Develop Reference

Setting an Adapter to the ListView Android Studio

I'm trying to add some items in a ListView. When I swith the Layout (startActivity), I call the class Listing.
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_listing);
ListView lv = (ListView) findViewById(R.id.listViewLIST);
String[] items = {"Item1", "Item2", "Item3", "Item4"};
ArrayList<String> arrayList = new ArrayList<>(Arrays.asList(items));
ArrayAdapter<String> adapter = new ArrayAdapter<>(this, R.layout.activity_listing, R.id.listViewLIST, arrayList);
lv.setAdapter(adapter);
}
I read some tutorials an followed every step but the app stops working always in the last line of code
lv.setAdapter(adapter);
What am I missing?
Edit 27.12.2015
The activity_listing.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools" android:layout_height="match_parent" android:fitsSystemWindows="true"
tools:context="cigarkings.cigarking.Listing">
<ListView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/listViewLIST"
android:layout_alignParentTop="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
android:layout_marginTop="51dp" />
<SearchView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/searchView"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignRight="#+id/listView"
android:layout_alignEnd="#+id/listView" />
<include layout="#layout/content_listing" />
</android.support.design.widget.CoordinatorLayout>

Assuming missing statement android:layout_width="match_parent" for your Coordinator Layout as a typographical error,the major error is in setting up array adapter.
In the statement : ArrayAdapter<String> adapter = new ArrayAdapter<>(this, R.layout.activity_listing, R.id.listViewLIST, arrayList); the constructor parameters (2nd parameter:R.layout.activity_listing and 3rd parameter:R.id.listViewLIST) are incorrect.Array Adapter takes resource id of a textview as 3rd argument and not of a listview, and the layout resource id of the layout containing the textview is passed as 2nd argument.
So, one solution for this is to create a separate xml layout containing a textview and passing the layout resource id as 2nd argument and textview id as 3rd argument to the constructor of Array Adapter

First of all activity listing should not be in this pattern.
If you are at beginning stage then First try this Tutorial...
The best explanation ever for beginners.
Then you have to implement custom listView using BaseAdaptor class and custom XML.

Android Views within Layouts

Ok so I'm running into problems creating an app (force closing) and I think it has to do with the way I implemented the layout. So a few questions: First, I have a relative layout that includes a text input with a button next to it, a list view (still within the relative layout) and another button below that. This is my main xml file:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/RelativeLayout1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
<EditText
android:id="#+id/edit_choice"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="#+id/Button1"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_toLeftOf="#+id/Button1"
android:hint="#string/edit_choice" />
<Button
android:id="#+id/Button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:layout_alignParentTop="true"
android:onClick="addString"
android:text="#string/button_add" />
<Button
android:id="#+id/Button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:layout_marginBottom="22dp"
android:text="#string/button_random" />
<ListView
android:id="#+id/listView1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_above="#+id/Button2"
android:layout_alignParentLeft="true"
android:layout_below="#+id/Button1"
tools:listitem="#android:layout/simple_list_item_1" >
</ListView>
</RelativeLayout>
Before I even changed anything in the .java files when I tried running this, only the text input and the 2 buttons appeared and the theme changed from Holo to Holo light. So I'm wondering if this works, I've only seen examples where the list view matches the parent layout completely.
My second question is how do I handle using the input to add values to the list view, can I do that in the main activity class or can I have another class to handle the list view and still reference the main layout.
This is my Main class:
public class MainActivity extends Activity
{
public ArrayList <String> choices = new ArrayList <String>();
public ListView listView = (ListView) findViewById(R.id.listView1);
public String [] choicesArray;
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ListView listView = (ListView) findViewById(R.id.listView1);
choicesArray = new String [] {"You have not entered a choice yet"};
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, android.R.id.text1, choicesArray);
listView.setAdapter(adapter);
}
#Override
public boolean onCreateOptionsMenu(Menu menu)
{
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
//adds the string to the list
public void addString(View view)
{
choicesArray = (String[]) choices.toArray();
EditText editText = (EditText) findViewById(R.id.edit_choice);
String message = editText.getText().toString();
choices.add(message);
}
}
Hopefully this makes sense and thank you for any help.

Problem is you are calling this line
public ListView listView = (ListView) findViewById(R.id.listView1);
before setting content view by setContentView() method in onCreate() so you are getting NullPointerException. Do not forget that before calling findViewById you have to set content view. So delete above line because you are creating function scope listView in onCreate method and your NullPointerException problem will be solved. And also change first line of addString method like this
choicesArray = choices.toArray(choicesArray);

Define your ArrayAdapter as member for your class (not as variable
in onCreate()).
Set the adapter to your listView in onCreate().
Set the onClickListener for your button.
Add the text from EditText to your adapter when you click on the
button.
Profit!

View is null even after initialization

I have a listview in my code and I want to set adapter on it.
But the issue is, even after initializing the listview, it is still null resulting into nullPointerException. (I checked it by logging and debugging)
I'm not able to access any view from that xml.
What am I missing? Any help appreciated.
xml
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
android:scrollbars="vertical" >
<RelativeLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content" >
<ListView
android:id="#+id/lvToday"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:divider="#FFF"
android:dividerHeight="2dp" />
<ListView
android:id="#+id/lvTomorrow"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#id/lvToday"
android:divider="#FFF"
android:dividerHeight="2dp" />
</RelativeLayout>
</ScrollView>
Activity file
public class DashboardActivity extends Activity {
ListView lvToday, lvTomorrow;
TextView lblCall;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.dashboard);
init();
}
private void init() {
lvToday = (ListView) findViewById(R.id.lvToday);
lvTomorrow = (ListView) findViewById(R.id.lvTomorrow);
TodayAppAdapter adapter = new TodayAppAdapter(DashboardActivity.this,
DashboardActivity.this);
// This line is giving NULL
lvToday.setAdapter(adapter);
TomorrowAppAdapter adapter1 = new TomorrowAppAdapter(
DashboardActivity.this, DashboardActivity.this);
// This line is giving NULL
lvTomorrow.setAdapter(adapter1);
}
}

1) test eclipse menu: Project -> Clean...
2) if you have more than one version for your xml layout (example layout-large, layout-xlarge,...), check if all of them have your view.

