片段中的列表视图不是从firebase填充的，但我可以将数据保存到可能的firebase DB
我有一个MainActivity.Java类，它使用视图分页程序来呈现片段。其中一个片段名为DashBoardFrag，它将从我的firebase DB中提取数据并将其填充到列表视图中。目前，我可以发送数据并将其保存到firebas，但无法检索。检索应该在DashBoardFrag加载或显示到user.When时发生。我运行我的应用程序时，它没有崩溃，但仍然没有显示任何内容。这是我的DashBoardFrag片段中的onCreateView method
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the fragment_dash_board for this fragment
View rootView = inflater.inflate(R.layout.fragment_dash_board, container, false);
newsListView = (ListView) rootView.findViewById(R.id.newslist_view);
dbref = FirebaseDatabase.getInstance().getReference();
dbOperationsHelper = new DBOperationsHelper(dbref);
/**
* SET ADAPTER
*/
//dbAdapter = new DBAdapter(getActivity().getApplicationContext(),dbOperationsHelper.retrieveNews());
arrayAdapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1,dbOperationsHelper.retrieveNews());
//Toast.makeText(getActivity().getApplicationContext(), "MUST NOT BE EMPTY", Toast.LENGTH_SHORT).show();
newsListView.setAdapter(dbAdapter);
return rootView;
}这是我的DBOperationsHelper类
public class DBOperationsHelper {
DatabaseReference dbref;
Boolean saved;
ArrayList<String> newsArraylist = new ArrayList<>();
public DBOperationsHelper(DatabaseReference db){
this.dbref = db;
}
public Boolean save(DBModel news){
if(news == null){
saved = false;
}else{
try {
dbref.child("DBModel").push().setValue(news);
saved = true;
} catch (DatabaseException e) {
e.printStackTrace();
saved = false;
}
}
return saved;
}
private void fetchData(DataSnapshot dataSnapshot){
newsArraylist.clear();
for(DataSnapshot ds : dataSnapshot.getChildren()){
String news = ds.getValue(DBModel.class).getNewsHead();
newsArraylist.add(news);
}
}
/**
* RETRIEVE NEWS
*/
public ArrayList<String> retrieveNews(){
dbref.addChildEventListener(new ChildEventListener() {
@Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
fetchData(dataSnapshot);
}
@Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
fetchData(dataSnapshot);
}
@Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
@Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
return newsArraylist;
}
}这是我的DBModel class
public class DBModel {
boolean bool;
String name, email, username, pass, newsHead, newsBody;
public void setIsLogin(boolean bl){
this.bool = bl;
}
public boolean getIsLogin(){
return this.bool;
}
public void setEmail(String email){
this.email = email;
}
public String getEmail(){
return this.email;
}
public void setUsername(String username){
this.username = username;
}
public String getUsername(){
return this.username;
}
public void setPass(String pass){
this.pass = pass;
}
public String getPass(){
return this.pass;
}
public void setNewsHead(String nws_name){
this.newsHead = nws_name;
}
public String getNewsHead() {
return newsHead;
}
public void setNewsBody(String newsBody) {
this.newsBody = newsBody;
}
public String getNewsBody() {
return newsBody;
}
}回答 4
Stack Overflow用户
发布于 2016-10-04 18:55:33
最后，我设法使用FirebaseRecyclerAdapter填充我的回收器(从使用列表视图更改为回收器视图)。
这就是我所做的。
1.针对我要显示和检索的详细信息，更改我的 setters 对象类，使其具有 getters 和setters，如下所示
public class NewsModel {
String email, username, pass, newsHead, newsBody;
public NewsModel() {
}
public NewsModel(String newsHead, String newsBody) {
this.newsHead = newsHead;
this.newsBody = newsBody;
}
public String getNewsHead() {
return newsHead;
}
public void setNewsHead(String nws_name){
this.newsHead = nws_name;
}
public String getNewsBody() {
return newsBody;
}
public void setNewsBody(String newsBody) {
this.newsBody = newsBody;
}
}2.通过创建一个内部静态类来编辑我的片段，该类扩展了我用来设置文本字段的值的 RecyclerViewHolder**，，如下所示**
DatabaseReference dbref;
FirebaseRecyclerAdapter<NewsModel,NewsModelVH> firebasenewsRecycleAdapter ;
RecyclerView newsrecyclerView;
LinearLayoutManager nwlinearLayoutManager;
