I am trying to populate my Listview using the data from another fragment.
I am able to get the data from the other fragment, but when I try to make my listview object, it is returning null.
As a result, the app is crashing.
I am getting data from the user from one fragment and then calling a method from another fragment to pass the data. I am making my listview object and array adapter in the poplist() method of the second method. However, the app is crashing due to null pointer exception.
Please help.
public class WishListFragment extends Fragment {
ArrayList<String> wishListTitles = new ArrayList<String>();
View rootView;
ListView wishListView;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
Context context = getActivity();
rootView = inflater.inflate(R.layout.fragment_wish_list, container, false);
return rootView;
}
// Another fragment gets the data from user as strings and calls this method
public void popList(String str1, String str2, String str3, Context context)
{
// LibModel is a pojo, I am using its constructor to set the values.
LibModel lm = new LibModel(str1,str2,str3);
Log.w("Title:",lm.getTitle());
Log.w("Author:",lm.getAuthor());
Log.w("Language:",lm.getLang());
wishListTitles.add(lm.getTitle());
// I get this on the log, so the ArrayList is made correctly
Log.w("ArrayList:",wishListTitles.get(0));
// The listView gives Null Pointer exception and crashes the app
wishListView = (ListView) rootView.findViewById(R.id.wl_lv);
ArrayAdapter<String> wishListAdapter = new ArrayAdapter<String>(context,
android.R.layout.simple_list_item_1,wishListTitles);
wishListView.setAdapter(wishListAdapter);
}
}
I have tried the following, but it does not work
Used getView method instead of rootView while making the Listview.
Tried to make the listview inside the onCreateView() method but then the listview object is null, I get null pointer.
I am unable to find a way to put the set the adapter for the listview as it is returning Null.
I would recommend having interface callback in the fragment with the data. Also keep a reference of the list view in the activity containing the fragment.
Upon callback, the interface function will be executed and you can update list view from there.
I have an Activity which holds a ViewPager with 2 Fragments. One fragment is for adding items to ListView and another fragment is holding the ListView.
I've been trying for almost 3 days now without any positive results. How do I update the other fragment's ListView from the first fragment?
I'm trying to call the method that updates ListView from the Activity that holds ViewPager but it doesn't work.
Calling the method from ViewPager activity :
#Override
public void onPageSelected(int position) {
library.populateListView(getApplicationContext());
aBar.setSelectedNavigationItem(position);
}
This is the populateListView method:
public void populateListView(Context context){
CustomListViewAdapter customAdapter = new CustomListViewAdapter(getDatabaseArrayList(context), getActivity());
if (lView != null)
{
lView.setAdapter(customAdapter);
}
customAdapter.notifyDataSetChanged();
}
However this doesn't work because the lView variable (ListView) is null because the fragment isn't shown at the moment when this is being called.
I am assuming that function populateListView() is a function of the Fragment containing the ListView. You are calling populateListView() on every call to onPageSelected. Should you not check what is the position that is being selected. Anyway the populateListView() method should be a public method of the Fragment containing ListView. And You Can Instantiate The Fragment from the Viewpager adapter in the Activity and than call this method. In That way the listView should not be null.
#Override
public void onPageSelected(int position) {
ListViewFragment frag=(ListViewFragment)adapter.instantiateItem(viewPager, 1);
//here adapter is the ViewPager Adapter and you must supply the viewpager that contains
//the fragments and also the position of the fragment to instantiate.
//For example 0 or 1 etc.
frag.populateListView(getApplicationContext());
aBar.setSelectedNavigationItem(position);
}
Understand Fragments
Please see this link. I have gone in great detail explaining the concept of fragments.
Pay particular attention to the definition of rootview:
public void onActivityCreared(Bundle savedInstanceState){
super.onActivityCreated(savedInstanceState);
// Do stuff on creation. This is usually where you add the bulk of your code. Like clickListners
// You can define this object as any element in any of your xml's
View rootview = inflater.inflate(R.layout.xml_the_fragment_uses container,false);
rootview.findViewById(R.id.your_id).setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
//Do something
}
});
}
In the above case I defined a button for an on click listener, but you can just as easily define a ListView along with its appropriate methods.
