我的自定义适配器，当我添加任务时，除非或直到它重新启动应用程序或在片段之间切换，否则getitemcount（）的值不会增加。除非我也执行相同的步骤，否则itemtouchelper会更新UI。我正在使用activityresult方法更新适配器。
public class CustomAdapterReminders extends RecyclerView.Adapter<CustomAdapterReminders.MyRecyclerView2> implements ItemMoveCallback.ItemTouchHelperContractReminder{
private List<String[]> customListView;
private String[] mRecentlyDeletedItem;
private int mRecentlyDeletedItemPosition;
private View snackbarView;
private static final String dueDatedTime = "Due on: ";
private Context context;
public int positionAfterNewTAsk;
public void setPositionAfterNewTAsk(int positionAfterNewTAsk) {
this.positionAfterNewTAsk = positionAfterNewTAsk;
}
public CustomAdapterReminders(List<String[]> customListView) {
this.customListView = customListView;
Log.d("Item count" , String.valueOf(getItemCount()));
}
public CustomAdapterReminders() {
}
@NonNull
@Override
public MyRecyclerView2 onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
context = parent.getContext();
LayoutInflater inflater = LayoutInflater.from(parent.getContext());
View itemView = inflater.inflate(R.layout.recycler_item_reminders,parent,false);
MyRecyclerView2 viewHolder = new MyRecyclerView2(itemView);
snackbarView = parent.getRootView();
return viewHolder;
}
@Override
public void onBindViewHolder(@NonNull MyRecyclerView2 holder, int position) {
String[] temp = customListView.get(position);
holder.taskText.setText(temp[1]);
holder.taskDate.setText(dueDatedTime + temp[2]);
}
public void changeData(){
notifyDataSetChanged();
}
@Override
public int getItemCount() {
return customListView.size();
}
@Override
public void onRowMoved(int fromPosition, int toPosition) {
try {
if (fromPosition < toPosition) {
for (int i = fromPosition; i < toPosition; i++) {
Collections.swap(customListView, i, i + 1);
}
} else {
for (int i = fromPosition; i > toPosition; i--) {
Collections.swap(customListView, i, i - 1);
}
}
notifyItemMoved(fromPosition, toPosition);
} catch (Exception ex) {
Log.d("TAG", "Error in moving items");
}
}
@Override
public void onRowSelected(MyRecyclerView2 myViewHolder) {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
myViewHolder.rowView.setBackgroundResource(R.drawable.border);
}
}
@Override
public void onItemDismiss(int position) {
Log.d("Position", String.valueOf(position) +"Count"+ String.valueOf(getItemCount()) + "Pos" + positionAfterNewTAsk);
String[] deleteIndex = customListView.get(position);
mRecentlyDeletedItemPosition = position;
mRecentlyDeletedItem = customListView.get(position);
customListView.remove(position);
TaskDBHelper taskDBHelper = new TaskDBHelper(context);
final Handler handler = new Handler();
showUndoSnackbar();
handler.postDelayed(() -> taskDBHelper.DeleteFromReminders(deleteIndex[0]), 3000);
notifyItemRemoved(position);
notifyItemRangeChanged(position,getItemCount());
positionAfterNewTAsk = 0;
}
@Override
public void onRowClear(MyRecyclerView2 myViewHolder) {
myViewHolder.rowView.setBackgroundResource(R.drawable.seleted_border);
}
private void undoDelete() {
customListView.add(mRecentlyDeletedItemPosition,
mRecentlyDeletedItem);
notifyItemInserted(mRecentlyDeletedItemPosition);
notifyItemRangeChanged(mRecentlyDeletedItemPosition,getItemCount());
}
private void showUndoSnackbar() {
Snackbar.make(snackbarView, "Task deleted", Snackbar.LENGTH_LONG)
.setAction("Undo", v -> undoDelete()).show();
}
public class MyRecyclerView2 extends RecyclerView.ViewHolder {
TextView taskText, taskDate;
View rowView;
private MyRecyclerView2(@NonNull View itemView) {
super(itemView);
rowView = itemView;
taskText = itemView.findViewById(R.id.reminderstextView);
taskDate = itemView.findViewById(R.id.remindersDateView);
}
}
}
> **
**
public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
remindersViewModel = ViewModelProviders.of(this).get(RemindersViewModel.class);
View root = inflater.inflate(R.layout.fragment_home, container, false);
OneSignal.startInit(this.getContext())
.inFocusDisplaying(OneSignal.OSInFocusDisplayOption.Notification)
.unsubscribeWhenNotificationsAreDisabled(true)
.init();
OneSignal.startInit(this.getContext())
.setNotificationReceivedHandler(new ExampleNotificationReceivedHandler())
.inFocusDisplaying(OneSignal.OSInFocusDisplayOption.Notification)
.unsubscribeWhenNotificationsAreDisabled(true)
.init();
setAdapter();
FloatingActionButton fab = root.findViewById(R.id.floatingActionButton);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent addTask = new Intent(getActivity(), AddTask.class);
startActivityForResult(addTask,ADD_TASK);
}
});
return root;
}
@Override
public void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if(requestCode == 1) {
refreshUI();
}
}
@Override
public void onResume() {
super.onResume();
setAdapter();
}
private void refreshUI() {
setAdapter();
adapter.changeData();
}
private void setAdapter() {
try {
taskDBHelper = new TaskDBHelper(this.getContext());
try {
taskList = taskDBHelper.browseReminders();
adapter = new CustomAdapterReminders(taskList);
}
catch (Exception e){
Log.d(TAG, "Exception in browsing");
}
staggaggeredGridLayoutManager = new StaggeredGridLayoutManager(2, 1);
recyclerViewItems = getActivity().findViewById(R.id.rv);
recyclerViewItems.setLayoutManager(staggaggeredGridLayoutManager);
recyclerViewItems.setAdapter(adapter);
adapter.changeData();
ItemMoveCallback itemMoveCallback = new ItemMoveCallback();
ItemTouchHelper.Callback callback = new ItemMoveCallback(adapter);
touchHelper = new ItemTouchHelper(callback);
touchHelper.attachToRecyclerView(recyclerViewItems);
} catch (NullPointerException ex) {
Log.d(TAG, "Exception in setAdapter");
}
}
@Override
public void requestDrag(RecyclerView.ViewHolder viewHolder) {
touchHelper.startDrag(viewHolder);
}
相反，当用户决定添加任务时，将相应的String[]对象直接输入到customListView中，并调用通知数据集已更改。同时执行一条命令，将相同的数据插入数据库。
因为您正在从主线程修改适配器，所以所有的事情都会依次发生，并且在进行插入操作之前，您不会冒着读取数据库的风险。
另一个选择是，您使用Room框架通过LiveData和onChanged侦听器来处理数据库。这意味着需要花费大量精力来阅读文献，但是会议室框架确实可以为您提供很多简化代码的方法]