Re-arrange ArrayList elements

Question

I have n number of list of items, containing name and position. If I delete a row from list, I want to re-arrange the positions of the list.

For example:

Vijay  01
Dhas   02
Arun   03
prabhu 04

If I delete Dhas from the list, Arun's position should be 02 and prabhu's position should be 03.

My model class is

public class Model {

    private String name;
    private int position;

    public Model(String name, int position) {
        this.name = name;
        this.position = position;

    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getPosition() {
        return position;
    }

    public void setPosition(int position) {
        this.position = position;
    }

}

I tried the following:

 @Override
        public void onBindViewHolder(final MyViewHolder holder, final int position) {
            holder.imvDelete.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {

                    int tempPreviousValue;
                    for(int i = position ; i < mData.size()-1 ; i++){
                        int deletedPosition = mData.get(i).getPosition();
                        tempPreviousValue = mData.get(position+1).getPosition();
                        mData.get(position+1).setPosition(deletedPosition);
                    }
                    mData.remove(position);
                    notifyDataSetChanged();


                }
            }); 
        }

But I am not getting the correct order. Can anyone give some ideas to re-arrange the array?

Answer 1

I actually recommend just using a plain list of names, and then relying on List#indexOf to find the positions.

String[] names = new String[] { "Vijay", "Dhas", "Arun", "prabhu" };
List<String> list = Arrays.asList(names);
list.remove("Dhas");
System.out.println(list.indexOf("Arun"));  // should be 1, was 2 before deletion

You may also use List<Model>, and the same logic applies. I am advocating that you let the list API maintain the position number for you, which it already does.

Answer 2

Just make an loop, and use increment index as new position like this

    mData.remove(position);
    for (int i = 0; i < mData.size(); i++) {
        mData.get(i).setPosition(i);
    }
    notifyDataSetChanged();

Or if your position in model starts from numer 1, use .setPosition(i+1).
One thing, don't use position in recyclerview adapter, because this may have a wrong number, use holder.getAdapterPosition(); instead.

Answer 3

Maybe something like this:

int positionToDelete = 2;
Model modelToDelete = modelList.get(positionToDelete - 1);
modelList.remove(modelToDelete);
for(int i = positionToDelete - 1; i < modelList.size(); i++){
  Model modelToChange = modelList.get(i);
  modelToChange.setPosition(modelToChange.getPosition() - 1);
}

The list will be this before deleting:

[{name = Vijay, position = 1},
 {name = Dhas, position = 2},
 {name = Arun, position = 3},
 {name = prabhu, position = 4}]

And this after deleting:

[{name = Vijay, position = 1},
 {name = Arun, position = 2},
 {name = prabhu, position = 3}]

Try it online.

Or if you already know the Model you want to delete, the first two lines are this instead:

Model modelToDelete = ...; // Model retrieved from some place
int positionToDelete = modelToDelete.getPosition();

The rest stays the same.

Answer 4

you just need to refresh Adapter with notifyDataSetChanged(); and write code like that :-

@Override
        public void onBindViewHolder(final MyViewHolder holder, final int position) {
            mData.get(position).setPosition(position);
        }

also add one more method for remove item in adapter.

public void remove_item(int position) {
       mData.remove(position);
        notifyDataSetChanged();
    }

Answer 5

       @Override
        public void onBindViewHolder(final MyViewHolder holder, final int position) {
            holder.imvDelete.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    for (int i=mData.size()-1;i>position;i--){
                        mData.get(i).setPosition(mData.get(i-1).getPosition());
                    }
                    mData.remove(position);
                    notifyDataSetChanged();
                }
            });
        }

Answer 6

Create a method something like this

public void removeItem(int position){
    // just a safe check
    if(position >= getItemCount() ){
        return;
    }

    mData.remove(position);
    notifyItemRemoved(position);
}

then call and pass the position you wanted to be removed.

Answer 7

Here's one using Java8 streams:

List<String> l2 = list.stream().filter(a -> !a.equals("Dhas")).collect(Collectors.toList());

Note that this would create a new list.