Issues with personal listView Adapter

I'm having some troubles using my own Adapter class for creating a ListView with delimiter. I'm a beginner in Android development so I really can't fix it alone.

I want to create a listview with the same layout as seen on this web site, and I also want my items to be alphabetically ordered.

So I create two Adapter, one for adding the delimiters, and the other one for handling the specific layout of each item.

The class ListeMusicContainer is an ArrayList sorted alphabetically by name.

Each one works perfectly fine separately, but when I try out both, I get a runtime error.

The error doesn't appear when the application starts, only when I try to scroll (so I guess I'm almost good).

I really don't why I get this error when scrolling. How can this be solved?

Here is the Adapter i use to create a ListView with delimiter

abstract public class MusicAdapter extends BaseAdapter{

abstract protected View getHeaderView(String caption, int index,
        View convertView, ViewGroup parent);
private List<Section> sections = new ArrayList<Section>();

private static int TYPE_SECTION_HEADER = 0;

public MusicAdapter() {
    super();
}

public void addSection(String caption, ItemAdapter adapter){
    sections.add(new Section(caption, adapter));
}

public Object getItem(int position){
    for (Section section : this.sections){
        if (position == 0){
            return section;
        }

        int size = section.adapter.getCount() + 1;
        if (position < size){
            return section.adapter.getItem(position - 1);
        }
        position -= size;
    }
    return null;
}

public int getCount(){
    int total = 0;

    for (Section section : this.sections){
        total += section.adapter.getCount() + 1;
    }
    return total;
}

public int getItemViewType(int position){
    int typeOffset = TYPE_SECTION_HEADER + 1;

    for (Section section : this.sections) {
        if (position == 0) {
            return (TYPE_SECTION_HEADER);
        }

        int size = section.adapter.getCount() + 1;

        if (position < size) {
            return (typeOffset + section.adapter
                    .getItemViewType(position - 1));
        }

        position -= size;
        typeOffset += section.adapter.getViewTypeCount();
    }

    return -1;
}

public boolean areAllItemsSelectable(){
    return false;
}

public boolean isEnabled(int position) {
    return (getItemViewType(position) != TYPE_SECTION_HEADER);
}

@Override
public View getView(int position, View convertView, ViewGroup parent){
    int sectionIndex = 0;

    for (Section section : this.sections){
        if (position == 0){
            return (getHeaderView(section.caption, sectionIndex, convertView, parent));
        }
        int size = section.adapter.getCount() + 1;

        if (position < size){
            return (section.adapter.getView(position - 1, convertView,
                    parent));
        }
        position -= size;
        sectionIndex++;
    }
    return null;
}

@Override
public long getItemId(int position){
    return position;        
}

class Section {
    String caption;
    ItemAdapter adapter;

    Section(String caption, ItemAdapter adapter) {
        this.caption = caption;
        this.adapter = adapter;
    }
}
}

And here is the one I use for each item :

public class ItemAdapter extends BaseAdapter{

private ListeMusicContainer<Music> mList;
private LayoutInflater mInflater;

public ItemAdapter(Context context, ListeMusicContainer<Music> musics){
    mInflater = LayoutInflater.from(context);
    mList = musics;
}

@Override
public int getCount() {
    return mList.size();
}

@Override
public Obje开发者_如何学Cct getItem(int position) {
    return position;
}

@Override
public long getItemId(int position) {
    return position;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder holder;

    if (convertView == null){
        convertView = mInflater.inflate(R.layout.list_item, null);

        holder = new ViewHolder();
        holder.nom = (TextView) convertView.findViewById(R.id.nomAlbum);
        holder.genre = (TextView) convertView.findViewById(R.id.genreAlbum);

        convertView.setTag(holder);
    }
    else{
        holder = (ViewHolder) convertView.getTag();
    }
    holder.nom.setText(mList.getItem(position).getNom());
    holder.genre.setText(mList.getItem(position).getGenre());

    return convertView;
}

static class ViewHolder{
    TextView nom;
    TextView genre;
}

}

Here is how i initialize my layout :

public class TestView extends ListActivity {
/** Called when the activity is first created. */

private ListView mListView;
private static String[] items;
private XmlDataParser mParser;
private ListeMusicContainer<Music> mList;


private MusicAdapter mAdapter = new MusicAdapter() {
    protected View getHeaderView(String caption, int index,
            View convertView, ViewGroup parent) {
        TextView result = (TextView) convertView;

        if (convertView == null) {
            result = (TextView) getLayoutInflater().inflate(
                    R.layout.header, null);
        }

        result.setText(caption);

        return (result);
    }
};

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    mParser = new XmlDataParser();
    mList = mParser.parseXml(this);

