I have an Activity which contains different items, one of those item is ListView.
I created a custom list adapter and sending to it a json array.
The data for the list arrives from the server.
The list purpose is to make comments list. I allowed the user to insert
a comment and then I show it in the ListView.
When I have some items in the list it works, and the items are shown.
The problem is when listview is empty and the user post a comment.
I see that that data is changed but I don't see the item, means the list is not refreshed..
So I tried to add to the listview an empty view but it doesn't work.
Here is an updated code: (UPDATE)
if (!s.isEmpty() && !s.equals("{}")) {
try {
if (commentsListAdapter == null) {
commentsList.setEmptyView(findViewById(R.id.dummy));
commentsListAdapter = new CommentsListAdapter(PostView.this);
}
JSONObject resObj = new JSONObject(s);
list.add(resObj);
commentsListAdapter.setDataSet(list);
cmntTxt.setText("");
inputManager.hideSoftInputFromWindow(getCurrentFocus().getWindowToken(),
InputMethodManager.HIDE_NOT_ALWAYS);
commentCounter.setText(Integer.toString(list.size()));
} catch (JSONException e) {
e.printStackTrace();
}
}
And inside the Adapter I have this function:
public void setDataSet(List<JSONObject> list){
commentsList = list;
notifyDataSetChanged();
}
But the problem is not fixed..
I notice the code list.add(resObj) appears after new CommentsListAdapter when the list is empty and appears before new CommentsListAdapter when the list is NOT empty.
I suspect the Adapter CommentsListAdapter is not using the object list for the data storage. In that case, you need to make a public method in the adapter to make updates. Another words, the adapter is using another object for data storage.
It may help to post the code for CommentsListAdapter also. But I hope I am correct about my statements.
I hope that is clear...
Please change the following code:
public void setDataSet(List<JSONObject> list){
commentsList = list;
notifyDataSetChanged();
}
to :
private List<JSONObject> commentsList = new ArrayList<>();
public void setDataSet(List<JSONObject> list){
commentsList.clear();
commentsList.addAll(list);
notifyDataSetChanged();
}
And use commentsList for all other methods in your adapter. This is a better way for notifyDataSetChanged() to work.
Hope it helps! :)
if you are adding your comment from the outside i.e from activity and not from adapter than whenever you set the adapter do this.
youradapterobject.notifyDataSetChanged();
and dont do commentsListAdapter == null than setemptyview
it automatically sets the emptyview if its null
correct usage
list.setEmptyView(findViewById(R.id.erromsg));
Related
This question already has answers here:
How to update RecyclerView Adapter Data
(16 answers)
Closed 5 years ago.
When I have to use a classic adapter with a ListView, I update my data in the ListView like this:
myAdapter.swapArray(data);
public swapArray(List<Data> data) {
clear();
addAll(data);
notifyDataSetChanged();
}
I would like to know what is the best practice for a RecyclerView. Because in a RecyclerView adapter you can't do a clear and addAll as in ListView.
So I tried just with a notifyDataSetChanged, but it didn't work.
Then I tried with a swapAdapter on my view:
List<Data> data = newData;
MyRecyclerAdapter adapter = new MyRecyclerAdapter(data);
// swapAdapter on my recyclerView (instead of a .setAdapter like with a classic listView).
recyclerViewList.swapAdapter(adapter, false);
But with this last solution, I still have to create a new instance of my adapter and I feel like it's not the best solution. I should be able just to change my data without a new MyRecyclerAdapter.
RecyclerView's Adapter doesn't come with many methods otherwise available in ListView's adapter. But your swap can be implemented quite simply as:
class MyRecyclerAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
List<Data> data;
...
public void swap(ArrayList<Data> datas)
{
data.clear();
data.addAll(datas);
notifyDataSetChanged();
}
}
Also there is a difference between
list.clear();
list.add(data);
and
list = newList;
The first is reusing the same list object. The other is dereferencing and referencing the list. The old list object which can no longer be reached will be garbage collected but not without first piling up heap memory. This would be the same as initializing new adapter everytime you want to swap data.
