What is the difference between getView() and getActivity()?
I have used both methods but don't understand the basic difference even methodology of usage are also same in android:
ListView deliverItemList = (ListView) getView().findViewById(R.id.load_item_list);
ListView deliverItemList = (ListView) getActivity().findViewById(R.id.load_item_list);
I have assumed that getView() may produce NullPointerException, share your knowledge with me and which method is recommended?
getActivity() returns the Activity hosting the Fragment, while getView() returns the view you inflated and returned by onCreateView. The latter returns a value != null only after onCreateView returns
From android docs:
getActivity() returns the Activity this fragment is currently
associated with, and getView() returns the root view for the
fragment's layout (the one returned by onCreateView(LayoutInflater,
ViewGroup, Bundle)), if provided.
So, in your case, by the following line of code:
getView().findViewById(R.id.load_item_list);
you are searching for the view in your fragment, but using the following line of code:
getActivity().findViewById(R.id.load_item_list);
you are searching for the view in your activity hosting your fragment.
About your question of which one to use, it depends. If you are trying to inflate fragment, you need to inflate your xml in onCreateView, and using that inflated view you search for your views like this:
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.your_layout, container, false);
ListView lv = (ListView)v.findViewById(R.id.view_id);
}
Related
This code works:
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_detail, container, false);
Intent intent = getActivity().getIntent();
String weather = intent.getStringExtra(Intent.EXTRA_TEXT);
if(weather != null) {
TextView textViewWeather=(TextView)rootView.findViewById(R.id.weatherText);
textViewWeather.setText(weather);
BUT if you replace, in the line
(TextView)rootView.findViewById(R.id.weatherText);
rootView by findView() or getActivity, it returns null so the next line creates a run time fatal error which halts the program.
I don't understand why. I thought that the context is the activity?! I'm confused,and can't find a good answer via android developer,so here I am...
Thanks in advance to whoever helps!!
when you call :
View rootView = inflater.inflate(R.layout.fragment_detail, container, false);
TextView textViewWeather=(TextView)rootView.findViewById(R.id.weatherText);
the rootView now contains the views that are defined in fargment_detail.xml .
and weatherText is one of them.
but when you call getActivity().findViewById() or findViewById() you want to find the weatherText inside xml file of activity and there is no weatherText there so it will retun null
This line gets the element with id weatherText from its rootView. Which is nothing but your fragment xml file
TextView textViewWeather=(TextView)rootView.findViewById(R.id.weatherText);
Now if you are replacing above code with below
TextView textViewWeather=(TextView)getActivity().findViewById(R.id.weatherText);
now the parent Activity in which this fragment is hosted which has TextView and id weatherText will be searched by framework. Which is obvious is not present at all.
If you remove the rootView you are calling it directly on the activity so those two suggestions are equal (and activity is indeed the context).
But the activity doesn't know about the layout yet, you just inflated it from xml but it has not been given to the activity yet, and therefore can't be found. You do that by returning it from the onCreateView call you are in in your example code.
I want to have a fragment for each item in a listview, because I want to separate some logic out. I am using a view holder for each item. If the view doesn't exist, I create a new fragment and add it into the container.
holder.mMyFragment = new MyFragment(mActivity, this);
mActivity.getSupportFragmentManager().beginTransaction().add(R.id.my_container, holder.mMyFragment).commit();
Also for each item, I call holder.mMyFragment.setUi(dataSource, position) to set UI of the fragment based on the data source and position.
The problem I'm having is I initialize the UI elements of fragment in onCreateView method of the fragment class, but it's not called when I add the fragment to the item. So later when I call setUi() which uses some UI elements in fragment it complains a NullPointerException. Does anyone have a suggestion? Thanks!
"THERE IS A SOLUTION" for this.
The issue is, you cannot add fragment directly to the container(FrameLayout) with same "id" in listview as you have done in the above code.
The trick is, create listview(Recyclerview) of "LinearLayout". Then dynamically create FrameLayout in adapter and assign different id's for each. Inflate Fragment to FrameLayout and this FrameLayout to LinearLayout.
#Override
protected void onBindBasicItemView(RecyclerView.ViewHolder holder, int position) {
if (holder instanceof VideoHomeViewHolder) {
VideoHomeViewHolder videoHomeViewHolder = (VideoHomeViewHolder) holder;
FrameLayout frameLayout = new FrameLayout(mContext);
frameLayout.setId(position+1); //since id cannot be zero
FragmentHelper.popBackStackAndReplace(mFragmentManager, frameLayout.getId(),
new ShowLatestVideosFragment(mShowLatestVideosItems.get(position)));
videoHomeViewHolder.linearLayout.addView(frameLayout);
}
}
I want to have a fragment for each item in a listview, because I want to separate some logic out.