Alternate Solution
A second method could be using getView or getActivity (check the communicating with activity section).
For example:
ListView listView = (ListView) getView().findViewById(R.id.your_listView_id);
OR (more likely solution for your problem)
View listView = getActivity().findViewById(R.id.list);
Please read this post for additional information.
Good Luck.
To do this safely, you have to keep your listview data in a higher level Parent-Activity not the fragments. Make your MainActivityclass singleton class by making the constructor private and create a getInstance method that return the only initialized instance of your `MainActivity.
This will allow you to keep your data instance safe from being re-initialized or lost. Then, in onResume of your fragment re-set the data (get it from the MainActivity) to your listview adapter and call notifyDataSetChanged() method from the adapter instance.
This will do the trick.
I have got a custom list view adapter and an image button in the adapter class. When i click on the image button, the listener should reload the list view. I need to reload the list view within getview() of adapter class. So I need to know other options than using notifyDataSetChanged() in my listActivity class.
Thanks
You want to refresh a cell inside the listview or do you want to refresh the whole listview, if a single row is loaded inside getView() ?
Check this out:
Android ListView Refresh Single Row
Create a static handler inside the activity which calls a method which reloads the listview and send a message to this handler from the adapter whenever required.
handler = new Handler() {
public void handleMessage(Message paramAnonymousMessage) {
switch (paramAnonymousMessage.what) {
case 1:
populateList();
break;
}
}
};
public void populateBill() {
MyBasketAdapter adapter = new MyBasketAdapter(this, basketList);
listView = (ListView) findViewById(android.R.id.list);
listView.setAdapter(adapter);
}
Inside the adapter class. for example,
button.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
Message msg = Message.obtain();
msg.what = 1;
MyActivity.handler.sendMessage(msg);
}
});
That is very Simple just write a method in your adapter class and call it get view when you deleting or adding anything in your list which you are binding to your adapter.and use notifyDataSetChanged after change in list
public void updateResults(ArrayList<CustomList> results) {
// assign the new result list to your existing list it will work
notifyDataSetChanged();
}
How to refresh an Android ListView after adding/deleting dynamic data?
Call notifyDataSetChanged() on your Adapter object once you've modified the data in that adapter.
Some additional specifics on how/when to call notifyDataSetChanged() can be viewed in this Google I/O video.
Also you can use this:
myListView.invalidateViews();
Please ignore all the invalidate(), invalidateViews(), requestLayout(), ... answers to this question.
The right thing to do (and luckily also marked as right answer) is to call notifyDataSetChanged() on your Adapter.
Troubleshooting
If calling notifyDataSetChanged() doesn't work all the layout methods won't help either. Believe me the ListView was properly updated. If you fail to find the difference you need to check where the data in your adapter comes from.
If this is just a collection you're keeping in memory check that you actually deleted from or added the item(s) to the collection before calling the notifyDataSetChanged().
If you're working with a database or service backend you'll have to call the method to retrieve the information again (or manipulate the in memory data) before calling the notifyDataSetChanged().
The thing is this notifyDataSetChanged only works if the dataset has changed. So that is the place to look if you don't find changes coming through. Debug if needed.
ArrayAdapter vs BaseAdapter
I did find that working with an adapter that lets you manage the collection, like a BaseAdapter works better. Some adapters like the ArrayAdapter already manage their own collection making it harder to get to the proper collection for updates. It's really just an needless extra layer of difficulty in most cases.
UI Thread
It is true that this has to be called from the UI thread. Other answers have examples on how to achieve this. However this is only required if you're working on this information from outside the UI thread. That is from a service or a non UI thread. In simple cases you'll be updating your data from a button click or another activity/fragment. So still within the UI thread. No need to always pop that runOnUiTrhead in.
Quick Example Project
Can be found at https://github.com/hanscappelle/so-2250770.git. Just clone and open the project in Android Studio (gradle). This project has a MainAcitivity building a ListView with all random data. This list can be refreshed using the action menu.