#inmyth's answer is correct, just modify the code a bit, to handle empty list.
public class NewsAdapter extends RecyclerView.Adapter<...> {
...
private static List mFeedsList;
...
public void swap(List list){
if (mFeedsList != null) {
mFeedsList.clear();
mFeedsList.addAll(list);
}
else {
mFeedsList = list;
}
notifyDataSetChanged();
}
I am using Retrofit to fetch the list, on Retrofit's onResponse() use,
adapter.swap(feedList);
DiffUtil can the best choice for updating the data in the RecyclerView Adapter which you can find in the android framework. DiffUtil is a utility class that can calculate the difference between two lists and output a list of update operations that converts the first list into the second one.
Most of the time our list changes completely and we set new list to RecyclerView Adapter. And we call notifyDataSetChanged to update adapter. NotifyDataSetChanged is costly. DiffUtil class solves that problem now. It does its job perfectly!
Found following solution working for my similar problem:
private ExtendedHashMap mData = new ExtendedHashMap();
private String[] mKeys;
public void setNewData(ExtendedHashMap data) {
mData.putAll(data);
mKeys = data.keySet().toArray(new String[data.size()]);
notifyDataSetChanged();
}
Using the clear-command
mData.clear()
is not nessescary
In one of my activity I have EditText, Submit Button and a ListView. The data of ListView are retrived from database. To retrive data from database and adapt to ListView I used the following code.
private void loadList() {
mylist = new ArrayList<HashMap<String, Object>>();
mylist.clear();
List<Data> catDesc = dbhelper.getCatMasterDesc(id);
ArrayAdapter<Data> adapter = new SimpleAdapter(getApplicationContext(), R.layout.list, catDesc);
lv1 = (ListView) findViewById(R.id.masListView1);
lv1.setAdapter(adapter);
}
And i call this method every time whenever I update the database to show updated listview.
String str = category.getText().toString();
yes.setOnClickListener(new OnClickListener() {
public void onClick(View arg0) {
dbhelper.UpdateMasterDesc(str);
loadList(); // see here.
}
});
This is the way I am updating my ListView. I think this is not a good way. If yes means please suggest me how can I update my ListView Whenever I update the database.
Thank You.
notifyDataSetchanged() is the answer as proposed by Raghunandan.
But before calling it, you need to update your object data which has been included in your list of catDesc.
Judging from your code I believe what
dbhelper.UpdateMasterDesc(str);
does is adding a new category? If yes, do a
catDesc.add(new Data(whatever you need to declare it with str))
before calling notifyDataSetChanged().
Hi I am developing small android application in which i using list fragment. I this application what i want to do is fetch data from database and display it with SimpleCursorAdapter and after displaying data in list view I wanted to insert one dummy row at zero position of list which is not from database. My code structure looks like this
public class MyCards extends SherlockListFragment implements
LoaderManager.LoaderCallbacks<Cursor> {
private SimpleCursorAdapter adapter = null;
.
.
.
.
.
private void displayCards()
{
adapter = new SimpleCursorAdapter(this.getActivity(),R.layout.coupon, null, from, to, 0);
setListAdapter(adapter);
// now after this i want to display one dummy row at zero position
}
}
How to do this. Need Help ...
Thank you.
You can achieve like, while filling your array from database, add one dummy data at zero position and then add your actual data from database, and set the array to listivew.
Try this code,
getListView().setSelection(location);
Location is the postion,where you need to set the cursor
EDIT 1
private Vector<RowData> data;
try {
rd=new RowData(iTmp,demo[0], demo[1], demo[2],demo[3],demo[4]);
}
catch (ParseException e)
{
e.printStackTrace();
}
data.add(rd);
//data.add(tokens[iTmp]);
}
CustomAdapter adapter = new CustomAdapter(this, R.layout.firstlist,R.id.title, data);
EDIT 2
Please check this Links
List View Tutorial
1
List View Tutorial
2
I have a listview in which i am adding some data after fixed interval.but I don't want to set the adapter again as it will refresh the complete list.Is there any method to add item without refreshing the complete list.
Thanks in advance.
You probably want to use the following (in RecycleView not ListView):
notifyItemInserted(0);//NOT notifyDataChanged()
recyclerViewSource.scrollToPosition(0);
//Scroll up, to use this you'll need an instance of the adapter's RecycleView
You can call adapter.notifyDataSetChanged() to just update the list.
