这个问题使我发疯。到目前为止，我已经尝试了20种不同的方法。因此，让我们看看这里是否有人可以帮助我。
我正在使用RecyclerView制作将数据存储在Firebase中的待办事项列表APP。
该应用程序有一个TasksActivity，其中所有任务都显示在RecyclerView中。我有一个转到“任务创建”对话框的按钮。我可以创建任务，然后将它们显示在RecyclerView（“任务活动”）中，并在firebase中对其进行更新，没有任何问题。我可以关闭该APP并稍后再返回，并且一切正常，当我加载它时，所有条目都会再次出现在该应用中。我还可以滑动删除一个条目，并且该条目也会从firebase的数据库中删除。
问题是，当我创建一个任务而没有关闭应用程序时，我尝试删除刚创建的任务。它不允许我这样做。当我创建一个新任务，并在关闭应用程序之前立即将其删除时，它将再次出现。但是，如果我随后关闭该应用程序并再次加载它，则可以正常删除该条目，但是如果我处于创建该条目的同一会话中，则无法删除它。
我正在使用一些Log.d参数来查看其变化。我出于各种原因认为问题是OnDataChange()。但是到目前为止，我还没有找到问题的根源。这是TaskActivity类，在此之后，我将粘贴TasksCreation（我认为没有必要粘贴适配器）。
public class TasksActivity extends AppCompatActivity {
DatabaseReference reference;
RecyclerView myTasks;
ArrayList<TaskItems> myTasksList;
TasksAdapter tasksAdapter;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_tasks);
myTasks = findViewById(R.id.my_tasks); // RecyclerView that I defined as part of the layout. This is the id of it
myTasks.setLayoutManager(new LinearLayoutManager(this,LinearLayoutManager.VERTICAL,false));
myTasksList = new ArrayList<>();
Button openCreateTask = findViewById(R.id.openCreateTask);
tasksAdapter = new TasksAdapter(this,myTasksList);
myTasks.setAdapter(tasksAdapter);
new ItemTouchHelper(itemTouchHelper).attachToRecyclerView(myTasks);
openCreateTask.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent_task = new Intent(getApplicationContext(), TasksCreation.class);
startActivity(intent_task);
}
});
reference = FirebaseDatabase.getInstance().getReference().child("MotApp"); // Name of the App in the database .child("MotApp")
reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) { // It gets the info from the database
Log.d("data Changed called", "onDataChange: is called");
Log.d("whatever", "onDataChange BEGIN Array of myTasksList size is "+myTasksList.size());
myTasksList.clear(); // Added later to avoid duplication
for(DataSnapshot elements: dataSnapshot.getChildren()){
TaskItems p = elements.getValue(TaskItems.class);
myTasksList.add(p);
}
tasksAdapter.notifyDataSetChanged(); // If this is put outside of onDataChange, it displays a blank list.
Log.d("whatever", "onDataChange END Array of myTasksList size is "+myTasksList.size());
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
Toast.makeText(getApplicationContext(), "No data", Toast.LENGTH_SHORT).show();
}
});
}
ItemTouchHelper.SimpleCallback itemTouchHelper = new ItemTouchHelper.SimpleCallback(0,ItemTouchHelper.RIGHT) {
@Override
public boolean onMove(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, @NonNull RecyclerView.ViewHolder target) {
return false;
}
@Override
public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder, int direction) {
int position = viewHolder.getAdapterPosition();
Log.d("ARRAY SIZE", "onSwiped BEGIN Array of myTasksList size is "+myTasksList.size());
String key = myTasksList.get(position).getKey();
reference= FirebaseDatabase.getInstance().getReference().child("MotApp").child(key);
Toast.makeText(getApplicationContext(),"This is key "+key,Toast.LENGTH_LONG).show();
reference.removeValue();
myTasksList.remove(position);
tasksAdapter.notifyItemRemoved(position);
Log.d("ARRAY SIZE", "onSwiped END Array of myTasksList size is "+myTasksList.size());
}
};
}
这是针对TasksCreation活动的：
public class TasksCreation extends AppCompatActivity {
DatabaseReference referenceCreation;
ArrayList<String> list;
EditText taskName;
EditText taskDescr;
Button selectDates;
TextView taskDate;
Button createTask;
Button cancel;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_tasks_creation);
taskName = findViewById(R.id.et_TaskName);
taskDescr = findViewById(R.id.et_TaskDescr);
selectDates = findViewById(R.id.selectDates);
taskDate= findViewById(R.id.tv_Dates);
createTask = findViewById(R.id.createTask);
cancel = findViewById(R.id.cancelButton);
createTask.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (!TextUtils.isEmpty(taskName.getText()) && !TextUtils.isEmpty(taskDate.getText())) {
referenceCreation = FirebaseDatabase.getInstance().getReference().child("MotApp").push(); //saves it with custom key created by Firebase
final String key = referenceCreation.getKey();
referenceCreation.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
dataSnapshot.getRef().child("key").setValue(key);
dataSnapshot.getRef().child("taskTitle").setValue(taskName.getText().toString());
dataSnapshot.getRef().child("taskDescription").setValue(taskDescr.getText().toString());
dataSnapshot.getRef().child("taskDate").setValue(taskDate.getText().toString());
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
Intent intent = new Intent(getApplicationContext(), TasksActivity.class);
startActivity(intent);
} else{
Toast.makeText(getApplicationContext(), "You haven't filled all the fields", Toast.LENGTH_SHORT).show();
}
}
});
cancel.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(getApplicationContext(), TasksActivity.class);
