Develop Reference

NullPointerException for OnClicklistener for ImageView [duplicate]

Can anyone help me to find out what can be the issue with this program.
In the onCreate() method the findViewById() returns null for all ids and this causes a null pointer exception later. I can not figure out why the findViewById() can not find the view. Any suggestions?
This is the main code:
public class MainActivity extends Activity {
ViewPager pager;
MyPagerAdapter adapter;
LinearLayout layout1, layout2, layout3;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
layout1 = (LinearLayout) findViewById(R.id.first_View);
layout2 = (LinearLayout) findViewById(R.id.second_View);
layout3 = (LinearLayout) findViewById(R.id.third_View);
adapter = new MyPagerAdapter();
pager = (ViewPager) findViewById(R.id.main_pager);
pager.setAdapter(adapter);
}
private class MyPagerAdapter extends PagerAdapter
{
#Override
public int getCount() {
return 3;
}
#Override
public Object instantiateItem(ViewGroup collection, int position) {
LinearLayout l = null;
if (position == 0 )
{
l = layout1;
}
if (position == 1)
{
l = layout2;
}
if (position == 2)
{
l = layout3;
}
collection.addView(l, position);
return l;
}
#Override
public boolean isViewFromObject(View view, Object object) {
return (view==object);
}
#Override
public void destroyItem(ViewGroup collection, int position, Object view) {
collection.removeView((View) view);
}
}
}
And the related XML files:
activity_main layout:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#a4c639">
<android.support.v4.view.ViewPager
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/main_pager"/>
</LinearLayout>
activity_first layout:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/first_View">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/hello_world" />
<Button
android:id="#+id/button1"
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Button" />
</LinearLayout>
activity_second layout:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/second_View">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/hello_world" />
</LinearLayout>
And the activity_third layout:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/third_View">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/hello_world" />
</LinearLayout>

findViewById() returns a View if it exists in the layout you provided in setContentView(), otherwise it returns null and that's what happening to you. Note that if you don't setContentView(), and don't have a valid view to findViewById() on, findViewById() will always return null until you call setContentView().
This also means variables in the top-level trigger an NPE, because they're called before onCreate(), and by extension, before setContentView(). See also the activity lifecycle
Example if you setContentView(R.layout.activity_first); and then call findViewById(R.id.first_View); it will return a View which is your layout.
But if you call findViewById(R.id.second_View); before setContentView(), it will return null since there is not a view in your activity_first.xml layout called #+id/second_View.

Emphasis added
For those cases within an Activity class.
Activity.findViewById(int id)
Finds a view that was identified by the id attribute from the XML that was processed in onCreate(Bundle).
Otherwise, such as an Fragment, Adapter, a View from a LayoutInflater, etc.
View.findViewById(int id)
Look for a child view with the given id. If this view has the given id, return this view.
Either case,
Returns
The view if found or null otherwise.
Now, re-check your XML files. Make sure you put the right value into setContentView or inflater.inflate.
In the case of an Activity, call findViewById after setContentView.
Then, make sure there is a View you are looking for with android:id="#+id/..." in that layout. Make sure the + is at #+id, which will add the resource to the R.id values to ensure you can find it from Java.

The views you're trying to get are not defined in your activity_main layout. You need to programmatically inflate the views you're trying to add to the pager.-
#Override
public Object instantiateItem(ViewGroup collection, int position) {
LinearLayout l = null;
if (position == 0) {
l = (LinearLayout) View.inflate(this, R.layout.activity_first, null);
}
if (position == 1) {
l = (LinearLayout) View.inflate(this, R.layout.activity_second, null);
}
if (position == 2) {
l = (LinearLayout) View.inflate(this, R.layout.activity_third, null);
}
collection.addView(l, position);
return l;
}

Sometimes you need clean your project in Eclipse (Project - Clean..).

add those views to the pager adapter before accessing them.
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
adapter = new MyPagerAdapter();
pager = (ViewPager) findViewById(R.id.main_pager);
pager.setAdapter(adapter);
layout1 = (LinearLayout) findViewById(R.id.first_View);
layout2 = (LinearLayout) findViewById(R.id.second_View);
layout3 = (LinearLayout) findViewById(R.id.third_View);
}
in the pager adapter:
public Object instantiateItem(View collection, int position) {
if(position == 0){
View layout = inflater.inflate(R.layout.activity_first, null);
((ViewPager) collection).addView(layout);
return layout;
}
... and so forth.
}
from here you can access them via findViewById.