You can't use fragment as list item views because the API doesn't allow you - View and Fragment aren't even related so there's no way you can use it like that. Make custom views and use adapter getViewTypeCount and getView to use different list item behavior.
Fragment are managed by Activity's FragmentManager or by other Fragments child FragmentManager; while list item views are managed by ListView & ListAdapter. You can use ListViews in Fragments, but not the other way around.
A simple way.
One problem:You should store add restore fragment state.
holder.mMyFragment = new MyFragment(mActivity, this);
int id = View.generateViewId();
findViewByTag("abc").setId(id);
mActivity.getSupportFragmentManager().beginTransaction().add(id, holder.mMyFragment).commit();
Hi I was facing the same problem and I found the way to do it.
My problem was similar to you:
"I want to have a fragment for each item in a listview, because I want to separate some logic out"
In my app I have to give the option to display custom items in vertical (listView) and horizontal (ViewPager) mode. Additionally I had to deal with 18 custom items and each one with different logic, so the best approach was reusing the fragments that I was using for ViewPager in ListView.
I got it but not in the way you were trying, I mean, I used my fragments like "ViewHolders":
Define fragment's widget like variables of class in each fragment.
Create a custom ArrayAdapter and override: getViewTypeCount(), getItemViewType(int position), getCount(), getItem(int position) getView(int position, View convertView, ViewGroup parent)
In getView I checked what kind of layout I needed before "inflate" the respective XML, create a fragment, assign widget from XML to fragment (with rootView.findViewById) and set "tag" with the new fragment.
What you can see at this point is that fragments in ListView never got attached to Activity but you got what you wanted: logic distributed in several parts and all benefits of ListView (reuse of rows, scroll, etc).
If you need I can post part of my code but you have to deal with "spanglish" ;).
UPDATED
All the problem is because when you create a Fragment to be used with ViewPager, usually all "layout and "setup" code is inside onCreateView method, I mean:
Get the view object you are going to use (View rootView = inflater.inflate(R.layout.fragment_question_horizontal_container, container, false);)
Get the widgets from above layout, define behaviors, fonts, etc: (answer = (EditText)rootView.findViewById(R.id.answer_question_text);)
Until this point there is nothing weird.
If you are going to use a fragment with the behavior described above you have to "emulate" the call to onCreateView, fill the data and attach it to the listView.
Here is the trick: split the code in onCreateView in some methods that doesn't care about who's calling them. An example of my onCreateView:
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_pregunta_horizontal_container, container, false);
addAnswerLayout(rootView, R.layout.fragment_pregunta_texto, getActivity());
setUpComponents(rootView);
//those 2 methods are about my app logic so I'm not going to talk much about them
setUpQuestionState(savedInstanceState);
readSavedAnswer();
return rootView;
}
public void addAnswerLayout(View rootView, int optionId, Context context) {
mContext = context;
RelativeLayout relativeLayout = (RelativeLayout)rootView.findViewById(R.id.pregunta_container);
LayoutInflater inflater = ((Activity)mContext).getLayoutInflater();
View newView = inflater.inflate(optionId, relativeLayout, false);
relativeLayout.addView(newView);
}
public void setUpComponents(View rootView) {
//next line: some heritage that you can ignore
super.setUpComponents(rootView);
respuesta = (EditText)rootView.findViewById(R.id.pregunta_respuesta_texto);
respuesta.setTypeface(UiHelper.getInstance(getActivity()).typeface);
respuesta.setTextColor(mContext.getResources().getColor(R.color.drs_gris));
...
}
Now let's go to the CustomArrayAdapter for list view:
Define your customArrayAdapter something like this: PreguntasVerticalArrayAdapter extends ArrayAdapter<Pregunta> where "Pregunta" is a generic Fragment with the logic from above.
Override getViewTypeCount(), getItemViewType(int position), getCount(), getItem(int position) getView(int position, View convertView, ViewGroup parent).
The getView follow the same behavior: get the object for the given position in params, reuse a "viewholder" and fill the data. Here my getView:
#Override
public View getView(int position, View convertView, ViewGroup parent) {
View rowView = convertView;
Pregunta pregunta = mData.get(position);
if (rowView == null)
rowView = createQuestionUI(pregunta, parent, position);
fillDataInRow((PreguntaUI)rowView.getTag(), pregunta, position);
return rowView;
}
private View createPreguntaUI(Pregunta pregunta, ViewGroup parent, int position) {
View rootView = null;
LayoutInflater inflater = (mPreguntasVerticalFragment.getActivity()).getLayoutInflater();
//you can ignore this part of the code ralted to Bundle.