The adapter implementation I created for this example ModelObject exposes the data collection
public class MyListAdapter extends BaseAdapter {
/**
* this is our own collection of data, can be anything we
* want it to be as long as we get the abstract methods
* implemented using this data and work on this data
* (see getter) you should be fine
*/
private List<ModelObject> mData;
/**
* our ctor for this adapter, we'll accept all the things
* we need here
*
* #param mData
*/
public MyListAdapter(final Context context, final List<ModelObject> mData) {
this.mData = mData;
this.mContext = context;
}
public List<ModelObject> getData() {
return mData;
}
// implement all abstract methods here
}
Code from the MainActivity
public class MainActivity extends Activity {
private MyListAdapter mAdapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ListView list = (ListView) findViewById(R.id.list);
// create some dummy data here
List<ModelObject> objects = getRandomData();
// and put it into an adapter for the list
mAdapter = new MyListAdapter(this, objects);
list.setAdapter(mAdapter);
// mAdapter is available in the helper methods below and the
// data will be updated based on action menu interactions
// you could also keep the reference to the android ListView
// object instead and use the {#link ListView#getAdapter()}
// method instead. However you would have to cast that adapter
// to your own instance every time
}
/**
* helper to show what happens when all data is new
*/
private void reloadAllData(){
// get new modified random data
List<ModelObject> objects = getRandomData();
// update data in our adapter
mAdapter.getData().clear();
mAdapter.getData().addAll(objects);
// fire the event
mAdapter.notifyDataSetChanged();
}
/**
* helper to show how only changing properties of data
* elements also works
*/
private void scrambleChecked(){
Random random = new Random();
// update data in our adapter, iterate all objects and
// resetting the checked option
for( ModelObject mo : mAdapter.getData()) {
mo.setChecked(random.nextBoolean());
}
// fire the event
mAdapter.notifyDataSetChanged();
}
}
More Information
Another nice post about the power of listViews is found here: http://www.vogella.com/articles/AndroidListView/article.html
Call runnable whenever you want:
runOnUiThread(run);
OnCreate(), you set your runnable thread:
run = new Runnable() {
public void run() {
//reload content
arraylist.clear();
arraylist.addAll(db.readAll());
adapter.notifyDataSetChanged();
listview.invalidateViews();
listview.refreshDrawableState();
}
};
i got some problems with dynamic refresh of my listview.
Call notifyDataSetChanged() on your Adapter.
Some additional specifics on how/when to call notifyDataSetChanged() can be viewed in this Google I/O video.
notifyDataSetChanged() did not work properly in my case[ I called the notifyDataSetChanged from another class]. Just in the case i edited the ListView in the running Activity (Thread). That video thanks to Christopher gave the final hint.
In my second class i used
Runnable run = new Runnable(){
public void run(){
contactsActivity.update();
}
};
contactsActivity.runOnUiThread(run);
to acces the update() from my Activity. This update includes
myAdapter.notifyDataSetChanged();
to tell the Adapter to refresh the view.
Worked fine as far as I can say.
If you are using SimpleCursorAdapter try calling requery() on the Cursor object.
if you are not still satisfied with ListView Refreshment, you can look at this snippet,this is for loading the listView from DB, Actually what you have to do is simply reload the ListView,after you perform any CRUD Operation
Its not a best way to code, but it will refresh the ListView as you wish..
It works for Me....if u find better solution,please Share...
.......
......
do your CRUD Operations..
......
.....
DBAdapter.open();
DBAdapter.insert_into_SingleList();
// Bring that DB_results and add it to list as its contents....
ls2.setAdapter(new ArrayAdapter(DynTABSample.this,
android.R.layout.simple_list_item_1, DBAdapter.DB_ListView));
DBAdapter.close();
The solutions proposed by people in this post works or not mainly depending on the Android version of your device. For Example to use the AddAll method you have to put android:minSdkVersion="10" in your android device.
To solve this questions for all devices I have created my on own method in my adapter and use inside the add and remove method inherits from ArrayAdapter that update you data without problems.
My Code: Using my own data class RaceResult, you use your own data model.
ResultGpRowAdapter.java
public class ResultGpRowAdapter extends ArrayAdapter<RaceResult> {
Context context;
int resource;
List<RaceResult> data=null;
public ResultGpRowAdapter(Context context, int resource, List<RaceResult> objects) {
super(context, resource, objects);
this.context = context;
this.resource = resource;
this.data = objects;
}
#Override
public View getView(int position, View convertView, ViewGroup parent) {
........
