I am relatively new to Android. I am writing an app that uses a fragment in the main activity. This fragment also acts like a location listener and implements the onLocationChange method. This is because, based on location changes new text views are being added to this fragment.
The onCreateView method in the fragment has its scroll view created that is added to the main activity. In the same onCreateView method, I also capture the context and the linear layout tag that is present in the fragment's layout xml where I would like to insert the text views that get created in onLocationChange method.
The issue I am seeing is the context and the layout values are null in onLocationChanged method and the updateView method. Using the debugger I confirmed that they do have non-null values in the onCreateMethod only.
Here is the code snippet for the fragment class:
public class ResultsFragment extends Fragment implements LocationListener,OnCompleteListener {
private LoadPlaces loadPlaces;
HashMap<String, Double> map=new HashMap<String, Double>();
LinearLayout layout;
Context context;
Activity activity;
ScrollView view;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
view =(ScrollView)inflater.inflate(R.layout.scroll_view, container, false);
layout=(LinearLayout)view.findViewById(R.id.resultsView);
context=view.getContext();
return view;
}
#Override
public void onLocationChanged(final Location location) {
loadPlaces=new LoadPlaces(context); //context is null here
loadPlaces.setOnCompleteListener(this);
loadPlaces.execute(String.valueOf(location.getLatitude()),String.valueOf(location.getLongitude()));
}
private void updateResultView(){
String status=loadPlaces.getResultStatus();
if("OK".equals(status)){
for (Place p:loadPlaces.getPlacesResult()){
TextView txt=new TextView(context); //context is null here
txt.setText(p.name);
txt.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT,LayoutParams.WRAP_CONTENT));
layout.addView(txt); //layout is null here
}
}
}
#Override
public void onComplete(String result) {
updateResultView();
}
here is the fragment's layout xml:
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/results"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:fillViewport="true"
android:scrollbars="vertical"
android:scrollbarAlwaysDrawVerticalTrack="true"
android:clickable="true"
android:background="#color/grey"
android:layout_marginTop="25dip">
<LinearLayout android:id="#+id/resultsView"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="wrap_content">
</LinearLayout>
And this is the main activity's xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
android:padding="30dip"
android:layout_gravity="center"
android:background="#color/background">
<fragment android:name="com.app.xxx.ResultsFragment"
android:id="#+id/headlines_fragment"
android:layout_weight="1"
android:layout_width="fill_parent"
android:layout_height="0dp"/>
For your information, the activity that holds the fragment is never paused/killed. It is always visible while the location service runs in the background. So in this process, I don't think the fragment is getting destroyed.
Am i approaching this problem incorrectly? Is there a better way to access or save the fragment's context and use it later? Any tips will be helpful.
Thanks in advance.
Change to:
#Override
public void onLocationChanged(final Location location) {
if(getActivity()!=null){
loadPlaces=new LoadPlaces(getActivity()); //context is null here
loadPlaces.setOnCompleteListener(this);
loadPlaces.execute(String.valueOf(location.getLatitude()),String.valueOf(location.getLongitude()));
}
}
The problem is location change listener is called before onCreateView.
You can ignore all the onLocationChanged calls until your fragment is attached to Activity by using above function.
public void onAttach(android.app.Activity activity) {
super.onAttach(activity);
context = (Context)getActivity();
};
Related
I am using fragments to update a text view I have so when the person clicks a button the text view moves on to the next question. I'm not sure if I am doing the correct work in one fragment instead of the other. My current screen looks like this:
I will probably have to add some more buttons/widgets to this but should I be adding it into the XML for the fragment or the fragment container?