ArrayList<NewsModel> newsArraylist = new ArrayList<>();
public static class NewsModelVH extends RecyclerView.ViewHolder{
public TextView newsHead, newsBody;
public NewsModelVH(View itemView) {
super(itemView);
this.newsHead = (TextView) itemView.findViewById(R.id.listview_item_title);
this.newsBody = (TextView) itemView.findViewById(R.id.listview_item_short_description);
}
}// End NewsModelVH class
public static final String NEWS= "NewsModel";并将我的onCreateView方法编辑为使用FirebaseRecyclerAdapter，该方法使用DBModel class DatabaseReference和RecyclcerViewHolder，如下所示
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the fragment_dash_board for this fragment
View rootView = inflater.inflate(R.layout.fragment_news_rv, container, false);
newsrecyclerView =(RecyclerView) rootView.findViewById(R.id.rv_noticeboard);
nwlinearLayoutManager = new LinearLayoutManager(getActivity());
nwlinearLayoutManager.setStackFromEnd(true);
dbref = FirebaseDatabase.getInstance().getReference();
firebasenewsRecycleAdapter = new FirebaseRecyclerAdapter<NewsModel, NewsModelVH>(
NewsModel.class,
R.layout.fragment_dashboard_imagetext,
NewsModelVH.class,
dbref.child(NEWS)) {
@Override
protected void populateViewHolder(NewsModelVH viewHolder, NewsModel model, int position) {
viewHolder.newsHead.setText(model.getNewsHead());
viewHolder.newsBody.setText(model.getNewsBody());
}
};
firebasenewsRecycleAdapter.registerAdapterDataObserver(new RecyclerView.AdapterDataObserver(){
@Override
public void onItemRangeInserted(int positionStart, int itemCount){
super.onItemRangeInserted(positionStart, itemCount);
int newsCount = firebasenewsRecycleAdapter.getItemCount();
int lastVisiblePosition = nwlinearLayoutManager.findLastVisibleItemPosition();
if(lastVisiblePosition == -1 || (positionStart>= (newsCount -1) && lastVisiblePosition == (positionStart -1))){
newsrecyclerView.scrollToPosition(positionStart);
}
}
});
newsrecyclerView.setLayoutManager(nwlinearLayoutManager);
newsrecyclerView.setAdapter(firebasenewsRecycleAdapter);
/**
* SET ADAPTER
*/
ProgressBar newsprogressBar = (ProgressBar) rootView.findViewById(R.id.progress_bar);
newsprogressBar.setVisibility(View.VISIBLE);
Log.v("RETRIEVE", " dbOperationsHelper.retrieveNews() NEWS=" + dbref);
return rootView;
}不过，有一件事仍然困扰着我，那就是为什么要显示数据，而我既没有使用dbref.addValueEventListener(new ValueEventListener()也没有使用ref.addChildEventListener(new ChildEventListener()
嗯，有些事情告诉我，未来可能会限制我实现一些things...not确定的东西，但当那个时候到来的时候，我就会知道了。但如果有人对此有解释，也可以分享信息。
否则，希望这能帮助别人，这样你就不会被困住两天，在不同的适配器(ArrayAdapter，ArrayList，CustomeAdapter，FirebaseListAdapter，最后是FirebaseRecyclerAdapter)之间切换来找到解决方案。
Stack Overflow用户
发布于 2016-10-04 01:00:21
经过两天的尝试，我设法在列表视图上检索了数据，唯一改变的是我不使用ArrayAdapters，而是使用了我的自定义适配器。在onCreateView method内部我改变了
arrayAdapter = new ArrayAdapter<String>(getActivity(),android.R.layout.simple_list_item_1,dbOperationsHelper.retrieveNews());
至
dbAdapter = newDBAdapter(getActivity().getApplicationContext(), dbOperationsHelper.retrieveNews());
在DBOperationsHelper中，我将ArrayList更改为获取DBModel对象而不是string对象，如下所示
ArrayList<String> newsArraylist = new ArrayList<>();
至
ArrayList<DBModel> newsArraylist = new ArrayList<>();
我还将fetchData method更改为如下所示
private void fetchData(DataSnapshot dataSnapshot){
newsArraylist.clear();
for(DataSnapshot ds : dataSnapshot.getChildren()){
DBModel news = ds.getValue(DBModel.class);
newsArraylist.add(news);
Log.v("FIREBASE RETRIEVE", "index=" + ds.getValue(DBModel.class));
}
}但现在的问题是，当片段第一次启动时，它没有显示任何内容，但当我向firebase数据库添加新记录，然后对片段进行多次刷新时，数据最终出现并以一种奇怪的方式显示，如下图所示。有谁知道发生了什么吗？
Stack Overflow用户
发布于 2016-10-04 01:07:49
使用firebase ui，添加依赖项中的编译'com.firebaseui:firebase-ui-database:0.4.1‘，然后遵循此https://firebaseui.com/docs/android/index.html
https://stackoverflow.com/questions/39806252
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