}
//my own method to populate data
public void myAddAll(List<RaceResult> items) {
for (RaceResult item:items){
super.add(item);
}
}
ResultsGp.java
public class ResultsGp extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
...........
...........
ListView list = (ListView)findViewById(R.id.resultsGpList);
ResultGpRowAdapter adapter = new ResultGpRowAdapter(this, R.layout.activity_result_gp_row, new ArrayList<RaceResult>()); //Empty data
list.setAdapter(adapter);
....
....
....
//LOAD a ArrayList<RaceResult> with data
ArrayList<RaceResult> data = new ArrayList<RaceResult>();
data.add(new RaceResult(....));
data.add(new RaceResult(....));
.......
adapter.myAddAll(data); //Your list will be udpdated!!!
For me after changing information in sql database nothing could refresh list view( to be specific expandable list view) so if notifyDataSetChanged() doesn't help, you can try to clear your list first and add it again after that call notifyDataSetChanged(). For example
private List<List<SomeNewArray>> arrayList;
List<SomeNewArray> array1= getArrayList(...);
List<SomeNewArray> array2= getArrayList(...);
arrayList.clear();
arrayList.add(array1);
arrayList.add(array2);
notifyDataSetChanged();
Hope it makes sense for you.
If you want to maintain your scroll position when you refresh, and you can do this:
if (mEventListView.getAdapter() == null) {
EventLogAdapter eventLogAdapter = new EventLogAdapter(mContext, events);
mEventListView.setAdapter(eventLogAdapter);
} else {
((EventLogAdapter)mEventListView.getAdapter()).refill(events);
}
public void refill(List<EventLog> events) {
mEvents.clear();
mEvents.addAll(events);
notifyDataSetChanged();
}
For the detail information, please see Android ListView: Maintain your scroll position when you refresh.
Just use myArrayList.remove(position); inside a listener:
myListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override public void onItemClick(AdapterView<?> parent, android.view.View view, int position, long id) {
myArrayList.remove(position);
myArrayAdapter.notifyDataSetChanged();
}
});
You need to use a single object of that list whoose data you are inflating on ListView. If reference is change then notifyDataSetChanged() does't work .Whenever You are deleting elements from list view also delete them from the list you are using whether it is a ArrayList<> or Something else then Call
notifyDataSetChanged() on object of Your adapter class.
So here see how i managed it in my adapter see below
public class CountryCodeListAdapter extends BaseAdapter implements OnItemClickListener{
private Context context;
private ArrayList<CountryDataObject> dObj;
private ViewHolder holder;
private Typeface itemFont;
private int selectedPosition=-1;
private ArrayList<CountryDataObject> completeList;
public CountryCodeListAdapter(Context context, ArrayList<CountryDataObject> dObj) {
this.context = context;
this.dObj=dObj;
completeList=new ArrayList<CountryDataObject>();
completeList.addAll(dObj);
itemFont=Typeface.createFromAsset(context.getAssets(), "CaviarDreams.ttf");
}
#Override
public int getCount() {
return dObj.size();
}
#Override
public Object getItem(int position) {
return dObj.get(position);
}
#Override
public long getItemId(int position) {
return position;
}
#Override
public View getView(int position, View view, ViewGroup parent) {
if(view==null){
holder = new ViewHolder();
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
view = inflater.inflate(R.layout.states_inflator_layout, null);
holder.textView = ((TextView)view.findViewById(R.id.stateNameInflator));
holder.checkImg=(ImageView)view.findViewById(R.id.checkBoxState);
view.setTag(holder);
}else{
holder = (ViewHolder) view.getTag();
}
holder.textView.setText(dObj.get(position).getCountryName());
holder.textView.setTypeface(itemFont);
if(position==selectedPosition)
{
holder.checkImg.setImageResource(R.drawable.check);
}
else
{
holder.checkImg.setImageResource(R.drawable.uncheck);
}
return view;
}
private class ViewHolder{
private TextView textView;
private ImageView checkImg;
}
public void getFilter(String name) {
dObj.clear();
if(!name.equals("")){
for (CountryDataObject item : completeList) {
if(item.getCountryName().toLowerCase().startsWith(name.toLowerCase(),0)){
dObj.add(item);
}
}
}
else {
dObj.addAll(completeList);
}
selectedPosition=-1;
notifyDataSetChanged();
notifyDataSetInvalidated();
}
#Override
public void onItemClick(AdapterView<?> parent, View view, int position,
long id) {
Registration reg=(Registration)context;
selectedPosition=position;
reg.setSelectedCountryCode("+"+dObj.get(position).getCountryCode());
notifyDataSetChanged();
}
}
Consider you have passed a list to your adapter.