Here is XML for fragment actions:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/fragment_question_layout1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:padding="16dp"
tools:context=".FragmentActions"
>
<!-- this is where fragments will be shown-->
<FrameLayout
android:id="#+id/question_container1"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="4"
android:scaleType="centerInside" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">
<Button
android:id="#+id/questions_yes1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:gravity="center"
android:text="#string/yes" />
<Button
android:id="#+id/questions_no1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:gravity="center"
android:text="#string/no" />
</LinearLayout>
</LinearLayout>
And here is the fragment details:
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/button_layout1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginTop="10dp"
tools:context=".FragmentDetails">
<!--Blank Fragment Layout-->
<TextView
android:id="#+id/questions_text_view1"
android:layout_width="match_parent"
android:layout_height="91dp"
android:gravity="center"
android:textAlignment="center"
/>
</FrameLayout>
Updated FragmentDetails
public class FragmentDetails extends Fragment {
private final String TAG = getClass().getSimpleName();
private List<Integer> mQuestionIds;
private int mListIndex;
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
//Inflate the fragment layout
View rootView = inflater.inflate(R.layout.fragment_details, container, false);
//Get a reference to the textView in the fragment layout
final TextView textView = (TextView) rootView.findViewById(R.id.questions_text_view1);
if (mQuestionIds != null) {
textView.setText(mQuestionIds.get(mListIndex));
//Increment the position in the question lisy as long as index is less than list length
if (mListIndex < mQuestionIds.size() - 1) {
mListIndex++;
setmQuestionIds(QuestionList.getQuestions());
setmListIndex(mListIndex);
} else {
//end of questions reached
textView.setText("End of questions");
}
//Set the text resource to display the list item at that stored index
textView.setText(mQuestionIds.get(mListIndex));
}
else {
//Log message that list is null
Log.d(TAG, "No questions left");
}
//return root view
return rootView;
}
public void setmQuestionIds (List < Integer > mQuestionIds) {
this.mQuestionIds = mQuestionIds;
}
public void setmListIndex ( int mListIndex){
this.mListIndex = mListIndex;
}
}
Fragment Actions activity
public class FragmentActions extends AppCompatActivity {
#Override
protected void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fragment_actions);
Button yes = findViewById(questions_yes1);
// Only create new fragments when there is no previously saved state
if (savedInstanceState == null) {
//Create Question Fragment
final FragmentDetails fragmentDetails = new FragmentDetails();
fragmentDetails.setmQuestionIds(QuestionList.getQuestions());
yes.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
//set the list of question Ids for the head fragent and set the position to the second question
//Fragment manager and transaction to add this fragment
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.question_container1, fragmentDetails)
.commit();
}
});
}
}
}
If your Buttons remain the same while the TextView changes, you may add your Buttons to the fragment container.
Remember that, your fragments will be presented inside the FrameLayout of the fragment container. You gotta keep your Buttons, outside the FrameLayout.
Or if you want to have different Buttons for different fragments (Questions, in your case), you can also add the Buttons to the fragments. But in that case, you gotta add them separately to each of the fragments.
I guess there's no right answer to your question. You could try different approaches.
Maybe you could implement the buttons in the fragment container, as #smmehrab pointed out. I see this as a more difficult solution, because when you click on an item from the container you can manage the views of the container, not the fragment's views. You would get NullPointer if I recall correctly. This happens because the context when the button is clicked in the fragment container is different than the context when clicking from within the fragment. So you should implement an interface on the fragment container that listens to clicks, and the fragment catches the click. You could do this, and I actually am doing it in my current app, but I have no choice.
You could instead use Motion Layout (which extends from Constraint Layout) as the root view of your fragment, instead of CardView. This way you could set all the fragment's views with a flat hierarchy (flat hierarchies improves rendering time, so that's an improvement, and you can use CardView as one child) and set the buttons right there, in the Motion Layout (remember, the motion layout would be the fragment's root view). You could set the click listener right there and implement animations between different textViews.
I'm sure there are plenty of other solutions, take this only as a contribution.
If you're unfamiliar with Motion Layout you can just google it, android official documentation about it is great.
So I am still fairly new to working with Android Studio and everything in it. I have been stuck on trying to get fragments to communicate directly with each other. Here I'm simply just trying to set the TextView text element within one of my fragments. I have looked for hours and tried a lot, but I'm not sure what to do. Also, I am implementing my fragments through code in a FrameLayout.
Here is my fragment whose text value I'm trying to edit:
public class ReceivingFrag extends Fragment {
TextView sender;
public void updateText(String text) {
sender.setText(text);
}
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.frag_sender, container, false);
sender = (TextView) v.findViewById(R.id.sender);
return v;
}
}
I believe my root problem is that getView() and sender both return Null. I also understand that fragments are not technically views, but rather aid in the layout of views and ViewGroups. Any help is appreciated.
Not sure if it helps, but this is the method that calls the updateText() method within the ReceivingFrag class.
