Why I get UnsupportedOperationException in android?

Question

public class SeparatedListAdapter extends BaseAdapter {  

    public final Map<String,Adapter> sections = new LinkedHashMap<String,Adapter>();  
    public final ArrayAdapter<String> headers;  
    public final static int TYPE_SECTION_HEADER = 0;  

    public SeparatedListAdapter(Context context) {  
        headers = new ArrayAdapter<String>(context, R.layout.list_header);  
    }  

    public void addSection(String section, Adapter adapter) {  
        this.headers.add(section);  
        this.sections.put(section, adapter); }  

    public Object getItem(int position) {  
       for(Object section : this.sections.keySet()) {  
            Adapter adapter = sections.get(section);  
            int size = adapter.getCount() + 1;  
             // check if position inside this section   
            if(position <= 0) return section;  

          if(position < size){
                return adapter.getItem(position - 1);  
            }
            // otherwise jump into next section  
            position -= size;  
        }  
        return null;  
    }  
    public int getCount() {  
        // total together all sections, plus one for each section header  
        int total = 0;  
        for(Adapter adapter : this.sections.values())  
            total += adapter.getCount() + 1;  
        return total;  
    }   
    public int getViewTypeCount() {  
        // assume that headers count as one, then total all sections  
        int total = 1;  
       for(Adapter adapter : this.sections.values())  
            total += adapter.getViewTypeCount();  
        return total;  
    } public int getItemViewType(int position) {  
        int type = 1;  
       for(Object section : this.sections.keySet()) {  
            Adapter adapter = sections.get(section);  
           int size = adapter.getCount() + 1;  // check if position inside this section   
            if(position == 0) return TYPE_SECTION_HEADER;  
            if(position < size) return type + adapter.getItemViewType(position - 1);  
           // otherwise jump into next section  
            position -= size;  
            type += adapter.getViewTypeCount();  
        }  
        return -1;  
    }  
    @Override  public View getView(int position, View convertView, ViewGroup parent) {  
        int sectionnum = 0;  
        for(Object section : this.sections.keySet()) {  
            Adapter adapter = sections.get(section);  
            int size = adapter.getCount() + 1;  
            // check if position inside this section   
            if(position == 0) return headers.getView(sectionnum, convertView, parent);

Here is an Exception

        if(position < size) return adapter.getView(position - 1, convertView, parent);                
        // otherwise jump into next section  
        position -= size;  
        sectionnum++;  
    }  
    return null;  
}

I don't understand why i get this exception in this line...Please Help me~ I heard this problem causes by List<> but, I couldn't find what is wrong in my coding

score 0 · Answer 1 · edited May 23 '17 at 12:06

Where are you assigning a value to headers? What's most likely happening is that this is a ArrayAdapter backed by a read-only ArrayList.

This can happen for example when you run

this.headers = new ArrayAdapter(context, resource, Arrays.asList(T... array))

which returns a custom Array.ArrayList that is read-only. See here for asList documentation:

Returns a fixed-size list backed by the specified array.

This means you cannot run a .add() method on the list. For solution, see this related StackOverflow question.

Why I get UnsupportedOperationException in android?

1 Answers1