Use:
list.getAdapter().notifyDataSetChanged()
to update your list.
After deleting data from list view, you have to call refreshDrawableState().
Here is the example:
final DatabaseHelper db = new DatabaseHelper (ActivityName.this);
db.open();
db.deleteContact(arg3);
mListView.refreshDrawableState();
db.close();
and deleteContact method in DatabaseHelper class will be somewhat looks like
public boolean deleteContact(long rowId) {
return db.delete(TABLE_NAME, BaseColumns._ID + "=" + rowId, null) > 0;
}
I was not able to get notifyDataSetChanged() to work on updating my SimpleAdapter, so instead I tried first removing all views that were attached to the parent layout using removeAllViews(), then adding the ListView, and that worked, allowing me to update the UI:
LinearLayout results = (LinearLayout)findViewById(R.id.results);
ListView lv = new ListView(this);
ArrayList<HashMap<String,String>> list = new ArrayList<HashMap<String,String>>();
SimpleAdapter adapter = new SimpleAdapter( this, list, R.layout.directory_row,
new String[] { "name", "dept" }, new int[] { R.id.name, R.id.dept } );
for (...) {
HashMap<String, String> map = new HashMap<String, String>();
map.put("name", name);
map.put("dept", dept);
list.add(map);
}
lv.setAdapter(adapter);
results.removeAllViews();
results.addView(lv);
while using SimpleCursorAdapter can call changeCursor(newCursor) on the adapter.
I was the same when, in a fragment, I wanted to populate a ListView (in a single TextView) with the mac address of BLE devices scanned over some time.
What I did was this:
public class Fragment01 extends android.support.v4.app.Fragment implements ...
{
private ListView listView;
private ArrayAdapter<String> arrayAdapter_string;
...
#Override
public void onActivityCreated(Bundle savedInstanceState)
{
...
this.listView= (ListView) super.getActivity().findViewById(R.id.fragment01_listView);
...
this.arrayAdapter_string= new ArrayAdapter<String>(super.getActivity(), R.layout.dispositivo_ble_item, R.id.fragment01_item_textView_titulo);
this.listView.setAdapter(this.arrayAdapter_string);
}
#Override
public void onLeScan(BluetoothDevice device, int rssi, byte[] scanRecord)
{
...
super.getActivity().runOnUiThread(new RefreshListView(device));
}
private class RefreshListView implements Runnable
{
private BluetoothDevice bluetoothDevice;
public RefreshListView(BluetoothDevice bluetoothDevice)
{
this.bluetoothDevice= bluetoothDevice;
}
#Override
public void run()
{
Fragment01.this.arrayAdapter_string.add(new String(bluetoothDevice.toString()));
Fragment01.this.arrayAdapter_string.notifyDataSetChanged();
}
}
Then the ListView began to dynamically populate with the mac address of the devices found.
I think it depends on what you mean by refresh. Do you mean that the GUI display should be refreshed, or do you mean that the child views should be refreshed such that you can programatically call getChildAt(int) and get the view corresponding to what is in the Adapter.
If you want the GUI display refreshed, then call notifyDataSetChanged() on the adapter. The GUI will be refreshed when next redrawn.
If you want to be able to call getChildAt(int) and get a view that reflects what is what is in the adapter, then call to layoutChildren(). This will cause the child view to be reconstructed from the adapter data.
I had an ArrayList which I wanted to display in a listview. ArrayList contained elements from mysql.