public void sendText(String text){
ReceivingFrag frag = new ReceivingFrag();
getSupportFragmentManager().beginTransaction().add(R.id.receiving_container, frag).commit();
getSupportFragmentManager().executePendingTransactions()
frag.updateText(text);
}
**Edit:
This is my MainActivity class that is calling and creating the Fragment:
public class MainActivity extends AppCompatActivity implements SendingFragment.TextClicked {
private static final String TAG = MainActivity.class.getSimpleName();
public final static String EXTRA_MESSAGE = "com.example.myfirstapp.MESSAGE";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
String[] myStringArray = {"Hello", "Nice To See You", "Bye"};
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, myStringArray);
ListView listView = (ListView) findViewById(R.id.mobile_list);
listView.setAdapter(adapter);
sendText("Hello");
}
#Override
public void sendText(String text){
ReceivingFrag frag = new ReceivingFrag();
getSupportFragmentManager().beginTransaction().add(R.id.receiving_container, frag).commit();
getSupportFragmentManager().executePendingTransactions();
frag.updateText(text);
}}
**Edit 2:
This is the MainActivity layout file:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/apk/tools"
xmlns:tools2="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:weightSum="1">
<EditText android:id="#+id/edit_message"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:hint="#string/edit_message"
android:layout_weight="1" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="sendMessage"
android:text="#string/button_send"/>
</LinearLayout>
<ListView android:id="#+id/mobile_list"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
<FrameLayout
android:id="#+id/receiving_container"
android:layout_width="wrap_content"
android:layout_height="wrap_content"></FrameLayout></LinearLayout>
And this is the layout for the Fragment:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="#+id/sender"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="#string/frag_sender"
android:background="#color/gray"
android:layout_marginLeft="10dp"
android:layout_marginRight="10dp"/></LinearLayout>
Solution:
So as mentioned below, the runtime error was fixed by adding
#Override
protected void onResume() {
super.onResume();
sendText("hello");
}
to the MainActivity class. After reading from https://developer.android.com/guide/components/fragments.html#Lifecycle
I think the statement
"Once the activity reaches the resumed state, you can freely add and remove fragments to the activity. Thus, only while the activity is in the resumed state can the lifecycle of a fragment change independently."
best explains the situation and why the error initially occurred.
If you instead put the sendText() in your onResume() like this,
#Override
protected void onResume() {
super.onResume();
sendText("Hello");
}
It will not give you the Null Pointer Exception. The fragment is still null when you call on it from onCreate().
Change your Fragment to this:
public class ReceivingFrag extends Fragment {
private TextView sender;
public void updateText(String text) {
sender.setText(text);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.frag_sender, container, false);
sender = (TextView) v.findViewById(R.id.sender);
return v;
}
}
and in your activity, before calling the updateText method, make sure the fragment transaction has executed by doing:
public void sendText(String text){
ReceivingFrag frag = new ReceivingFrag();
getSupportFragmentManager().beginTransaction().add(R.id.receiving_container, frag).commit();
getSupportFragmentManager().executePendingTransactions();
frag.updateText(text);
}
i am trying to hide/show Button in fragment from Activity but it give me following exception.
android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
Home Activity
public class HomeActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
CategoryFragment frag=(CategoryFragment) activity.getSupportFragmentManager()
.findFragmentByTag("cat_frag");
Button newDesigns= (Button) frag.getView().findViewById(R.id.new_designs);
newDesigns.setVisibility(View.VISIBLE);
}
}
Category Fragment
public class CategoryFragment extends Fragment{
Button newDesigns;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_category, null);
newDesigns= (Button) v.findViewById(R.id.new_designs);
}
}
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#CCCCCC">
<TextView
android:id="#+id/list_name"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:background="#drawable/shape_logo_bg"
android:gravity="center"
android:padding="5dp"
android:textColor="#android:color/white"
android:textSize="18sp" />
<Button
android:id="#+id/new_designs"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#id/list_name"
android:background="#color/edit_button_color"
android:padding="10dp"
android:text="#string/new_designs"
android:textColor="#color/btn_text_color"
android:layout_centerHorizontal="true"
android:layout_marginTop="5dp"
android:visibility="gone"
/>
</RelativeLayout>
Code is too large to be posted here. Thats why i have only posted the code where i am finding an issue.
I am able to get newDesigns BUTTON instance.What is shocking for me is if try to play with button instance (VISIBLE/GONE) it gives me above mentioned exception.
Help is appreciated.
You shouldn't play with a view of the Fragment while you are in a Activity directly. You will not know what the view's state will be and this can potentially lead to issues you can't even think of(beleive me i faced many). To interact with the activity's views, make an interface:
public interface AccessFragmentViews{
public void setVisibilityForButton(boolean bool);
//any other methods that you need
}
Now implement this inside the fragment class and override the method.
class YourFragment implements AccessFragmentViews{
.
.
