android - how to highlight the selected Item of Recycler View?

Question

I have a Recycler View with the Images loaded from the Internal Storage. I want to Highlight the selected item when clicked. I tried a lot of thing but it was not working. Actually what I need is when I click any item in Recycler View that Item must go in My ArrayList and it should also get highlighted and again when I click or say unselect it must again become normal. Here is my Code:

public class Images extends Fragment {
    private List<ImageHolder> imageList;
    Cursor imageCursor;

    RecyclerView recyclerView;
    MyImageAdapter adapter;
    ActionButton clickButton;
    List<String> listofImages;
    List<Integer> pos;
    int columnIndex;
    StringBuilder stringBuilder;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,   Bundle savedInstanceState) {
        View rootlayout = inflater.inflate(R.layout.image, container, false);
        listofImages=new ArrayList<String>();
        pos=new ArrayList<Integer>();
        stringBuilder=new StringBuilder();
        ContentResolver imageResolver = getActivity().getContentResolver();
        Uri imageUri = android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI;
        String projection[]={MediaStore.Images.Thumbnails._ID,MediaStore.Images.Media.TITLE};
        imageCursor = getActivity().managedQuery(imageUri, projection, null, null, null);

        clickButton= (ActionButton) rootlayout.findViewById(R.id.action_button);

        recyclerView = (RecyclerView) rootlayout.findViewById(R.id.recycler_view_image);
        adapter = new MyImageAdapter(getActivity(), getImageList());

        recyclerView.setAdapter(adapter);
        recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));

        recyclerView.addOnItemTouchListener(new RecyclerTouchListener(getActivity(),recyclerView,new RecyclerTouchListener.ClickListener() {
            @Override
            public void onClick(View view, int position) {
               TextView tv= (TextView) view.findViewById(R.id.list_text_all);
                    int flag=0;

                    String[] projection = {MediaStore.Images.Media.DATA};
                    imageCursor = getActivity().managedQuery(MediaStore.Images.Media.EXTERNAL_CONTENT_URI,
                            projection, 
                            null,       
                            null,
                            null);
                    columnIndex = imageCursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA);
                    imageCursor.moveToPosition(position);
                    // Get image filename
                    String imagePath = imageCursor.getString(columnIndex);
                    if (listofImages.contains(imagePath)){
                        Log.d("Contains Test","Yes");
                        listofImages.remove(imagePath);
                        pos.remove(position);
                    } else {
                        listofImages.add(imagePath);
                        pos.add(position);
                        Log.d("Contains Test","No");
                    }

                String s=listofImages.size()+" "+imagePath;
                Log.d("Inserted",s);
            }

            @Override
            public void onLongClick(View view, int position) {}
        }));

        clickButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                for (int i=0;i<listofImages.size();i++){
                    stringBuilder.append(listofImages.get(i)+"
");
                }
                Toast.makeText(getActivity(),stringBuilder,Toast.LENGTH_LONG).show();
            }
        });

        return rootlayout;
    }

    public List<ImageHolder> getImageList() {
        imageList=new ArrayList<ImageHolder>();

        if(imageCursor!=null && imageCursor.moveToFirst()){

           int titleColumn = imageCursor.getColumnIndex
                    (android.provider.MediaStore.Images.Media.TITLE);
            int idColumn = imageCursor.getColumnIndex
                    (android.provider.MediaStore.Images.Media._ID);

            do {
                ImageHolder img=new ImageHolder();
                img.id=imageCursor.getLong(idColumn);
                img.title=imageCursor.getString(titleColumn);

                img.iconid= imageCursor.getInt(idColumn);


                imageList.add(img);
            }
            while (imageCursor.moveToNext());
        }

        return  imageList;
    }
}

This is my Adapter Class:

public class MyImageAdapter extends RecyclerView.Adapter<MyImageAdapter.MyViewHolder> {
    Context context;
    private LayoutInflater inflater;
    List<ImageHolder> data= Collections.emptyList();
    private ClickListener clickListener;
    int width,height;

    public MyImageAdapter(Context context, List<ImageHolder> data1) {
        inflater = LayoutInflater.from(context);
        this.data=data1;
        this.context=context;
    }