Bundle args = new Bundle();
args.putLong(PreguntaUI.PREGUNTAUI_ID, pregunta.getIdpregunta());
args.putInt(PreguntaUI.PREGUNTAUI_INDEX, position);
args.putInt(PreguntaUI.PREGUNTAUI_TOTAL_QUESTIONS, getCount());
//internal method of "pregunta" to know what kind of question it is.
String tipo = pregunta.getTipo();
if (tipo.equalsIgnoreCase(PreguntaType.TEXT.toString())) {
rootView = inflater.inflate(R.layout.fragment_pregunta_vertical_container, parent, false);
Pregunta_texto pregunta_texto = new Pregunta_texto();
pregunta_texto.setArguments(args);
//LOOK AT THIS POINT!!!: I'm calling the same methods that I called in onCreateView fragment's method.
pregunta_texto.addAnswerLayout(rootView, R.layout.fragment_pregunta_texto,
mPreguntasVerticalFragment.getActivity());
pregunta_texto.setUpComponents(rootView);
pregunta_texto.setUpQuestionState(null);
pregunta_texto.readSavedAnswer();
//I'm adding the fragment to reuse it when I can
rootView.setTag(pregunta_texto);
}
else if ...
return rootView;
}
That is all... at this point, if you have enough experience dealing with CustomArrayAdapters and Fragments you probably got it! :D
From the Android Documentation : "A Fragment represents a behavior or a portion of user interface in an Activity. You can combine multiple fragments in a single activity to build a multi-pane UI and reuse a fragment in multiple activities."
For your activity, do you want to add 2 fragments where the first one displays a listView (= ListFragment and the other one is in the right and is shown only when the user clicks on an item (from the first fragment or listView) ?
Instead of using ListFragment, you can use RecyclerView, Android has documentation on that:
https://developer.android.com/training/basics/fragments/creating.html#AddInLayout
I am new in Android programming.
I created the main Activity of my app style google shop ussing ActionBarSherlock and a NavigationTabs, with fragments, each referencing another activity (Fragment 1 Fragment 2, etc) and each fragment inflating a layout.
However, I'm used to create layouts in xml and then customize them in java. To put a different text depending on the time of day, or according to some data in a database, giving function to buttons, etc.. But in a Fragment Class, I can not even use setContentView to work with each text or button, and set the context for using my database is giving me problems.
How I can customize a xml layout in a fragment?
Or what would be the right thing to do?
Here my Fragment:
public class Fragment1 extends SherlockFragment{
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
return inflater.inflate(R.layout.menu, container, false);
}
This is more simple then you think. onCreateView instanciate au returns the view for your Fragment. As you said, in a simple Activity you set (and instanciate) the view with setContentView() and then you get your Views with findViewById().
findViewById() asks for the view to return the view item that you want, you can call it from your view before returning it. Like this:
public class Fragment1 extends SherlockFragment{
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
View v = inflater.inflate(R.layout.menu, container, false);
// For example, getting a TextView
TextView tv = (TextView) v.findViewById(R.id.myTextView);
// do your job
return v;
}
so far so good, you just need to use the view you are inflating to get everything.
here is an example
View v = inflater.inflate(R.layout.menu, container, false);
Button b = (Button)v.findViewById(r.id.button1);
return v;
inside onActivityCreated you could use:
View mView = getView();
TextView textView = (TextView) view.findViewById(R.id.theIdOfTextView);
where theIdOfTextView is declared inside R.layout.menu.
getView() returns the View you inflated inside onCreateView. You use it only after onCreateView has been executed
When a layout , which is defined for a Fragment and used inside setContentView() method and it has no relation with Activity .
then why we need Activity Reference to access it .
so I want to create a ListView , inside a Fragment . than i have to create it inside Activity layout or inside Fragment layout .
Hey Neil , i have a question because every time I have made a mistake because , i am performing this
TextView txt = ( TextView ) getActivity().findViewById(R.id.txt);
txt.setText("nayak nahi , khalnayak hun mein");
inside oncreateView() so it is creating problem but when ever i am implementing this inside
onActivityCreated() , it is working , so can you please tell me Why this is happening .
if you want to find the view by getActivity(), you should do that after onCreateView is called, because till onCreateView is called the view of fragment is null. So you can do:
#Override
public void onResume() {
super.onResume();
TextView txt = ( TextView ) getActivity().findViewById(R.id.txt);
txt.setText("nayak nahi , khalnayak hun mein");
}
You can define a ListView in a layout for your Fragment. Try something like this in your fragment to define a alternative layout
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
_baseView = inflater.inflate(R.layout.yourlayout, null); //where base view is your upper most parent in your layout
return _baseView;
}
Then in your onActivityCreated you can use _baseView.findViewById('yourListView') to set your ListView. I don't know if this is best practice but it works perfectly for me.