public void serVisibilityForButton(boolean shouldHide){
if(shouldHide){
yourButton.setVisibility(View.GONE);
}else{
yourButton.setVisibility(View.VISIBLE);
}
}
}
Now you can interact safely with the views of the fragment within a activity using this interface. Make sure that the fragment is alive before doing so though ;) accessing child's view are prone to WindowLeakedExceptions and illegalstateexceptions
In the activity use it as follows:
you can get the fragment reference by either finding it by its tag or by using the reference you used to create the fragment
//NOTE: it is very very dangerous to do the accessing on a fragment views from an activity
//first the alive check then the logic
if(yourFragmentReference!=null){
((AccessFragmentViews)yourFragmentReference).setVisibilityForButton(true);// or false if you want to make it visible
}
Add a method in your fragment class
public void changeButtonVisibility(boolean visibility){
if(visibility){
newDesigns.setVisibility(View.VISIBLE);
}else{
newDesigns.setVisibilty(View.GONE);
}
}
and in your activity class
add this line
public class HomeActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
CategoryFragment frag=(CategoryFragment) activity.getSupportFragmentManager()
.findFragmentByTag("cat_frag");
frag.changeButtonVisibility(true);
}
}
I'm trying to develop a sign-up menu for a social app, that I'm working on. I would like the sign-up menu to consist of a PageViewer, which holds five fragments. The last three fragments contains a ListView, where the user can 'check' information about them selves. The XML is here:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:minWidth="25px"
android:minHeight="25px"
android:id="#+id/layoutSignupLists">
<TextView
android:text="Add something here"
android:textAppearance="?android:attr/textAppearanceMedium"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:id="#+id/signupListDescription" />
<ListView
android:id="#+id/interestListView"
android:layout_below="#id/signupListDescription"
android:layout_height="match_parent"
android:layout_width="match_parent" />
</RelativeLayout>
This layout is inflated, when the last three fragments are created as is displayed correctly. I have subscribed a delegate to the itemSelected event in the ListView as seen below:
public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
//Inflate view and find content
View view = inflater.Inflate(Resource.Layout.signupFragLayout4, container, false);
interestListView = view.FindViewById <ListView>(Resource.Id.interestListView);
var desc = view.FindViewById<TextView>(Resource.Id.signupListDescription);
//Adds the description
desc.Text = GetString(Resource.String.profile_menu_edit_interests);
//Populate ListView
interestListView.Adapter = new ArrayAdapter<string>(Activity,
Resource.Layout.CheckedListViewItem, MainActivity.InfoNames[(int)InfoType.Interest]);
interestListView.ChoiceMode = ChoiceMode.Multiple;
interestListView.ItemSelected += (object sender, AdapterView.ItemSelectedEventArgs e) =>
{
if(!Interests.Contains(e.Position))
Interests.Add(e.Position);
else
Interests.Remove(e.Position);
};
return view;
}
When putting a break-point in the delegate I find that it's never called and thus the ListView reset upon swiping right or left.
How can I make the fragment 'hold on' to the information so that it's displayed every time the fragment is shown?
Place the information in the MainActivity. You can make a simple reference to it by putting this variable in your fragment class:
MainActivity mainActivity;
And in your OnCreateView() place this to initialize it:
mainActivity = (MainActivity)Activity;
Now if you have any public variables in the mainActivity, you can reference them in the fragment like:
textView.Text = mainActivity.VariableName;
Additionally, for putting the information back in the fragment, override the 'OnResume' method like so:
public override void OnResume()
{
base.OnResume();
//Code to fill in all the information in your fragment again. I.E:
textView.Text = mainActivity.VariableName;
}
I have a simple Android app. The layout folder shows an activity_main.xml file and a fragment_main.xml file. In that fragment.xml file I have placed a button that I've named buttonTest.
<RelativeLayout 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:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
android:paddingBottom="#dimen/activity_vertical_margin"
tools:context="com.snapvest.thunderbird.app.MainActivity$PlaceholderFragment">
<LinearLayout
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true">
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="TEST"
android:id="#+id/buttonTest"
android:layout_gravity="center_horizontal" />
</LinearLayout>
in the MainActivity.java file I'm trying to gain access to that buttonTest.
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
// Get access to the buttons
final Button buttonTest = (Button)findViewById(R.id.buttonTest);
}
It compiles just fine. But when I run it the buttonTest variable comes back as a null pointer.
Why is it not finding the buttonTest object?
I think I found the solution. MainActivity.java sets up the activity_main.xml which then uses fragment_main.xml as its (initially) single, primary fragment. That's why we are supposed to actually put all of our UI for the activity primarily in fragment_main.xml (and actually put NOTHING in activity_main.xml).
Near the bottom of MainActivity.java there is a section that initializes the fragment_main.xml. And it is THERE that I need to gain access to the buttons and other objects of the UI for the fragment. Such as:
/**
* A placeholder fragment containing a simple view.
*/
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_main, container, false);
// Get access to the buttons
final Button buttonAvailableOptions = (Button)rootView.findViewById(R.id.buttonAvailableOptions);
return rootView;
}
}
Most of that, above, is automatically added by Android Studio. The part starting with "Get access to the button" is mine and is where you set up any access to or processing of the buttons and other UI objects.
The reason why findViewById() is failing to find the button is because setContentView() primes findViewById() to only look in the layout.xml file you gave to setContentView(), and your button is not located in R.layout.activity_main. If your button is located in the Fragment (which it appears to be) then you should be accessing and manipulating it from the Fragment, not the Activity. This ensures that your Activity and Fragment logic stay decoupled, allowing you to re-use the Fragment with different Activities.
You can use like this.
final Button buttonAvailableOptions = getActivity().findViewById(R.id.buttonAvailableOptions);