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = inflater.inflate(R.layout.all_row, parent, false);
        MyViewHolder holder=new MyViewHolder(view);
        return holder;
    }

    @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {
        try{
            ImageHolder current=data.get(position);
            holder.title.setText(current.title);

            Log.d("Imageid:"+current.iconid,"");
            Uri IMAGE_URI = Uri.withAppendedPath(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, "" + current.iconid);

            Bitmap bitmap = Bitmap.createScaledBitmap(decodeUri(IMAGE_URI), 200, 200, true);
            holder.img.setImageBitmap(bitmap);
        }
        catch(Exception e){}
    }
    public void deleteRecyclerData(int position){
        data.remove(position);
        notifyItemRemoved(position);
    }


    private Bitmap decodeUri(Uri selectedImage) throws FileNotFoundException {
        BitmapFactory.Options o = new BitmapFactory.Options();
        o.inJustDecodeBounds = true;
        BitmapFactory.decodeStream(
               context.getContentResolver().openInputStream(selectedImage), null, o);

        final int REQUIRED_SIZE = 100;

        int width_tmp = o.outWidth, height_tmp = o.outHeight;
        int scale = 1;
        while (true) {
            if (width_tmp / 2 < REQUIRED_SIZE || height_tmp / 2 < REQUIRED_SIZE) {
                break;
            }
            width_tmp /= 2;
            height_tmp /= 2;
            scale *= 2;
        }

        BitmapFactory.Options o2 = new BitmapFactory.Options();
        o2.inSampleSize = scale;
        return BitmapFactory.decodeStream(
                context.getContentResolver().openInputStream(selectedImage), null, o2);
    }
    @Override
    public int getItemCount() {
        return data.size();
    }

    public class MyViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener{
        TextView title;
      // TextView artist;
        ImageView img;
        CheckBox checkBox;

        public MyViewHolder(View itemView) {
            super(itemView);
            title= (TextView) itemView.findViewById(R.id.list_text_all);
            img= (ImageView) itemView.findViewById(R.id.list_image_all);
            img.setOnClickListener(this);
        }

        @Override
        public void onClick(View v) {}
    }
    public interface ClickListener{
        public void itemClicked(View view, int position);
    }
}

Answer 1

You can use a StateListDrawable to achieve the desired effect.

Example

Create a new Drawable resource file in your drawable directory with the following content:

selector_row.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <!-- Color when the row is selected -->
    <item android:drawable="@android:color/darker_gray" android:state_pressed="false" android:state_selected="true" />
    <!-- Standard background color -->
    <item android:drawable="@android:color/white" android:state_selected="false" />
</selector>

Now simply use this StateListDrawable as the background in the row-layout of your RecyclerView

row_recyclerview.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@drawable/selector_row">

    <!-- row content -->

</RelativeLayout>

Now as soon as the onClick() method in your adapter is called you simply need to do the following:

// myBackground is the RelativeLayout root of your row
myBackground.setSelected(true);

The rows' background will have the color (in this case darker_gray) as long as you call myBackground.setSelected(false). Of course you should create a SparseBooleanArray for example in order to know which row is selected and which isn't since the rows will be reused when scrolling.

Edit: Remember selected items
The idea behind the SparseBooleanArray is to remember the items which are selected. Following a sample on how to use it:

public class MyImageAdapter extends RecyclerView.Adapter<MyImageAdapter.MyViewHolder> {

    private SparseBooleanArray selectedItems;

    // Other stuff [...]

    @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {
        // Set the selected state of the row depending on the position
        holder.myBackground.setSelected(selectedItems.get(position, false));
    }

    public class MyViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener{

        @Override
        public void onClick(View v) {
              // Save the selected positions to the SparseBooleanArray 
              if (selectedItems.get(getAdapterPosition(), false)) {
                  selectedItems.delete(getAdapterPosition());
                  myBackground.setSelected(false);
              }
              else {
                  selectedItems.put(getAdapterPosition(), true);
                  myBackground.setSelected(true);
              }
        }
    }
}