java - RecyclerView 在对象删除时更新视图,最后一个对象除外
问题描述
在我的应用程序中,我有一个活动,它在 RecyclerView 中显示学生的 ArrayList。学生存储在 Firebase 实时数据库中。用户可以添加或删除学生。当用户删除一个学生时,RecyclerView 会更新并显示剩余的学生。
但我有一个问题。例如,假设我有 5 个学生。我想删除所有 5 个,所以我将它们一个一个删除。4 名学生正确删除,RecyclerView 更新并反映了这一点。只有当我删除最后一个学生时,RecyclerView 才不会更新并且学生 CardView 会留在那里。我收到一条确认学生删除的敬酒消息,我可以看到他们已在数据库中删除。如果我导航回仪表板并返回学生列表,CardView 就会消失。奇怪的。
每次删除后,我都尝试再次调用 onStart ,但这没有帮助。有任何想法吗?
我的活动:
public class StudentListActivity extends AppCompatActivity {
//firebase auth
private FirebaseAuth mAuth;
//public variables
public String currentUserAccount;
public String teacherAccountNav = "Teacher";
public String currentUserId;
//recyclerView variables
DatabaseReference ref;
ArrayList<Student> list;
RecyclerView recyclerView;
SearchView searchView;
@RequiresApi(api = Build.VERSION_CODES.KITKAT)
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_student_list);
//get current user
mAuth = FirebaseAuth.getInstance();
FirebaseUser user = mAuth.getCurrentUser();
//assert current user is not null and get current users id
assert user != null;
currentUserId = user.getUid();
//getting firebase reference of current users students
ref = FirebaseDatabase.getInstance().getReference().child("students").child(currentUserId);
//initialise views
recyclerView = findViewById(R.id.rv);
recyclerView.setHasFixedSize(true);
searchView = findViewById(R.id.searchView);
}
@Override
protected void onStart() {
super.onStart();
if(ref != null){
ref.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
//add students from firebase to an array list
if(dataSnapshot.exists()){
list = new ArrayList<>();
for(DataSnapshot ds : dataSnapshot.getChildren()){
list.add(ds.getValue(Student.class));
}
//sort by name
Collections.sort(list, Student.myName);
//make recycler view
recyclerView.setLayoutManager(new LinearLayoutManager(StudentListActivity.this));
StudentAdapterClass studentAdapterClass = new StudentAdapterClass(list);
recyclerView.setAdapter(studentAdapterClass);
//click listeners for buttons
studentAdapterClass.setOnItemClickListener(new StudentAdapterClass.OnItemClickListener() {
@Override
public void onUpdateClick(int position) {
//handle update click in here
Student student = list.get(position);
//show update dialog here
showUpdateDialog(student.getStudentId(), student.getStudentName(), student.getStudentEmail());
}
@Override
public void onDeleteClick(int position){
//handle delete click in here
Student student = list.get(position);
//show delete dialog here
showDeleteDialog(student.getStudentId());
}
});
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
Toast.makeText(StudentListActivity.this, databaseError.getMessage(), Toast.LENGTH_SHORT).show();
}
});
}//if
}
//dialog box for deleting student
private void showDeleteDialog(final String studentId){
AlertDialog.Builder dialogBuilder = new AlertDialog.Builder(this);
LayoutInflater inflater = getLayoutInflater();
//dialog XML
final View dialogView = inflater.inflate(R.layout.delete_student_dialog, null);
dialogBuilder.setView(dialogView);
final ImageButton buttonNo = dialogView.findViewById(R.id.imageButtonNo);
final ImageButton buttonYes = dialogView.findViewById(R.id.imageButtonYes);
final AlertDialog alertDialog = dialogBuilder.create();
alertDialog.show();
buttonNo.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
alertDialog.dismiss();
}
});
buttonYes.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
deleteStudent(studentId);
alertDialog.dismiss();
}
});
}
//delete student method
private void deleteStudent(String id){
//get current user
mAuth = FirebaseAuth.getInstance();
FirebaseUser user = mAuth.getCurrentUser();
//assert current user is not null and get current users id
assert user != null;
currentUserId = user.getUid();
DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference("students").child(currentUserId).child(id);
databaseReference.removeValue();
Toast.makeText(this, "Student Deleted", Toast.LENGTH_LONG).show();
//clear and get new list
onStart();
}
我的适配器:
public class StudentAdapterClass extends RecyclerView.Adapter<StudentAdapterClass.MyViewHolder> {
private ArrayList<Student> list;
private OnItemClickListener mListener;
public interface OnItemClickListener{
//click method for update button
void onUpdateClick(int position);
//click method for delete button
void onDeleteClick(int position);
}
public void setOnItemClickListener(OnItemClickListener listener){
mListener = listener;
}
public StudentAdapterClass(ArrayList<Student> list){
this.list = list;
}
@NonNull
@Override
public MyViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.card_holder, viewGroup, false);
return new MyViewHolder(view, mListener);
}
@Override
public void onBindViewHolder(@NonNull MyViewHolder myViewHolder, int i) {
myViewHolder.name.setText(list.get(i).getStudentName());
myViewHolder.email.setText(list.get(i).getStudentEmail());
}
@Override
public int getItemCount() {
return list.size();
}
static class MyViewHolder extends RecyclerView.ViewHolder {
TextView name, email;
ImageButton update, delete;
MyViewHolder(@NonNull View itemView, final OnItemClickListener listener) {
super(itemView);
name = itemView.findViewById(R.id.studentName);
email = itemView.findViewById(R.id.studentEmail);
update = itemView.findViewById(R.id.updateButton);
delete = itemView.findViewById(R.id.deleteButton);
//update click listener
update.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (listener != null){
int position = getAdapterPosition();
if(position != RecyclerView.NO_POSITION){
listener.onUpdateClick(position);
}
}
}
});
delete.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (listener != null){
int position = getAdapterPosition();
if(position != RecyclerView.NO_POSITION){
listener.onDeleteClick(position);
}
}
}
});
}
}
解决方案
每次 RecyclerView 数据发生变化,都必须调用适配器方法notifyDataSetChanged()
,否则 RecyclerView 无法正确刷新。您可以像这样在方法内部调用它deleteStudent()
。
recyclerView.getAdapter().notifyDataSetChanged()
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