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我想从Firebase获取一个字符串列表,并且在检索完所有数据后才会更新我的UI。目前我正在使用片段类中的以下代码来实现此目的。在Firebase中获取上下文valueEventListener
taskList = new ArrayList<>();
mDatabase.child("users").child(mUserId).child("items").orderByChild("id").addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot){
for(DataSnapshot childSnapshot : dataSnapshot.getChildren()){
taskList.add(new Pair<>((long) childSnapshot.child("id").getValue(),(String) childSnapshot.child("title").getValue()));
}
//update UI
setupListRecyclerView();
}
@Override
public void onCancelled(DatabaseError firebaseError){
throw firebaseError.toException();
}
});
的setupListRecyclerView工作,如果放在valueEventListener之外,但是如果放在我得到它"Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference"
错误。但是,如果我将它放在侦听器之外,它将在检索Firebase数据之前更新UI,这样我就会丢失。
这里是setupListRecyclerView的样子:
private void setupListRecyclerView() {
mDragListView.setLayoutManager(new LinearLayoutManager(getContext()));
ItemAdapter listAdapter = new ItemAdapter(taskList, R.layout.list_item, R.id.image, false);
mDragListView.setAdapter(listAdapter, true);
mDragListView.setCanDragHorizontally(false);
mDragListView.setCustomDragItem(new MyDragItem(getContext(), R.layout.list_item));
}
private static class MyDragItem extends DragItem {
MyDragItem(Context context, int layoutId) {
super(context, layoutId);
}
@Override
public void onBindDragView(View clickedView, View dragView) {
CharSequence text = ((TextView) clickedView.findViewById(R.id.text)).getText();
((TextView) dragView.findViewById(R.id.text)).setText(text);
dragView.findViewById(R.id.item_layout).setBackgroundColor(dragView.getResources().getColor(R.color.list_item_background));
}
}
谢谢! 'listAdapter.notifyDataSetChanged()'起作用! –