I have a listview that shows the contents of an arraylist. I'm using a simple adaptor to make this possible like so.
public static ArrayList<String> homeScreenContacts = new ArrayList<String>();
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
R.layout.home_screen_contacts_view, NewContact.homeScreenContacts);
The second line is giving me a null pointer exception. I thought about it and I decided it was because the arrayList is empty. So I added the following line between the arraylist declaration and the arrayadaptor declaration...
NewContact.homeScreenContacts.add("A Contact");
This solved the problem and my code worked fine but Now the list view shows "A Contact" and I dont want it to. Is there anyway to get rid of the null pointer exception problem but still have the arraylist empty? Because I want to populate it with user made contacts, not hard-coded, random strings. Thank you.
EDIT: Sorry, The arraylist is located in another class called NewContact, also, I am very beginner Android Programmer I just started.
Simple solution just don't initialize the ListView if there is no element in the ArrayList or the ArrayList is null.
if(NewContact.homeScreenContacts != null && NewContact.homeScreenContacts.size() > 0){
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
R.layout.home_screen_contacts_view, NewContact.homeScreenContacts);
listView.setAdapter(adapter);
}
Also you need to remember that if you you haven't initialize Adapter then dont initialize the ListView and before any operation on list view you should check is it null or not.
As you have said that you want to populate when user add some contact in the application then on add event only you need to populate or update the ListAdapter.
Hope this solution will resolve your problem.
Try this code
public class YourActivity extends Activity
{
private ListView lv;
public void onCreate(Bundle saveInstanceState) {
setContentView(R.layout.your_layout);
lv = (ListView) findViewById(R.id.your_list_view_id);
// Instanciating an array list (you don't need to do this, you already have yours)
ArrayList<String> your_array_list = new ArrayList<String>();
your_array_list.add("foo");
your_array_list.add("bar");
// This is the array adapter, it takes the context of the activity as a first // parameter, the type of list view as a second parameter and your array as a third parameter
ArrayAdapter<String> arrayAdapter =
new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1, your_array_list);
lv.setAdapter(arrayAdapter);
}
}
Works fine for me:
if(arrayList.isEmpty())
{
listView.setAdapter(null);
}
else
{
listAdapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,arrayList);
listView.setAdapter(listAdapter);
}
Related
I'm attempting to get method to handle updates to the ListView when SetWeatherData is called. Nothing ever shows up in my listview below. Any ideas? _rootView points to the right root and ListView comes back not null. m_weatherdata has a couple string elements in it.
Note the initial set of data does not show up either. Just blank.
I'm thinking it should be easier to setup a generic method to update a ListView when the data changes using straight up code.
private ArrayList<String> m_weatherdata;
private void SetWeatherData ( ArrayList<String> _weather)
{
m_weatherdata = _weather;
UpdateWeatherUI();
return;
}
ArrayAdapter<String> m_adapter = null;
private void UpdateWeatherUI()
{
if ( m_adapter == null ) {
m_adapter = new ArrayAdapter<String>(
this.getContext(),
R.layout.list_item_forecast,
R.id.list_item_forecast_textview,
m_weatherdata);
View _rootview = this.getLayoutInflater(null).inflate(R.layout.fragment_main, null, false);
ListView _listview = (ListView) _rootview.findViewById(R.id.listview_forecast);
_listview.setAdapter(m_adapter);
}
else
{
m_adapter.notifyDataSetChanged();
}
}
You are assigning a new ArrayList to your dataset.
m_weatherdata = _weather;
Instead add items to the dataset. Like this
m_weatherdata.addAll(_weather);
private void SetWeatherData ( ArrayList<String> _weather)
{
m_weatherdata.addAll(_weather);//change here
UpdateWeatherUI();
return;
}
When you set an adapter there is an observer attached to the
underlying data. So notifyDatasetChanged() only works if you only
modify the data in it.
