Extending ArrayAdapter in android

I need to override a getFilter() method from the class ArrayAdapter and i found the source code from here in the github

//package name

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import android.content.Context;
import android.util.Log;
import android.widget.ArrayAdapter;
import android.widget.Filter;
import android.widget.Filterable;

public class CustomAdapter<T> extends ArrayAdapter<T> implements Filterable{

    private ArrayList<T> mOriginalValues;
    private List<T> mObjects;
    private CustomFilter mFilter;
    private final Object mLock = new Object();
    public CustomAdapter(Context context, int textViewResourceId, T[] objects) {
        super(context, textViewResourceId, objects);

        mObjects = Arrays.asList(objects);
        // TODO Auto-generated constructor stub
    }

    @Override
    public Filter getFilter() {
        // TODO Auto-generated method stub
        if (mFilter == null) {
            mFilter = new CustomFilter();
        }
        return mFilter;
    }


    private class CustomFilter extends Filter {
        @Override
        protected FilterResults performFiltering(CharSequence prefix) {
            FilterResults results = new FilterResults();
            Log.d("bajji", "its ---> " + prefix);
            if (mOriginalValues == null) {
                synchronized (mLock) {
                    mOriginalValues = new ArrayList<T>(mObjects);
                }
            }

            if (prefix == null || prefix.length() == 0) {
                ArrayList<T> list;
                synchronized (mLock) {
                    list = new ArrayList<T>(mOriginalValues);
                }
                results.values = list;
                results.count = list.size();
            } else {
                String prefixString = prefix.toString().toLowerCase();

                ArrayList<T> values;
                synchronized (mLock) {
                    values = new ArrayList<T>(mOriginalValues);
                }

                final int count = values.size();
                final ArrayList<T> newValues = new ArrayList<T>();
                final ArrayList<T> approxValues = new ArrayList<T>();
                final ArrayList<T> secondApproxValues = new ArrayList<T>();


                for (int i = 0; i < count; i++) {
                    final T value = values.get(i);
                    final String valueText = value.toString().toLowerCase();
                    boolean flag = true;
                    // First match against the whole, non-splitted value
                    if (valueText.startsWith(prefixString)) {
                        newValues.add(value);
                        flag = false;
                    } else {
                        final String[] words = valueText.split(" ");
                        final int wordCount = words.length;

                        // Start at index 0, in case valueText starts with space(s)
                        for (int k = 0; k < wordCount; k++) {
                            if (words[k].startsWith(prefixString)) {
                                newValues.add(value);
                                flag = false;
                                break;
                            } 
                        }
                    }

                    if(flag) {
                        if(approxMatch(valueText, prefixString) <= 3) { //change the stuff and do a levi work
                            approxValues.add(value);
                        }
                        else {
                            final String[] words = valueText.split(" ");
                            final int wordCount = words.length;

                            // Start at index 0, in case valueText starts with space(s)
                            for (int k = 0; k < wordCount; k++) {
                                if(approxMatch(words[k], prefixString) <= 3) {
                                    //leve work
                                    secondApproxValues.add(value);
                                    break;
                                }
                            }
                        }
                    }
                }
                newValues.addAll(approxValues);
                newValues.addAll(secondApproxValues);
                results.values = newValues;
                results.count = newValues.size();
            }
            return results;
        }
        @Override
        protected void publishResults(CharSequence constraint, FilterResults results) {
            //noinspection unchecked
            mObjects = (List<T>) results.values;
            if (results.count > 0) {
                notifyDataSetChanged();
            } else {
                notifyDataSetInvalidated();
            }
        }
    }

    private int approxMatch (String s, String t) {
          // an approxmimate string matching algo
          return p;
    }
}

The problem is the getFilter method has a object of a private inner class ArrayFilter which has a method peformFiltering and i need to put a different code there so i have to overide the class. And i get an exception in the method.

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  • In the derived class which extends ArrayAdapter i created a private inner class which is similar to ArrayFilter and called it MyFilter and i get the same exception again in the method performFiltering.

    I found a solution to solve my problem. I copied all the code in ArrayAdapter class and created a new class called MyAdapter and i altered some code inside the inner class ArrayFilter and the app works the way i wanted it to. But i feel its not the best solution.