Adapter's getView() is called at different times and there is no particular pattern. So your views are updated whenever ListView wants it to be updated.
But as far as I see it, you are looking for adapter.notifyDataSetChanged. The workflow should be something like this.
Set adapter to ListView
Add data to adapter`
Call notifyDataSetChanged() on adapter.
It will at least prevent your list to bounce back to first item on the list.
Hope that helps.
you can use this .notifyDataSetChanged()
However notifyDataSetChanged() only works For an ArrayAdapter,if you use the add, insert, remove, and clear functions on the Adapter.
You can use
adapter.add(<new data item>); // to add data to your adapter
adapter.notifyDatasetChanged(); // to refresh
For eg.
ArrayAdapter<String> adapter;
public void onCreate() {
....
....
ArryList<String> data = new ArrayList<String>();
for(int i=0; i<10; i++) {
data.add("Item " + (i+1));
}
adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, data);
setListAdapter(adapter);
}
Now whenever you have new data to be added to list you can do following
private void appendToList(ArrayList<String> newData) {
for(String data : newData)
adapter.add(data);
adapter.notifyDatasetChanged();
}
I have ArrayAdapter with this items structure:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout ... >
<TextView
android:id="#+id/itemTextView"
... />
</RelativeLayout>
And add this adapter so:
mAdapter = new ArrayAdapter<String>(this, R.layout.item,
R.id.itemTextView, itemsText);
All is fine but I want to update text in adapter's items. I found a solution
mAdapter.notifyDataSetChanged();
but do not understand how to use it. Help please.
upd
My code:
String[] itemsText = {"123", "345", "567"};
ArrayAdapter<String> mAdapter;
onCreate
mAdapter = new ArrayAdapter<String>(this, R.layout.roomitem,
R.id.itemTextView, itemsText);
setListAdapter(mAdapter);
itemsText = {"789", "910", "1011"};
onClick
mAdapter.notifyDataSetChanged();
//it's dont work
I think something like this
public void updatedData(List itemsArrayList) {
mAdapter.clear();
if (itemsArrayList != null){
for (Object object : itemsArrayList) {
mAdapter.insert(object, mAdapter.getCount());
}
}
mAdapter.notifyDataSetChanged();
}
Your problem is a typical Java error with pointers.
In a first step you are creating an array and passing this array to the adapter.
In the second step you are creating a new array (so new pointer is created) with new information but the adapter is still pointing to the original array.
// init itemsText var and pass to the adapter
String[] itemsText = {"123", "345", "567"};
mAdapter = new ArrayAdapter<String>(..., itemsText);
//ERROR HERE: itemsText variable will point to a new array instance
itemsText = {"789", "910", "1011"};
So, you can do two things, one, update the array contents instead of creating a new one:
//This will work for your example
items[0]="123";
items[1]="345";
items[2]="567";
... or what I would do, use a List, something like:
List<String> items= new ArrayList<String>(3);
boundedDevices.add("123");
boundedDevices.add("456");
boundedDevices.add("789");
And in the update:
boundedDevices.set("789");
boundedDevices.set("910");
boundedDevices.set("1011");
To add more information, in a real application normally you update the contents of the list adapter with information from a service or content provider, so normally to update the items you would do something like:
//clear the actual results
items.clear()
//add the results coming from a service
items.addAll(serviceResults);
With this you will clear the old results and load the new ones (think that the new results should have a different number of items).
And off course after update the data the call to notifyDataSetChanged();
If you have any doubt don't hesitate to comment.
Assuming itemTexts as String array or String ArrayList,where you are adding new items into itemsTextat that time after that you can call
mAdapter.notifyDataSetChanged();
If you did not get answer then please put some code.
I did something like this. And it works correctly.
Add method to the Adapter class:
public void updateList(ArrayList<ITEM> itemList){
this.itemList.clear();
this.adapterList = new ArrayList<ITEM>();
this.adapterList .addAll(itemList);
notifyDataSetChanged();
}
Call the method in the class you use the adapter:
itemList.add(item);
adapter.updateList(itemList);