In my case, it was a stupid mistake on my part. I had written code in the OnCreate method but it was above the setContentView line of code. Once I moved my code below this line the application started working fine.
setContentView(R.layout.activity_main);

What #Warlock said above is right , you should initial LinearLayout layout1, layout2, layout3 by the right way:
LinearLayout layout1 = (LinearLayout) View.inflate(this, R.layout.first_View, null);
LinearLayout layout2 = (LinearLayout) View.inflate(this, R.layout.second_View, null);
LinearLayout layout3 = (LinearLayout) View.inflate(this, R.layout.third, null);
wish my advise help you

I have gotten this error today and it was so simple to clear, that I "facepalmed".
Just try to add the UI element to your layout xml File in your res/layout-port directory!!!

In Android, findViewById(R.id.some_id) works when you are finding view in the layout set.
That is, if you have set a layout say:
setContentView(R.layout.my_layout);
Views can be found only in this layout (my_layout).
In your code layout1, layout2, layout3 all are three different layouts and they are not set to the activity.

The findViewById method must find what is in the layout (which you called in the setContentView)

Use the adaptor, to inflate the layout, and based on the position you can search for the view.
override fun instantiateItem(collection: ViewGroup, position: Int) : ViewGroup {
val inflater = LayoutInflater.from(mContext)
val layout = inflater.inflate(mData[position], collection, false) as ViewGroup
if(position == your_position) {
val nameOfField: TextView = layout.findViewById(R.id.item_id)
}

This problem is also generated when you are having same name of many components in XML file. Even if they are different layout files you should give every element a unique name.
This error occur because you are having a XML element with the same name in another layout file and android studio is trying to access that and showing this error

Accessing views outside of onCreateView() method

I am trying to make a particular nested FrameLayout visible dynamically. However, i am getting NullPointerException when i try to access the view outside of my fragment's onCreateView() method. So here is my implementation.
private View myView;
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View fragmentView = inflater.inflate(R.layout.listView, container, false);
this.myView = fragmentView;
...
return fragmentView;
}
#Override
public void apiCompleted(ApiResult apiResult, HttpRequest httpRequest) {
if(myLocationManager.hasLocation()){
FrameLayout flayout = (FrameLayout) myView.findViewById(R.id.ldrawlayout);
flayout.setVisibility(View.VISIBLE);
}
}
listView.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#color/background_gray"
tools:context=".fragment.MallListFragment"
android:orientation="vertical">
<ListView
android:id="#+id/lv_malls"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
</ListView>
</LinearLayout>
rowlist.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/row_mallx"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#color/white"
android:paddingBottom="7dp">
<FrameLayout
android:id="#+id/ldrawlayout"
>
...
</FrameLayout>
</RelativeLayout>
LOGCAT (onCreateView method is called first)
01-15 18:40:16.905 7633-7633/? V/onCreateView METHOD CALLED﹕ onCreateView
01-15 18:40:17.280 7633-7633/? V/APICOMPLETED METHOD CALLED﹕ apiCompleted

Ok, I see the problem. You want to access the row-layout, but your listview has multiple versions of this layout, that mean you can not access the row layout from the activity, you have to do it in your listadapter or you give your single rows in the listadapter an unique id such as row.setId(row.getId + positionOfRow)

LayoutInflater Inflater = (LayoutInflater) getActivity().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View view = Inflater.inflate(R.layout.row_mallx, null);
FrameLayout flayout = (FrameLayout) view .findViewById(R.id.ldrawlayout);
flayout.setVisibility(View.VISIBLE);
try this code in on apiCompleted

Are your sure that the onCreateView() method is called before the apiCompleted() method.
If yes, you should be able to access the view any where in your code as long as you hold the reference to it.
You can add some logs to see the order that the functions get called

Android "The specified child already has a parent." for Fragments onCreateView()?

