Create android photo gallery

I would like to be able to develop an activity that accesses a folder with photos and creates a gallery to view them. I think I have practically everything done, but for whatever reason it does not finish visualizing itself well.

Layout :

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.oftecnica2.agendajose.GaleriaFotos"
    android:orientation="vertical">

    <Gallery
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:id="@+id/galeria" />

    <ImageView
        android:id="@+id/imagengaleria"
        android:layout_width="133dp"
        android:layout_height="194dp"
        android:layout_gravity="center_horizontal"
        android:background="#cfcfcf"
        android:paddingTop="5dp"
        android:paddingBottom="5dp"
        android:paddingLeft="10dp"
        android:paddingRight="10dp"/>

</LinearLayout>

java class :

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.BaseAdapter;
import android.widget.Gallery;
import android.widget.ImageView;

import java.io.File;

public class GaleriaFotos extends AppCompatActivity {

    File[]fotos=null;
    String id="";
    Gallery galeria;
    ImageView imagengaleria;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_galeria_fotos);
        id=getIntent().getExtras().getString("id");
        imagengaleria=(ImageView)findViewById(R.id.imagengaleria);

        cargoLista();

        galeria.setAdapter(new ImageAdapter(this));
        galeria.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {

                ImageView imagengaleria=(ImageView)findViewById(R.id.imagengaleria);
                Bitmap foto = BitmapFactory.decodeFile(fotos[i].getAbsolutePath());
                imagengaleria.setImageBitmap(foto);

            }
        });
    }

    public void cargoLista(){
        try{
            File fichero=new File(Environment.getExternalStorageDirectory().getAbsolutePath()+File.separator+"Reuniones"+File.separator+String.valueOf(id)+File.separator+"fotos");
            fotos=fichero.listFiles();
            galeria=(Gallery)findViewById(R.id.galeria);
            System.out.println("XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX");
            for (File f:fotos){
                System.out.println(f.getAbsolutePath());
            }
        }catch (Exception e){
            System.out.println("NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO");
        }
    }

    private class ImageAdapter extends BaseAdapter {
        private Context context;
        private int itemBackground;
        public ImageAdapter(Context c)
        {
            context = c;
            // sets a grey background; wraps around the images
            TypedArray a =obtainStyledAttributes(R.styleable.MyGallery);
            itemBackground = a.getResourceId(R.styleable.MyGallery_android_galleryItemBackground, 0);
            a.recycle();
        }
        // returns the number of images
        public int getCount() {
            return fotos.length;
        }
        // returns the ID of an item
        public Object getItem(int position) {
            return position;
        }
        // returns the ID of an item
        public long getItemId(int position) {
            return position;
        }
        // returns an ImageView view
        public View getView(int position, View convertView, ViewGroup parent) {
            ImageView imageView = new ImageView(context);
            Bitmap bitmap = BitmapFactory.decodeFile(fotos[position].getAbsolutePath());
            imageView.setImageBitmap(bitmap);
            imageView.setLayoutParams(new Gallery.LayoutParams(100, 100));
            imageView.setBackgroundResource(itemBackground);
            return imageView;
        }
    }
}

As you can see, I pass a number by parameter that is the folder where the photos are.

When executing it, it sometimes gives the typical error of outofmemory and other absolutely nothing appears. Does anyone see the errors?