyclerView = findViewById(R.id.contList);
reference = FirebaseDatabase.getInstance().getReference("Contact");
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
list = new ArrayList<>();
adapter = new contAdapter(this, list);
recyclerView.setAdapter(adapter);
reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot snapshot) {
for (DataSnapshot dataSnapshot : snapshot.getChildren()){
Contact contact = dataSnapshot.getValue(Contact.class);
list.add(contact);
}
adapter.updateList(list);
}
@Override
public void onCancelled(@NonNull DatabaseError error) {
}
});
}
}
item.xml:
<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent" android:layout_height="wrap_content"
xmlns:app="http://schemas.android.com/apk/res-auto" android:layout_margin="16dp"
app:cardElevation="8dp" app:cardCornerRadius="8dp">
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="16dp"
android:orientation="vertical"/>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_vertical"
android:orientation="horizontal" />
<TextView
android:id="@+id/contname"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:fontFamily="@font/amaranth"
android:text="Name"
android:layout_marginLeft="10dp"
android:layout_marginTop="8dp"
android:textSize="20sp"
android:textStyle="bold" />
<TextView
android:id="@+id/contno"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="30dp"
android:fontFamily="@font/amaranth_italic"
android:paddingLeft="10dp"
android:text="Number"
android:textSize="20dp"
android:textStyle="italic" />
<ImageView
android:id="@+id/cCall"
android:layout_width="38dp"
android:layout_height="30dp"
android:layout_marginLeft="280dp"
android:layout_marginTop="15dp"
android:clickable="true"
android:src="@drawable/call" />
<ImageView
android:id="@+id/cEdit"
android:layout_width="45dp"
android:layout_height="30dp"
android:layout_marginLeft="320dp"
android:layout_marginTop="15dp"
android:clickable="true"
android:src="@drawable/edit" />
</androidx.cardview.widget.CardView>
contAdapter:
package com.example.lucentproj;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup; import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import java.util.ArrayList;
public class contAdapter extends RecyclerView.Adapter<contAdapter.ViewHolder> {Context context;
ArrayList<Contact> list;
public contAdapter(Context context, ArrayList<Contact> list) {
this.context = context;
this.list = list;
}
@NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View v = LayoutInflater.from(context).inflate(R.layout.item,parent,false);
return new ViewHolder(v);
}
@Override
public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
Contact cont = list.get(position);
holder.cname.setText(cont.getContName());
holder.cnum.setText(cont.getContNumber());
}
@Override
public int getItemCount() {
return list.size();
}
public static class ViewHolder extends RecyclerView.ViewHolder {
TextView cname, cnum;
public ViewHolder(@NonNull View itemView) {
super(itemView);
cname = itemView.findViewById(R.id.contName);
cnum = itemView.findViewById(R.id.contNumber);
}
}
public void updateList(ArrayList<Contact> list){
this.list=list;
notifyDataSetChanged();
}
}
答案1
得分: 1
你没有在适配器中更新列表
请在你的适配器类中添加这个方法 -
public void updateList(ArrayList<Contact> list){
this.list = list;
notifyDataSetChanged();
}
并且将联系列表活动中的这一行代码替换为 adapter.updateList(list);，而不是 adapter.notifyDataSetChanged();。
contactList.java
package com.example.lucentproj;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import android.os.Bundle;
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;
import java.util.ArrayList;
public class contactList extends AppCompatActivity {
RecyclerView recyclerView;
DatabaseReference reference;
contAdapter adapter;
ArrayList<Contact> list;
FirebaseUser user;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_contact_list);
user = FirebaseAuth.getInstance().getCurrentUser();
recyclerView = findViewById(R.id.contList);
reference = FirebaseDatabase.getInstance().getReference("Contact");
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
list = new ArrayList<>();
reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot snapshot) {
list.clear(); // 清空列表以防止重复添加
for (DataSnapshot dataSnapshot : snapshot.getChildren()) {
Contact contact = dataSnapshot.getValue(Contact.class);
list.add(contact);
}
adapter.updateList(list); // 更新适配器的数据
}
@Override
public void onCancelled(@NonNull DatabaseError error) {
}
});
adapter = new contAdapter(this, list);
recyclerView.setAdapter(adapter);
}
}
请确保按照上述方式更新你的代码。
英文:
You are not updating list in Adaptor
Please add this method in your adaptor class -
public void updateList(ArrayList<Contact> list){
this.list=list;
notifyDataSetChanged();
}
And replace this line from your contactList activity to adapter.notifyDataSetChanged(); --> adapter.updateList(list);
contactList.java
package com.example.lucentproj;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import android.os.Bundle;
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;`
import java.util.ArrayList;
public class contactList extends AppCompatActivity {
RecyclerView recyclerView;
DatabaseReference reference;
contAdapter adapter;
ArrayList<Contact> list;
FirebaseUser user;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_contact_list);
user = FirebaseAuth.getInstance().getCurrentUser();
recyclerView = findViewById(R.id.contList);
reference = FirebaseDatabase.getInstance().getReference("Contact");
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
list = new ArrayList<>();
myRef.addChildEventListener(new ChildEventListener() {
@Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
Contact contact = dataSnapshot.getValue(Contact.class);
list.add(contact);
}
}
adapter = new contAdapter(this, list);
recyclerView.setAdapter(adapter);
reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot snapshot) {
for (DataSnapshot dataSnapshot : snapshot.getChildren()){
Contact contact = dataSnapshot.getValue(Contact.class);
list.add(contact);
}
adapter.updateList(list);
}
@Override
public void onCancelled(@NonNull DatabaseError error) {
}
});
}
}
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