I'm using SherlockFragments in my Android application using the compatibility package. Getting this error for fragments. FATAL EXCEPTION: main
java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first. I am adding these fragments as tabs in actionbar sherlock. After run the app successfully when i am switching tabs first time it's working fine, in second time it's giving the above error in onCreateView()..
this is the code in onCreate()
private static final String AD_UNIT_STANDARD_BANNER = "/6253334/dfp_example_ad/banner";
private DfpAdView adView;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
adView = new DfpAdView(getActivity(), AdSize.BANNER, AD_UNIT_STANDARD_BANNER);
adView.setAdListener(this);
}
this is the code i am using in fragment onCreateView().
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_chats, container, false);
listview = (ListView) view.findViewById(android.R.id.list);
RelativeLayout layout = (RelativeLayout) view.findViewById(R.id.chats_inner_layout);
adView.setId(111);
adView.loadAd(new AdRequest());
RelativeLayout.LayoutParams add_lp = new RelativeLayout.LayoutParams(
RelativeLayout.LayoutParams.MATCH_PARENT, RelativeLayout.LayoutParams.WRAP_CONTENT);
add_lp.addRule(RelativeLayout.BELOW, adView.getId());
listview.setLayoutParams(add_lp);
//**** this is the line causing for error****/////
layout.addView(adView);
return view;
}
this is the xml code for above fragment
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/chats_main_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#color/app_lite_theme"
android:orientation="vertical" >
<RelativeLayout
android:id="#+id/chats_inner_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<ListView
android:id="#android:id/list"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_marginLeft="8dp"
android:layout_marginRight="8dp"
android:scrollbars="none" />
</RelativeLayout>
</RelativeLayout>
this same code i am using for fragments that is working fine without any problems. i am facing problem with fragments only. What is the problem here ? anybody tell
me solution for this.

I think somethings wrong in this part
listview.setLayoutParams(add_lp);
it should be
addView.setLayoutParams(add_lp);

Add static header to listFragment in onCreateView

How can I add a simple static header to my listview inside a listFragment? I want to create the header from an xml def and add it through inflation.
My onCreateView:
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View detailList = inflater.inflate(R.layout.detail_fragment, container, false);
View detailListHeader = inflater.inflate(R.layout.daily_sales_header, null, false);
container.addView(detailListHeader, 0);
return detailList;
}
This creates the header, but it is not above the listview, rather the listview appears underneath the header, ie the header is overlaying the listview.
Any hints on the correct implementation?

Putting hackbod's description into code for you since his answer created more questions before the answers came. Sometimes I just want the fish. I don't always need to know how the net is made...
To start with, create a layout that looks like this:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/myListViewWithHeader"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/header"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="6dp"
android:textStyle="bold"
android:textSize="20sp" />
<ListView
android:id="#android:id/list"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:drawSelectorOnTop="false" />
<TextView
android:id="#android:id/empty"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</LinearLayout>
Then, in your onCreateView method you do this:
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.myListViewWithHeader, null);
return view;
}
The header can now be populated by doing this:
// get the header view
TextView headerView = (TextView) getView().findViewById(R.id.header);
headerView.setText("Header text goes here");
Notice that my header is a TextView, but it can be replaced with another view if you like. In that case you will need to do a getView().findViewById(R.id.xxxxx) for each view inside the header you want to work with

You should NEVER EVER be adding views directly to the container in onCreateView(). Please read the documentation: http://developer.android.com/reference/android/app/Fragment.html#onCreateView(android.view.LayoutInflater, android.view.ViewGroup, android.os.Bundle)
Also see the various sample code in the Fragment documentation, as well as the API demos: http://developer.android.com/resources/samples/ApiDemos/src/com/example/android/apis/app/index.html
There is nothing special about using a Fragment here. Just build a view hierarchy containing a ListView like you normally would in an Activity or elsewhere. You always need to return one View from onCreateView; this is the root of your hierarchy.
For example you could make the ListView and then use this to add a header to it: http://developer.android.com/reference/android/widget/ListView.html#addHeaderView(android.view.View)

