从ViewPager活动刷新片段中的ListView崩溃

Question

I have an Activity with a ViewPager with 2 fragments inside it. One fragment is for adding items to ListView and the other fragment contains the ListView. Right now I have to restart the app to refresh the ListView once the items are added but I am trying to fix that. Here's how:

I'm trying to call the method to refresh ListView from ViewPager like this:

@Override
public void onPageSelected(int position) {
    library.populateListView(getApplicationContext(), library.lView); //this is line 47
    aBar.setSelectedNavigationItem(position);
}

This is the populateListView method inside library fragment:

public void populateListView(Context context, ListView listView){   
    CustomListViewAdapter customAdapter = new CustomListViewAdapter(getDatabaseArrayList(context), getActivity());  
    listView.setAdapter(customAdapter); //this is line 122
    customAdapter.notifyDataSetChanged();
}

And the getDatabaseArrayList method code:

private ArrayList<RecordDetails> getDatabaseArrayList(Context context){
    DatabaseHandler dbHandler = new DatabaseHandler(context);
    Cursor c = dbHandler.getAllRecordedFiles();
    ArrayList<RecordDetails> components = new ArrayList<RecordDetails>();
    RecordDetails element;
    if(c.moveToFirst()){
        element = new RecordDetails();
        element.setTitle(c.getString(c.getColumnIndex(SQLiteHelper.MUSIC_NAME)));
        element.setDate(c.getString(c.getColumnIndex(SQLiteHelper.MUSIC_DATE)));
        element.setDuration(c.getString(c.getColumnIndex(SQLiteHelper.MUSIC_DURATION)));
        components.add(element);

        while (c.moveToNext())
        {
            element = new RecordDetails();
            element.setTitle(c.getString(c.getColumnIndex(SQLiteHelper.MUSIC_NAME)));
            element.setDate(c.getString(c.getColumnIndex(SQLiteHelper.MUSIC_DATE)));
            element.setDuration(c.getString(c.getColumnIndex(SQLiteHelper.MUSIC_DURATION)));
            components.add(element);
        }
    }
    return components;
}

My guess is that the application is crashing because I'm calling ListView from ViewPager activity like library.lView which probably returns null . But how do I fix that? I tried to declare a new ListView variable inside the ViewPager activity but it crashed probably because the activity doesn't include the ListView itself.

Here's the logcat output if it helps:

03-04 08:43:44.092: E/AndroidRuntime(1779): FATAL EXCEPTION: main
03-04 08:43:44.092: E/AndroidRuntime(1779): java.lang.NullPointerException
03-04 08:43:44.092: E/AndroidRuntime(1779):     at com.matejhacin.beautifulvoicerecorder.LibraryFragment.populateListView(LibraryFragment.java:124)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at com.matejhacin.beautifulvoicerecorder.MainActivity$1.onPageSelected(MainActivity.java:46)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.support.v4.view.ViewPager.scrollToItem(ViewPager.java:567)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:551)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.support.v4.view.ViewPager.onTouchEvent(ViewPager.java:2015)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.View.dispatchTouchEvent(View.java:7384)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2205)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1940)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2211)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1954)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2211)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1954)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2211)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1954)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1966)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1418)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.app.Activity.dispatchTouchEvent(Activity.java:2424)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1914)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.View.dispatchPointerEvent(View.java:7564)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:3883)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:3778)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3379)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3429)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3398)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3483)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3406)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3540)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3379)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3429)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3398)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3406)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3379)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:5419)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:5399)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:5370)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:5493)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:182)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.os.MessageQueue.nativePollOnce(Native Method)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.os.MessageQueue.next(MessageQueue.java:132)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.os.Looper.loop(Looper.java:124)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at android.app.ActivityThread.main(ActivityThread.java:5103)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at java.lang.reflect.Method.invokeNative(Native Method)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at java.lang.reflect.Method.invoke(Method.java:525)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
03-04 08:43:44.092: E/AndroidRuntime(1779):     at dalvik.system.NativeStart.main(Native Method)

Let me know if I need to post the full logcat because I only posted the part I find the most important.