    Android has various api levels so if the array adapter is changed in different api level then i have to add those changes in my codes to. So i feel the best way is to extend the class ArrayAdapter to create MyAdapter rather than just copying and pasting the code from the ArrayAdapter

    How can i override the inner private class of a parent class..?

    Edit: The exception i get..
    Exception

    Edit2: Now i added the full code in the question. and it works perfectly if i copy and edit the array adapter.. the problem is only when i extend..!! now the code and search is working perfectly. I checked it with Log.i.. but the drop down list for auto complete suggestion in UI is not working.. i only get for the first character i type the next character filtering takes place but UI update is not taking place.

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  • 4 Solutions collect form web for “Extending ArrayAdapter in android”

    After some help from stackoverflow community i removed the exception and later i found out that the suggestions that are returned doesn’t really change because the mObjects was returned from the super class or base class. The problem was the there were two public methods getCount() and getItem(int position) which gets the count and fetches the list from mObjects from the base class. So i just have to add those two methods in my class..

    public int getCount() {
        return mObjects.size();
    }
    
    public T getItem(int position) {
        return mObjects.get(position);
    }
    

    Now mObjects of the derived class will be returned. Which are the updated in the dropdown list in the UI.

    I am not a java expert, but this solves my problem. If you have any suggestions to make the code better please add it in comments or feel free to edit the answer.!

    Update:

    You should override the toString() method in your T class and return the filter criterion string.

    For example,

    class T {
    
        String firstName;
        String lastName;
        ...
        ...
        @override
        String toString() {
            return firstName + lastName;
        }
    }
    

    By default, the toString() implementation of the Object class returns getClass().getName() + '@' + Integer.toHexString(hashCode())

    Original:

    The array list reference should be passed to the ArrayAdapter constructor. I think you are not doing this and hence its not able to get a list for filtering.

    In this sample code objects array reference is passed to the super constructor.

    public CustomAdapter(Context context, int tvResId, ArrayList<String> objects) {
        super(context, textViewResourceId, objects);
        this.objects = objects;
    }
    

    If your filtering is based on the simple strings in the list items, then you can implement TextWatcher as suggested by @Iiorry. But if the filtering is bit complex than that, then you need to implement Filterable as well.

    You don’t need to implement your own filter… just override getFilter as @Waqas suggested.

    Here’s what I did and it works.
    Feel free to adjust it to your needs…

    Hope it’ll help.

    The EditText (searchFilder):

    searchFilter.addTextChangedListener(mOnSearchBoxTextChanged);
    private TextWatcher mOnSearchBoxTextChanged = new TextWatcher() {
    
            public void afterTextChanged(Editable s) {
            }
    
            public void beforeTextChanged(CharSequence s, int start, int count,
                    int after) {
            }
    
            public void onTextChanged(CharSequence s, int start, int before,
                    int count) {
                mAdapter.getFilter().filter(s.toString());
            }
    
        };
    

    The Adapter getFilter():

        class MyAdapter extends BaseAdapter implements Filterable {
    
                //the rest of the adapter....
    
                @Override
                public Filter getFilter() {
                    if (newFilter == null) {
                        newFilter = new Filter() {
                            @Override
                            protected void publishResults(CharSequence prefix,
                                    FilterResults results) {
    
                                CLog.logD( "Friends list filtered");
    
                                mAdapter.notifyDataSetChanged();
                            }
    
                            @Override
                    protected FilterResults performFiltering(CharSequence constraint) {
                        constraint = constraint.toString().toLowerCase();
    
                        filteredFriendList = new ArrayList<FriendsListItemView>();
    
                        if (constraint!= null && constraint.toString().length() > 0) {
                            for (int i = 0; i < friendsList.size(); i++) {
                                FriendsListItemView newFriend = friendsList.get(i);
                                String name = newFriend.userName.getText().toString();
    
                                if (name.toLowerCase().contains(constraint)) {
                                    filteredFriendList.add(newFriend);
                                } 
                            }
    
                        } else {
                            if (filteredFriendList.size() == 0) {
                                filteredFriendList = friendsList;
                            }
                        }
    