If you want to clear all data from your dataset before adding new items to it, use the clear() method of ArrayList
private void SetWeatherData ( ArrayList<String> _weather)
{
m_weatherdata.clear();//change here
m_weatherdata.addAll(_weather);//change here
UpdateWeatherUI();
return;
}
m_weatherdata = _weather; // updates the local variable with new set of data. but adapter doesn't know about the changes made as you have created the instance of the adapter with array list by the following line of code.
m_adapter = new ArrayAdapter<String>(this.getContext(), R.layout.list_item_forecast,R.id.list_item_forecast_textview,m_weatherdata);
In you want to updated the data either call
m_adapter.addAll(newsetofstringtobeadded);
or
Create new adapter
This will update your list.
I am trying to create an array adapter to populate my list view.
Below is the code I have however the Array Adapter gets the error "Cannot resolve constructor".
Can anybody please help me with why this might be happening?
Thanks.
private void populateListView(){
//Create list of items'
String[] myItems = {"Blue", "red", "green", "purple"};
//Build adapter
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, R.layout.deal_items, myItems);
//Configure the list view
ListView list = (ListView) findViewById(R.id.listViewMain);
list.setAdapter(adapter);
}
The first parameter to the ArrayAdapter constructor needs to be a Context. You appear to have implemented this method in a Fragment, which is not a Context. If so, then replace this in the ArrayAdapter constructor with getActivity().
I saw that there were many problems regarding notifyDataSetChanged(). I've looked through many of them and none of the solutions worked for me.
I am using ArrayList to set my list, and after my ArrayList is updated, i ran notifyDataSetChanged(). The new list is added onto the previous one.
lets say first list is a,b and new list is a,b,c. what i get in the end is a,b,a,b,c.
and each time updating this happens again with the new list.
I've tried other such as invalidate(), adapter clear(), refreshDrawableState() etc and nothing worked.
Thank you in advance.
Here is the simplified code, a note that changing MainActivity extends Activity to ListActivity crashes the program even after i change the code in .xml file.
public class MainActivity extends Activity
{
ArrayList<String> names = new ArrayList<String>();
ArrayAdapter arrayAdapter = null;
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ListView lv1 = (ListView) findViewById(R.id.listview);
arrayAdapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1, names);
lv1.setAdapter(arrayAdapter);
}
//code here to edit the ArrayList names.
public void onResume()
{
super.onResume(); // Always call the superclass method first
//the activity need to be updated everytime it resumes.
arrayAdapter.notifyDataSetChanged();
}
}
Seems like you are not properly updating the array list. Please try logging the array list contents after updating.
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);
I have an array of apps(PInfo) and I am wondering how do I add that array to a listview?
ArrayList<PInfo> info = appsGetter.listPackages();
int number = 0;
PInfo appInArray;
while(number < info.size()){
appInArray = info.get(number);
}
This is what I have at the moment, the listPackages() is a method that is getting the names of the apps from the device.
At the moment I am trying to get the information out of the array one by one and add it to the listview like that. Is that how I should do it our should I add the array straight to the listview? And how do you do that?
You can use an ArrayAdapter and initialize it like this:
ArrayAdapter<PInfo> adapter = new ArrayAdapter(context,
android.R.layout.simple_list_item_multiple_choice,
info);
Then you can you use ListView.setAdapter(adapter).
I'm not sure if this is what you're asking though. So please clarify further if this is not what you're asking
Try using an Adapter. For example (using just the String value of an object) you could do the following:
ListView listView = (ListView)findViewById( R.id.myListView );
final ArrayList<String> listItems = new ArrayList<String>();
final ArrayAdapter<String> adapter = new ArrayAdapter<String>( this, android.R.layout.simple_list_item_1, listItems );
listView.setAdapter( adapter );
Just a quick example, but I hope it gives you a starting place. Just make sure if you add values to your data source later (in this case the ArrayList) to call the adapter's "notifyDataSetChanged()" method so that it can be properly reflected in whatever has been bound to the adapter (in this case the ListView).
You need to use an ArrayAdapter. Just search for a ListView and ArrayAdapter sample online. It's quite simple once you see it done.