    ListeMusicContainer<Music> groupe = new ListeMusicContainer<Music>();
    String currLetter = null;

    for (int i = 0; i < mList.size(); i++){
        if (!mList.getItem(i).getLabel().equalsIgnoreCase(currLetter) && currLetter != null){
            mAdapter.addSection(mList.getItem(i).getLabel().toUpperCase(), new ItemAdapter(this, groupe));
            groupe = new ListeMusicContainer<Music>();
            currLetter = mList.getItem(i).getLabel();
        }
        if (currLetter == null){
            currLetter = mList.getItem(i).getLabel();
        }

        groupe.addData(mList.getItem(i));
    }

    setListAdapter(mAdapter);

}
}

edit : in logcat, here is what I got in logcat when running the application :

I/ActivityManager(   42): Displayed activity com.view/.TestView: 1480 ms (total
1480 ms)
D/dalvikvm(  975): GC_EXTERNAL_ALLOC freed 1214 objects / 78504 bytes in 96ms
D/AndroidRuntime(  975): Shutting down VM
W/dalvikvm(  975): threadid=1: thread exiting with uncaught exception (group=0x4
001d800)
E/AndroidRuntime(  975): FATAL EXCEPTION: main
E/AndroidRuntime(  975): java.lang.NullPointerException
E/AndroidRuntime(  975):        at com.view.ItemAdapter.getView(ItemAdapter.java
:51)
E/AndroidRuntime(  975):        at com.view.MusicAdapter.getView(Music
Adapter.java:91)
E/AndroidRuntime(  975):        at android.widget.AbsListView.obtainView(AbsList
View.java:1294)
E/AndroidRuntime(  975):        at android.widget.ListView.makeAndAddView(ListVi
ew.java:1727)
E/AndroidRuntime(  975):        at android.widget.ListView.fillDown(ListView.jav
a:652)
E/AndroidRuntime(  975):        at android.widget.ListView.fillGap(ListView.java
:623)
E/AndroidRuntime(  975):        at android.widget.AbsListView.trackMotionScroll(
AbsListView.java:2944)
E/AndroidRuntime(  975):        at android.widget.AbsListView.onTouchEvent(AbsLi
stView.java:2065)
E/AndroidRuntime(  975):        at android.widget.ListView.onTouchEvent(ListView
.java:3315)
E/AndroidRuntime(  975):        at android.view.View.dispatchTouchEvent(View.jav
a:3766)
E/AndroidRuntime(  975):        at android.view.ViewGroup.dispatchTouchEvent(Vie
wGroup.java:897)
E/AndroidRuntime(  975):        at android.view.ViewGroup.dispatchTouchEvent(Vie
wGroup.java:936)
E/AndroidRuntime(  975):        at android.view.ViewGroup.dispatchTouchEvent(Vie
wGroup.java:936)
E/AndroidRuntime(  975):        at android.view.ViewGroup.dispatchTouchEvent(Vie
wGroup.java:936)
E/AndroidRuntime(  975):        at com.android.internal.policy.impl.PhoneWindow$
DecorView.superDispatchTouchEvent(PhoneWindow.java:1671)
E/AndroidRuntime(  975):        at com.android.internal.policy.impl.PhoneWindow.
superDispatchTouchEvent(PhoneWindow.java:1107)
E/AndroidRuntime(  975):        at android.app.Activity.dispatchTouchEvent(Activ
ity.java:2086)
E/AndroidRuntime(  975):        at com.android.internal.policy.impl.PhoneWindow$
DecorView.dispatchTouchEvent(PhoneWindow.java:1655)
E/AndroidRuntime(  975):        at android.view.ViewRoot.handleMessage(ViewRoot.
java:1785)
E/AndroidRuntime(  975):        at android.os.Handler.dispatchMessage(Handler.ja
va:99)
E/AndroidRuntime(  975):        at android.os.Looper.loop(Looper.java:123)
E/AndroidRuntime(  975):        at android.app.ActivityThread.main(ActivityThrea
d.java:4627)
E/AndroidRuntime(  975):        at java.lang.reflect.Method.invokeNative(Native
Method)
E/AndroidRuntime(  975):        at java.lang.reflect.Method.invoke(Method.java:5
21)
E/AndroidRuntime(  975):        at com.android.internal.os.ZygoteInit$MethodAndA
rgsCaller.run(ZygoteInit.java:868)
E/AndroidRuntime(  975):        at com.android.internal.os.ZygoteInit.main(Zygot
eInit.java:626)
E/AndroidRuntime(  975):        at dalvik.system.NativeStart.main(Native Method)

W/ActivityManager(   42):   Force finishing activity com.view/.TestView