                        FilterResults newFilterResults = new FilterResults();
                        newFilterResults.count = filteredFriendList.size();
                        newFilterResults.values = filteredFriendList;
                        return newFilterResults;
                    }
                };
                    }
                    return newFilter;
                }
            }
    

    Perhaps this may help you:

    import java.util.ArrayList;
    import java.util.Arrays;
    import java.util.List;
    import android.content.Context;
    import android.util.Log;
    import android.widget.ArrayAdapter;
    import android.widget.Filter;
    
    public class CustomAdapter<T> extends ArrayAdapter<T> {
    
        private final ArrayList<T> mOriginalValues;
        private List<T> mObjects;
        private CustomFilter mFilter;
        private final Object mLock = new Object();
        public CustomAdapter(Context context, int textViewResourceId, T[] objects) {
            super(context, textViewResourceId, objects);
    
            mObjects = Arrays.asList(objects);
            mOriginalValues = (ArrayList<T>) Arrays.asList(objects);
            // TODO Auto-generated constructor stub
        }
    
        @Override
        public Filter getFilter() {
            // TODO Auto-generated method stub
            if (mFilter == null) {
                mFilter = new CustomFilter();
            }
            return mFilter;
        }
    
    
        private class CustomFilter extends Filter {
            @Override
            protected FilterResults performFiltering(CharSequence prefix) {
                FilterResults results = new FilterResults();
                Log.d("bajji", "its ---> " + prefix);
    
                if (prefix == null || prefix.toString().trim().length() == 0) {
                    ArrayList<T> list;
                    synchronized (mLock) {
                        list = new ArrayList<T>(mOriginalValues);
                    }
                    results.values = list;
                    results.count = list.size();
                } else {
                    String prefixString = prefix.toString().toLowerCase();
    
                    ArrayList<T> values;
                    synchronized (mLock) {
                        values = new ArrayList<T>(mOriginalValues);
                    }
    
                    final int count = values.size();
                    final ArrayList<T> newValues = new ArrayList<T>();
                    final ArrayList<T> approxValues = new ArrayList<T>();
                    final ArrayList<T> secondApproxValues = new ArrayList<T>();
    
    
                    for (int i = 0; i < count; i++) {
                        final T value = values.get(i);
                        final String valueText = value.toString().toLowerCase();
                        boolean flag = true;
                        // First match against the whole, non-splitted value
                        if (valueText.startsWith(prefixString)) {
                            newValues.add(value);
                            flag = false;
                        } else {
                            final String[] words = valueText.split(" ");
                            final int wordCount = words.length;
    
                            // Start at index 0, in case valueText starts with space(s)
                            for (int k = 0; k < wordCount; k++) {
                                if (words[k].startsWith(prefixString)) {
                                    newValues.add(value);
                                    flag = false;
                                    break;
                                } 
                            }
                        }
    
                        if(flag) {
                            if(approxMatch(valueText, prefixString) <= 3) { //change the stuff and do a levi work
                                approxValues.add(value);
                            }
                            else {
                                final String[] words = valueText.split(" ");
                                final int wordCount = words.length;
    
                                // Start at index 0, in case valueText starts with space(s)
                                for (int k = 0; k < wordCount; k++) {
                                    if(approxMatch(words[k], prefixString) <= 3) {
                                        //leve work
                                        secondApproxValues.add(value);
                                        break;
                                    }
                                }
                            }
                        }
                    }
                    newValues.addAll(approxValues);
                    newValues.addAll(secondApproxValues);
                    results.values = newValues;
                    results.count = newValues.size();
                }
                return results;
            }
            @Override
            protected void publishResults(CharSequence constraint, FilterResults results) {
                //noinspection unchecked
                mObjects = (List<T>) results.values;
                notifyDataSetChanged();
                clear();
                for(T tmp : mObjects){
                    add(tmp);
                }
    
                notifyDataSetChanged();
            }
        }
    
        private int approxMatch (String s, String t) {
              // an approxmimate string matching algo
              return p;
        }
    }
    

    Now in getView method of adapter, you need to refer to mObjects object to get recent available values for ListView

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