How to center ImageView?

I have a RecyclerAdapter in which several images are horizontally placed. How to center each ImageView in item_custom

ListAdapter.java

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

import androidx.recyclerview.widget.RecyclerView;

import com.example.geometry.R;

import java.util.List;

public class ListAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

    private List<ItemAdapter> mList;
    private Context mContext;
    public ListAdapter(List<ItemAdapter> list, Context context){
        super();
        mList = list;
        mContext = context;
    }
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int i) {
        View v = LayoutInflater.from(mContext).inflate(R.layout.item_custom, parent, false);

        final ViewHolder viewHolder = new ViewHolder(v);

        viewHolder.mImg.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Toast.makeText(v.getContext(), "Input mode = " + viewHolder.getAdapterPosition(), Toast.LENGTH_SHORT).show();
                Builder.mode = viewHolder.getAdapterPosition();
            }
        });

        return viewHolder;
    }

    @Override
    public void onBindViewHolder( RecyclerView.ViewHolder viewHolder, int position) {
        ItemAdapter itemAdapter = mList.get(position);
        ((ViewHolder) viewHolder).mImg.setImageResource(itemAdapter.getImage());
    }

    @Override
    public int getItemCount() {
        return mList.size();
    }

    class ViewHolder extends RecyclerView.ViewHolder{

        public TextView mTv_name;
        public ImageView mImg;
        public ViewHolder(View itemView) {

            super(itemView);
            mImg = (ImageView) itemView.findViewById(R.id.img_item);

        }
    }
}

ItemAdapter.java

public class ItemAdapter {
    private int image;

    public int getImage() {
        return image;
    }

    public void setImage(int image) {
        this.image = image;
    }
}

MainActivity.java

import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
import android.widget.ImageButton;
import android.widget.ListView;
import android.widget.RelativeLayout;

import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import com.example.geometry.GUI.Builder;
import com.example.geometry.GUI.ItemAdapter;
import com.example.geometry.GUI.ListAdapter;
import com.example.geometry.Output.SolveActivity;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private RecyclerView mRecycleView;
    private List<ItemAdapter> mList = new ArrayList<>();
    private ListAdapter mAdapter;
    ListView listView;
    RelativeLayout layout;

    ImageButton solve_button;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        init();
        addList();
        adapter();
    }

    private void init(){
        setContentView(R.layout.activity_main);
        layout = new RelativeLayout(this);
        mRecycleView = findViewById(R.id.recycler_view);//new RecyclerView(this);

        RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.WRAP_CONTENT,
                RelativeLayout.LayoutParams.WRAP_CONTENT);
        params.addRule(RelativeLayout.ALIGN_PARENT_BOTTOM);
        mRecycleView.setLayoutParams(params);
    }
    private void addList(){
        ItemAdapter itemAdapter = new ItemAdapter();
        itemAdapter.setImage(R.drawable.circle);
        mList.add(itemAdapter);

        itemAdapter = new ItemAdapter();
        itemAdapter.setImage(R.drawable.line);
        mList.add(itemAdapter);

        itemAdapter = new ItemAdapter();
        itemAdapter.setImage(R.drawable.move);
        mList.add(itemAdapter);

        itemAdapter = new ItemAdapter();
        itemAdapter.setImage(R.drawable.angle);
        mList.add(itemAdapter);

        itemAdapter = new ItemAdapter();
        itemAdapter.setImage(R.drawable.regular_triangle);
        mList.add(itemAdapter);

        itemAdapter = new ItemAdapter();
        itemAdapter.setImage(R.drawable.right_triangle);
        mList.add(itemAdapter);

        itemAdapter = new ItemAdapter();
        itemAdapter.setImage(R.drawable.square);
        mList.add(itemAdapter);

        itemAdapter = new ItemAdapter();
        itemAdapter.setImage(R.drawable.trapeze);
        mList.add(itemAdapter);
    }

    private void adapter(){
        mAdapter = new ListAdapter(mList, this);
        mRecycleView.setAdapter(mAdapter);
        mRecycleView.setLayoutManager(new LinearLayoutManager(this, RecyclerView.HORIZONTAL, false));
        mAdapter.notifyDataSetChanged();

    }


}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ImageButton
        android:id="@+id/solve_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:layout_margin="30dp"
        android:background="@drawable/ic_calculator" />

    <com.example.geometry.GUI.Builder
        android:id="@+id/builder"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_above="@+id/recycler_view"
        />

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
    />

    <EditText
        android:id="@+id/editText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="10"
        android:inputType="textPersonName"
        android:text="Name" />

</RelativeLayout>

item_custom.java

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_margin="2dp"
    android:background="#fff"
    android:layout_height="wrap_content">
    android:layout_gravity="center"
    android:scaleType="center">
    <ImageView
        android:id="@+id/img_item"
        android:layout_width="wrap_content"
        android:contentDescription="@string/app_name"
        android:layout_height="wrap_content" 
        android:layout_gravity="center"
        android:scaleType="center"
        android:layout_centerInParent="true"/>


</RelativeLayout>

Change your item_custom according to my code

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_margin="2dp"
    android:background="#fff">

    <ImageView
        android:id="@+id/img_item"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:layout_gravity="center"
        android:src="@drawable/ic_search"
        android:contentDescription="@string/app_name"
        android:scaleType="center" />


</RelativeLayout>

Hope it will work definately tested by myself

Happy coding! Thankew!