android listview displays false data after scrolling (custom adapter)

I had a similar problem with multiple item types in the list. In my case the list item was either a section (label) item or a common list item.

To work with such types of lists, you should override getViewTypeCount and getItemViewType methods. Something like this:

private static final int ITEM_VIEW_TYPE_ITEM = 0;
private static final int ITEM_VIEW_TYPE_SEPARATOR = 1;

@Override
public int getViewTypeCount() {
    return 2;
}

@Override
public int getItemViewType(int position) {
    return this.getItem(position).isSection() ? ITEM_VIEW_TYPE_SEPARATOR : ITEM_VIEW_TYPE_ITEM;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    final Item item = this.getItem(position);

    if (convertView == null) {
        convertView = mInflater.inflate(item.isSection() ? R.view1 : R.view2, null);
    }

    if(item.isSection()){
        //...
    }
    else{
        //...
    }

    return convertView;
}

Then the convertView parameter will always be correct and contain that type which you need.

And another thing: you explicitly added the public Param[] params field when you already have it in the base class ArrayAdapter<Param>.

I would recommend to inherit from the BaseAdapter class.

Edit: Here is the code which you can try to use in order to make your Spinner work:

sp.setTag(p);
sp.setOnItemSelectedListener(new OnItemSelectedListener(){
public void onItemSelected(AdapterView<?> parent, View convertView, int pos, long id) {
    Param currentItem = (Param)parent.getTag();
    currentItem.setDefData(currentItem.getData().get(pos));
    currentItem.setChanged(true);
}
//...

Try to use the combination of the getTag and setTag methods. I remember that I had similar problems with event handlers and final variables, but I completely forgot the cause of them, so I can't explain exactly why this happens.