You are missing a TextView in your layout

Put a String []
along with name of your Adapter in your
OnDraw()
Method

Display contents from ListView defined in regular Activity Android

I wanted to create a search view like the one Google uses. For this I created the following XML layout, which basically is a search bar and a button in the upper section of the screen and a ListView at the bottom of it.
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/LinearLayoutSearch"
android:layout_height="fill_parent"
android:layout_width="fill_parent"
android:background="#FF394952">
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_alignParentTop="true" >
<EditText android:layout_height="wrap_content" android:id="#+id/searchTextBar" android:layout_width="wrap_content" android:layout_weight="1">
<requestFocus></requestFocus>
</EditText>
<Button android:layout_height="fill_parent" android:layout_width="wrap_content" android:id="#+id/searchButton" android:text="Buscar"></Button>
</LinearLayout>
<ListView
android:id="#+id/searchResultList"
android:layout_height="wrap_content"
android:layout_width="fill_parent"
android:layout_alignParentBottom="true"
android:layout_weight="1.0" />
</LinearLayout>
And this is the code of the textViewResource that the ArrayAdapter demands on its constructor:
<?xml version="1.0" encoding="utf-8"?>
<TextView
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
</TextView>
Now, this is the code of the activity. So far, I just want to display the view with the contents (that's why I'm using a static String array for now).
public class SearchActivity extends Activity{
static final String[] COUNTRIES = new String[] {
"Afghanistan", "Albania", "Algeria"};
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.searchview);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,R.layout.list_item, COUNTRIES);
ListView lv = (ListView)this.findViewById(R.id.searchResultList);
lv.setAdapter(adapter);
lv.setTextFilterEnabled(true);
lv.setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// When clicked, show a toast with the TextView text
Toast.makeText(getApplicationContext(), ((TextView) view).getText(),
Toast.LENGTH_SHORT).show();
}
});
}
}
However, when I run the activity I see the search bar but it doesn't display the ListView.
I've tried changing the extension of SearchActivity to ListActivity, but the program just crashes when I try to start it. I'm also aware of the existence of the Search Interface, but I just want to see this particular method work.
Why it doesn't display the contents of the ListView? Is there a way to fix this?
Thanks in advance

If you are going to use ListActivity you should be aware that ListActivity already has a ListView instance. You need to call its setListAdapter method to set the adapter for its ListView instead of instantiating your own ListView and setting the adapter on it. You can call getListView to get a handle on ListActvity's ListView and then set the click listener on that.

If you want to extend ListActivity then you must have a ListView with id #android:id/list. Change the id of your ListView, that should fix the crash when extending ListActivity.

How to use R to select a ListView when using it with ListActivity

I have this code:
public class MyActivity extends ListActivity implements OnClickListener {
private ArrayList<String> listItems = new ArrayList<String>();
ArrayAdapter<String> adapter;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.setAdapter();
this.bindButtons();
}
private void setAdapter() {
setContentView(R.layout.siteactivity);
adapter=new ArrayAdapter<String>(this,
R.layout.siteitem,
listItems);
setListAdapter(adapter);
}
private void bindButtons() {
findViewById(R.id.buttonPrevious).setOnClickListener(this);
findViewById(R.id.buttonNext).setOnClickListener(this);
}
// ...
}
with this layout:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent" android:id="#+id/siteActivity">
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:id="#+id/navigation">
<Button
android:text="<="
android:textSize="12dp"
android:id="#+id/buttonPrevious"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
</Button>
<Button
android:text="=>"
android:textSize="12dp"
android:id="#+id/buttonNext"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
</Button>
</LinearLayout>
<ListView
android:id="#android:id/list"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/navigation"
android:layout_above="#+id/transport_selection"
/>
</RelativeLayout>
Note the android:id="#android:id/list" of the ListView. If I replace it by android:id="#+id/list", my activity force closes, because my "content must have a ListView whose id attribute is 'android.R.id.list'", but this is the expected behaviour, I think.
Now, I want to add a context menu to the items of the ListView. I tryed registerForContextMenu(findViewById(R.id.list));, but it doesn't work, because of the android:id.
Then, how can I add a context menu?
Regards,

As you are using ListActivity, you can use the following code to get list view in code:
ListView myListView=getListView ();

Use android.R.id.list instead of R.id.list.
(And by the way, the error message you wrote here turns out to have the answer)
Basically, anything defined in XML as #android:whatever is the same as android.R.whatever in the Java code. Anything that you defined in XML, which will look like #whatever, is the same as R.whatever in Java code.
Final edit: If you're using ListActivity, you are required to have a ListView with the id #android:id/list. Thus, unless you want to add another ListView to your activity, you shouldn't need #+id/list (or R.id.list).

You need to create an AlertDialog and call the dialog to show inside the listview's onItemLongClick() event. Click here for an example.