UPDATE------------------------------

Full onCreateView code:

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    View v = inflater.inflate(R.layout.fragment_library, container, false);

    // ListView
    lView = (ListView) v.findViewById(R.id.listView);
    lView.setOnItemClickListener(this);
    registerForContextMenu(lView);

    //Other variables
    components = new ArrayList<RecordDetails>();
    components = getDatabaseArrayList(getActivity());
    db = new DatabaseHandler(getActivity());
    mp = new MediaPlayer();
    playPause = (Button) v.findViewById(R.id.playPause);
    playPause.setOnClickListener(this);
    sBar = (SeekBar) v.findViewById(R.id.seekBar1);
    sBar.setOnSeekBarChangeListener(this);
    seekHandler = new Handler();

    populateListView(getActivity());
    seekHandler.post(run);

    return v;
}

UPDATE 2---------------

Library Fragment XML code:

<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:background="@drawable/gradient_background"
tools:context=".LibraryFragment" >

<ListView
    android:id="@+id/listView"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_above="@+id/seekBar1"
    android:layout_below="@+id/view1"
    android:layout_centerHorizontal="true"
    android:focusable="false"
    android:focusableInTouchMode="false" >

</ListView>

<View
    android:id="@+id/view1"
    android:layout_width="wrap_content"
    android:layout_height="40dp"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true"
    android:background="@drawable/gradient_shadow_transparent" />

<SeekBar
    android:id="@+id/seekBar1"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_alignParentLeft="true"
    android:layout_marginBottom="53dp"
    android:layout_marginLeft="40dp"
    android:layout_marginRight="40dp" />

<Button
    android:id="@+id/playPause"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_centerHorizontal="true"
    android:text="Play" />

<TextView
    android:id="@+id/current"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBottom="@+id/seekBar1"
    android:layout_alignParentLeft="true"
    android:text="0:03"
    android:layout_marginLeft="5dp" />

<TextView
    android:id="@+id/duration"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBottom="@+id/seekBar1"
    android:layout_alignParentRight="true"
    android:text="0:17"
    android:layout_marginRight="5dp" />

Answer 1

I think you dont need to send the listview from ViewPagerActivity. Keep instance of listview in your library fragment itself, store it in onCreateView.

Change your populateListView to

public void populateListView(Context context){   
    CustomListViewAdapter customAdapter = new CustomListViewAdapter(getDatabaseArrayList(context), getActivity());  
    lView.setAdapter(customAdapter); //this is line 122
    customAdapter.notifyDataSetChanged();
}

Answer 2

If this code is in fragment then you need to change from

@Override
public void onPageSelected(int position) {
 library.populateListView(getApplicationContext(), library.lView); //this is line 47
 aBar.setSelectedNavigationItem(position);
}

to

@Override
public void onPageSelected(int position) {
 library.populateListView(getActivity(), library.lView); //this is line 47
 aBar.setSelectedNavigationItem(position);
}

you have to also change here because in your populateListView there is two parameters and while you are executing only with Context. So change it.

  populateListView(getActivity());

to

  populateListView(getActivity() , lv);

I think problem might be here

   components = getDatabaseArrayList(getActivity());
   db = new DatabaseHandler(getActivity());

getDatabaseArrayList is your function which is executing and after that you have initialize your Database class. So it will be crashed here. So change

   db = new DatabaseHandler(getActivity());
   components = getDatabaseArrayList(getActivity());

Have you tried with this??

  public void populateListView(Context context){   
   CustomListViewAdapter customAdapter = new CustomListViewAdapter(components, getActivity());  
   lView.setAdapter(customAdapter); //this is line 122
   customAdapter.notifyDataSetChanged();
  }

Answer 3

From what I understood from your code is that you are trying to refresh the listView with the new data and this leads your app to be crashed.

To refresh your listview safely you need to create a method in your customAdapter called setNewData(ArrayList<object> newData) . Replace the object with the data type you are using and in this method do the following:

public void setNewDAta(ArrayList<object> newData){
    this.data = newData;
}

And from you main activity make the customAdapter a global vairable by declaring it in the start of your activity to ensure that you are using only one and create a method to pass the new data to the adapter and refresh it as following:

public void setListViewData(ArrayList<object> newData){
    customAdapter.setNewDAta(newData);
    customAdapter.notifyDataSetChanged();
}