Android - Dynamically Add Views into View

I have a layout for a view -
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:padding="0px"
android:orientation="vertical">
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:id="#+id/items_header"
style="#style/Home.ListHeader" />
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:id="#+id/items_none"
android:visibility="gone"
style="#style/TextBlock"
android:paddingLeft="6px" />
<ListView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:id="#+id/items_list" />
</LinearLayout>
What I want to do, is in my main activity with a layout like this
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:padding="0px"
android:id="#+id/item_wrapper">
</LinearLayout>
I want to loop through my data model and inject multiple views consisting of the first layout into the main layout. I know I can do this by building the controls completely within the code, but I was wondering if there was a way to dynamically build the views so that I can continue using a layout instead of putting everything in code.

Use the LayoutInflater to create a view based on your layout template, and then inject it into the view where you need it.
LayoutInflater vi = (LayoutInflater) getApplicationContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View v = vi.inflate(R.layout.your_layout, null);
// fill in any details dynamically here
TextView textView = (TextView) v.findViewById(R.id.a_text_view);
textView.setText("your text");
// insert into main view
ViewGroup insertPoint = (ViewGroup) findViewById(R.id.insert_point);
insertPoint.addView(v, 0, new ViewGroup.LayoutParams(ViewGroup.LayoutParams.FILL_PARENT, ViewGroup.LayoutParams.FILL_PARENT));
You may have to adjust the index where you want to insert the view.
Additionally, set the LayoutParams according to how you would like it to fit in the parent view. e.g. with FILL_PARENT, or MATCH_PARENT, etc.

See the LayoutInflater class.
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
ViewGroup parent = (ViewGroup)findViewById(R.id.where_you_want_to_insert);
inflater.inflate(R.layout.the_child_view, parent);

It looks like what you really want a ListView with a custom adapter to inflate the specified layout. Using an ArrayAdapter and the method notifyDataSetChanged() you have full control of the Views generation and rendering.
Take a look at these tutorials
http://www.softwarepassion.com/android-series-custom-listview-items-and-adapters/
http://developerlife.com/tutorials/?p=327
http://www.androidguys.com/2008/07/14/fancy-listviews-part-one/

To make #Mark Fisher's answer more clear, the inserted view being inflated should be a xml file under layout folder but without a layout (ViewGroup) like LinearLayout etc. inside. My example:
res/layout/my_view.xml
<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/i_am_id"
android:text="my name"
android:textSize="17sp"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1"/>
Then, the insertion point should be a layout like LinearLayout:
res/layout/activity_main.xml
<?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/aaa"
android:layout_width="match_parent"
android:layout_height="match_parent">
<LinearLayout
android:id="#+id/insert_point"
android:layout_width="match_parent"
android:layout_height="match_parent">
</LinearLayout>
</RelativeLayout>
Then the code should be
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_shopping_cart);
LayoutInflater inflater = getLayoutInflater();
View view = inflater.inflate(R.layout.my_view, null);
ViewGroup main = (ViewGroup) findViewById(R.id.insert_point);
main.addView(view, 0);
}
The reason I post this very similar answer is that when I tried to implement Mark's solution, I got stuck on what xml file should I use for insert_point and the child view. I used layout in the child view firstly and it was totally not working, which took me several hours to figure out. So hope my exploration can save others' time.

// Parent layout
LinearLayout parentLayout = (LinearLayout)findViewById(R.id.layout);
// Layout inflater
LayoutInflater layoutInflater = getLayoutInflater();
View view;
for (int i = 1; i < 101; i++){
// Add the text layout to the parent layout
view = layoutInflater.inflate(R.layout.text_layout, parentLayout, false);
// In order to get the view we have to use the new view with text_layout in it
TextView textView = (TextView)view.findViewById(R.id.text);
textView.setText("Row " + i);
// Add the text view to the parent layout
parentLayout.addView(textView);
}