startActivity(intent);
}
});
selectDates.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
createAlertDialogue();
}
});
}
private void createAlertDialogue(){
list = new ArrayList<String>();
AlertDialog.Builder builder = new AlertDialog.Builder(this,R.style.MyDialogTheme);
builder.setTitle("Select days");
builder.setMultiChoiceItems(R.array.Days, null, new DialogInterface.OnMultiChoiceClickListener() {
@Override
public void onClick(DialogInterface dialog, int which, boolean isChecked) {
String arr[] = getResources().getStringArray(R.array.Days);
if(isChecked){
list.add(arr[which]);
}else if(list.contains(arr[which])){
list.remove(arr[which]);
}
}
});
builder.setPositiveButton("Save", new DialogInterface.OnClickListener() {
String data = "";
@Override
public void onClick(DialogInterface dialog, int which) {
for(String elements: list){
elements = elements.substring(0,3);
data= elements+" "+data;
}
taskDate.setText(data);
}
});
builder.create();
builder.show();
}
}
我真的很感谢这个问题。
非常感谢
P：S：这是TaskAdapter的代码（忽略一周中的一天部分仅是我评论的部分代码）
public class TasksAdapter extends RecyclerView.Adapter<TasksAdapter.MyViewHolder> { // V 1.3 added OnClickListener
Context context;
ArrayList<TaskItems> tasks;
DatabaseReference reference;
SimpleDateFormat sdf = new SimpleDateFormat("EEEE");
Date d = new Date();
final String dayOfTheWeek = sdf.format(d).substring(0,3);
public TasksAdapter(Context context, ArrayList<TaskItems> tasks) {
this.context = context;
this.tasks = tasks;
}
public class MyViewHolder extends RecyclerView.ViewHolder { // V1.3 Added implements View.OnClickListener
TextView taskTitle;
TextView taskDate;
TextView taskDescription;
CheckBox taskCheckBox;
ConstraintLayout constraintLayout; // Added to change background of each RecyclerView item.
public MyViewHolder(@NonNull View itemView) {
super(itemView);
taskTitle = itemView.findViewById(R.id.taskTitle);
taskDate = itemView.findViewById(R.id.taskDate);
taskDescription = itemView.findViewById(R.id.taskDescription);
taskCheckBox = itemView.findViewById(R.id.taskCheckBox);
constraintLayout = (ConstraintLayout) itemView.findViewById(R.id.item_task_layout);
itemView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
int pos = getAdapterPosition();
// if(pos != RecyclerView.NO_POSITION){//Checks if item still exists
TaskItems clickedDataItem = tasks.get(pos);
Toast.makeText(v.getContext(), "You clicked " + clickedDataItem.getTaskTitle(), Toast.LENGTH_SHORT).show();
// }
}
});
}
}
@NonNull
@Override
public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) { // standard code for onCreateViewHolder
return new MyViewHolder(LayoutInflater.from(context).inflate(R.layout.item_task,parent,false));
}
@Override
public void onBindViewHolder(final @NonNull MyViewHolder holder, final int position) { // This method is called once for each item on the list.
holder.taskTitle.setText(tasks.get(position).getTaskTitle());
holder.taskDescription.setText(tasks.get(position).getTaskDescription());
holder.taskDate.setText(tasks.get(position).getTaskDate());
holder.taskCheckBox.setChecked(tasks.get(position).isChecked());
holder.taskCheckBox.setTag(tasks.get(position).getKey());
holder.taskCheckBox.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
FirebaseDatabase database = FirebaseDatabase.getInstance();
String post = (String) holder.taskCheckBox.getTag();
Toast.makeText(context,"This is checkbox number: "+post,Toast.LENGTH_SHORT).show(); // Working Well. //change for new logic
reference = database.getReference("MotApp").child(post);
boolean checkboxStatus = holder.taskCheckBox.isChecked();
Log.d("Checked", "onClick: The taskcheckbox checked is "+holder.taskCheckBox.isChecked());
TaskItems value = new TaskItems(tasks.get(position).getKey(),tasks.get(position).getTaskTitle(), tasks.get(position).getTaskDate(),tasks.get(position).getTaskDescription(),checkboxStatus);
reference.setValue(value);
Toast.makeText(context,"This is a checkbox belonging to item "+tasks.get(position).getTaskTitle(),Toast.LENGTH_LONG).show();
}
});
}
@Override
public int getItemCount() { //tells the adapter the size . if it's zero then it won't create anything
return tasks.size();
}
}
答案 0 :(得分：1)
从RecyclerView返回时，您需要在TasksActivity中重建TasksCreation数据；这是因为onCreate()的{{1}}回调仅在您打开应用程序时被调用；这就是为什么只有在关闭应用程序并重新打开后才能删除的原因。
从TasksActivity返回时不会调用onCreate()，因为当您从TasksCreate转移到TasksActivity时，TasksCreation不会被破坏，但只是停止了，因此当您返回TasksActivity时，它将开始并恢复；因此，请将您在TasksActivity上的代码转移到onCreate()上，以便使用最新更改来更新列表。
因此，将您的onResume()更改为下面的
TasksActivity答案 1 :(得分：1)
我终于找到了解决方法。
首先，我在TaskActivity和TaskCreation中使用addListenerforSingleValueEvent更改了所有addValueEventListener。有了addValueEventListener，我意识到每次创建一个新任务时都会造成多个循环，这会导致各种问题。
我还更改了在TaskCreation中设置startIntent的方式。我最初是在Listener块之后设置的。但是onDataChange的异步特性使得每次我加载意图时，更新的信息都不会与刚刚添加的新任务一起建立。
通过将其放入onDataChange中，此问题已解决。我已经进行了几次测试，现在可以正常工作了。
我浪费了很多天试图解决这个问题。但是我在此过程中学到了很多教训。所以我想他们并没有浪费时间:)。
感谢所有努力帮助我解决此问题的人。