In Fragment you should use its View but getActivity:
public View onCreateView(…){
View rootView = inflater.inflate(R.layout.listview_xml_file, container, false);
ListView ListNewsBelarus = (ListView) rootView.findViewById(R.id.listViewId);
return rootView;
}
I have a working tablet application which I am now trying to make work on phones too.
On a table there is two fragments on the screen a list fragment and a details fragment.
When on a phone the list fragment appears and creates a new activity when a list item is pressed.
This activity simply creates the fragment in the onCreate() method and commits it to the screen as follows.
// Place an DeallDetailsFragment as our content pane
DealDetailsFragment f = new DealDetailsFragment();
getFragmentManager().beginTransaction().add(android.R.id.content, f).commit();
getFragmentManager().executePendingTransactions();
This is working as expected however from within this activity I need to tell the fragment what details to load and display. In my DealDetailsFragment class I have a updateDeal() method which updates the content as follows.
if (deal==null) { // could be null if user presses the loading deals list item before it loads
return;
}
this.deal=deal;
if (dealTitle==null) { // get the view objects only once
holder = new ViewHolder();
holder.dealHeat=(TextView) getView().findViewById(R.id.dealDetails_heat_textView);
holder.dealPrice=(TextView) getView().findViewById(R.id.dealDetails_price_textView);
holder.dealRetailer=(TextView) getView().findViewById(R.id.dealDetails_retailer_textView);
holder.dealTitle=(TextView) getView().findViewById(R.id.dealDetails_title_textView);
holder.dealDesc=(TextView) getView().findViewById(R.id.dealDetails_desc_textView);
holder.goToButton= (LinearLayout) getView().findViewById(R.id.dealDetails_goToDeal);
holder.dealImage=(ImageView) getView().findViewById(R.id.dealDetails_imageView);
holder.postedBy=(TextView) getView().findViewById(R.id.dealDetails_poster_textView);
holder.datePosted=(TextView) getView().findViewById(R.id.dealDetails_date_textView);
getView() is returning null when the application is ran on a phone where there is only a single fragment shown.
Any ideas? Unfortunately, there is not many fragment examples available online.
Move your method call to be executed during onCreateView, and use the view you are inflating for reference instead of getView(). See the fragment lifecycle for more information: https://developer.android.com/guide/components/fragments.html#Creating
and the documentation of getView() that explains why it returns null before onCreateView(LayoutInflater, ViewGroup, Bundle) returns:
getView()
Get the root view for the fragment's layout (the one returned by onCreateView(LayoutInflater, ViewGroup, Bundle)), if provided.
https://developer.android.com/reference/android/app/Fragment.html#getView()
Moving the method to onCreateView() did not help me.so... Create a global variable mView
protected View mView;
and in onCreateView()
#Override
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
Log.d(TAG, "oncreateView");
super.onCreateView(inflater, container, savedInstanceState);
View view = inflater.inflate(R.layout.activity_secure_cloud_drive_folder, container, false);
this.mView = view;
return view;
}
and the replace all your getView() with mView
You can fix that by putting your code inside the onViewCreated()-method, which you should override. Don't forget to call super() on it.
You must check the Android Lifecycle to understand WHY is it null on
onAttach(...) function.
The first function called when fragment is created is added is onAttach(), but actually no view has been created. That's why null is returned when you try to access within this call.
Next function is onCreate()... but there is no view created yet!!!!
The third function called is onCreateView(), and it's here where you have to indicate which is the view attached to this fragment.... And it's only from this call where a view object exists and can be accessed.
Read and learn the full lifecycle here.
Greetings
Because onCreate() is called before onCreateView() , whether you inflate a view in onCreateView() or not, you'll get nothing through getView() in onCreate(), because in that time , onCreate() has not been called yet .
it becomes null basically because you call getview() before the view being inflated. Create a View object and fill using inflaterand then find your UI element see code below
View view = inflater.inflate(R.layout.fragment_albumslist, container, false);
TextView t= (TextView)view.findViewById(R.id.txtTest);
t.setText(strtext);
return view;