I overrided onRefresh method and in that method I used tablelayout.removeAllViews(); and then repeated the process for getting data again from the database.
But before that make sure to clear your ArrayList or whatever data structre or else new data will get appended to the old one..
If you want to update the UI listview from a service, then make the adapter static in your Main activity and do this:
#Override
public void onDestroy() {
if (MainActivity.isInFront == true) {
if (MainActivity.adapter != null) {
MainActivity.adapter.notifyDataSetChanged();
}
MainActivity.listView.setAdapter(MainActivity.adapter);
}
}
If you are going by android guide lines and you are using the ContentProviders to get data from Database and you are displaying it in the ListView using the CursorLoader and CursorAdapters ,then you all changes to the related data will automatically be reflected in the ListView.
Your getContext().getContentResolver().notifyChange(uri, null); on the cursor in the ContentProvider will be enough to reflect the changes .No need for the extra work around.
But when you are not using these all then you need to tell the adapter when the dataset is changing. Also you need to re-populate / reload your dataset (say list) and then you need to call notifyDataSetChanged() on the adapter.
notifyDataSetChanged()wont work if there is no the changes in the datset.
Here is the comment above the method in docs-
/**
* Notifies the attached observers that the underlying data has been changed
* and any View reflecting the data set should refresh itself.
*/
I was only able to get notifyDataSetChanged only by getting new adapter data, then resetting the adapter for the list view, then making the call like so:
expandableAdapter = baseFragmentParent.setupEXLVAdapter();
baseFragmentParent.setAdapter(expandableAdapter);
expandableAdapter.notifyDataSetChanged();
on other option is onWindowFocusChanged method, but sure its sensitive and needs some extra coding for whom is interested
override fun onWindowFocusChanged(hasFocus: Boolean) {
super.onWindowFocusChanged(hasFocus)
// some controls needed
programList = usersDBHelper.readProgram(model.title!!)
notesAdapter = DailyAdapter(this, programList)
notesAdapter.notifyDataSetChanged()
listview_act_daily.adapter = notesAdapter
}
If I talked about my scenario here, non of above answers will not worked because I had activity that show list of db values along with a delete button and when a delete button is pressed, I wanted to delete that item from the list.
The cool thing was, I did not used recycler view but a simple list view and that list view initialized in the adapter class. So, calling the notifyDataSetChanged() will not do anything inside the adapter class and even in the activity class where adapter object is initialized because delete method was in the adapter class.
So, the solution was to remove the object from the adapter in the adapter class getView method(to only delete that specific object but if you want to delete all, call clear()).
To you to get some idea, what was my code look like,
public class WordAdapter extends ArrayAdapter<Word> {
Context context;
public WordAdapter(Activity context, ArrayList<Word> words) {}
//.......
#NonNull
#Override
public View getView(final int position, View convertView, ViewGroup group) {
//.......
ImageButton deleteBt = listItemView.findViewById(R.id.word_delete_bt);
deleteBt.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if (vocabDb.deleteWord(currentWord.id)) {
//.....
} else{
//.....
}
remove(getItem(position)); // <---- here is the trick ---<
//clear() // if you want to clear everything
}
});
//....
Note: here remove() and getItem() methods are inherit from the Adapter class.
remove() - to remove the specific item that is clicked
getItem(position) - is to get the item(here, thats my Word object
that I have added to the list) from the clicked position.
This is how I set the adapter to the listview in the activity class,
ArrayList<Word> wordList = new ArrayList();
WordAdapter adapter = new WordAdapter(this, wordList);
ListView list_view = (ListView) findViewById(R.id.activity_view_words);
list_view.setAdapter(adapter);
After adding/deleting dynamic data in your "dataArray" do:
if you use an ArrayAdapter
adapter.notifyDataSetChanged();
if you use a customAdapter that extends ArrayAdapter
adapter.clear();
adapter.addAll(dataArray);
adapter.notifyDataSetChanged();
if you use a customAdapter that extends BaseAdapter
adapter.clear();
adapter.getData().addAll(dataArray);
adapter.getData().notifyDataSetChanged();
The easiest is to just make a new Adaper and drop the old one:
myListView.setAdapter(new MyListAdapter(...));