<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:orientation="vertical"
    tools:context="[removed for stackOverflow bc included full name]">

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/btn"
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="40dp"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Add Image" />

    <android.support.v7.widget.RecyclerView
        android:id="@+id/galleryRecyclerView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true" />
</LinearLayout>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content" android:layout_height="wrap_content">
    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="1dp"
        android:id="@+id/imageGalleryView"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true"
        />
</RelativeLayout>

public class MainActivity extends AppCompatActivity {

    private Button btn;
    private ImageView imageview;
    private static final String IMAGE_DIRECTORY = "/BingoAppGallery";
    private int GALLERY = 1, CAMERA = 2;



    private String mImageFileLocation = "";
    private String galleryLocation = "Bingo Gallery";
    private File BingoGalleryFolder;
    private RecyclerView recycleView;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        /******/

        createImageGallery();
        recycleView = (RecyclerView) findViewById(R.id.galleryRecyclerView);
        GridLayoutManager layoutManager = new GridLayoutManager(this,2);
        recycleView.setLayoutManager(layoutManager);
        RecyclerView.Adapter imageAdapter = new ImageAdapter(BingoGalleryFolder);
        recycleView.setAdapter(imageAdapter);



        btn = (Button) findViewById(R.id.btn);
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                showPictureDialog();
            }
        });

    }


    private void showPictureDialog(){
        AlertDialog.Builder pictureDialog = new AlertDialog.Builder(this);
        pictureDialog.setTitle("Select Action");
        String[] pictureDialogItems = {
                "Select photo from gallery",
                "Capture photo from camera" };
        pictureDialog.setItems(pictureDialogItems,
                new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        switch (which) {
                            case 0:
                                choosePhotoFromGallary();
                                break;
                            case 1:
                                takePhotoFromCamera();
                                break;
                        }
                    }
                });
        pictureDialog.show();
    }

    public void choosePhotoFromGallary() {
        Intent galleryIntent = new Intent(Intent.ACTION_PICK,
                android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI);

        startActivityForResult(galleryIntent, GALLERY);
    }

    private void takePhotoFromCamera() {
        Intent intent = new Intent(android.provider.MediaStore.ACTION_IMAGE_CAPTURE);
        startActivityForResult(intent, CAMERA);
    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {

        super.onActivityResult(requestCode, resultCode, data);
        if (resultCode == this.RESULT_CANCELED) {
            return;
        }
        if (requestCode == GALLERY) {
            if (data != null) {
                Uri contentURI = data.getData();
                try {
                    Bitmap bitmap = MediaStore.Images.Media.getBitmap(this.getContentResolver(), contentURI);
                    String path = saveImage(bitmap);
                    Toast.makeText(MainActivity.this, "Image Saved!", Toast.LENGTH_SHORT).show();


                } catch (IOException e) {
                    e.printStackTrace();
                    Toast.makeText(MainActivity.this, "Failed!", Toast.LENGTH_SHORT).show();
                }
            }

        } else if (requestCode == CAMERA) {
            Bitmap thumbnail = (Bitmap) data.getExtras().get("data");
            saveImage(thumbnail);
            Toast.makeText(MainActivity.this, "Image Saved!", Toast.LENGTH_SHORT).show();
        }
        RecyclerView.Adapter newImageAdapter = new ImageAdapter(BingoGalleryFolder); //***************//
        recycleView.swapAdapter(newImageAdapter,false);
    }

    public String saveImage(Bitmap myBitmap) {
        ByteArrayOutputStream bytes = new ByteArrayOutputStream();
        myBitmap.compress(Bitmap.CompressFormat.JPEG, 90, bytes);
        File wallpaperDirectory = new File(
                Environment.getExternalStorageDirectory() + IMAGE_DIRECTORY);
        // have the object build the directory structure, if needed.
        if (!wallpaperDirectory.exists()) {
            wallpaperDirectory.mkdirs();
        }

        try {
            File f = new File(wallpaperDirectory, Calendar.getInstance()
                    .getTimeInMillis() + ".jpg");
            f.createNewFile();
            FileOutputStream fo = new FileOutputStream(f);
            fo.write(bytes.toByteArray());
            MediaScannerConnection.scanFile(this,
                    new String[]{f.getPath()},
                    new String[]{"image/jpeg"}, null);
            fo.close();
            Log.d("TAG", "File Saved::--->" + f.getAbsolutePath());

            return f.getAbsolutePath();
        } catch (IOException e1) {
            e1.printStackTrace();
        }
        return "";
    }



    private void createImageGallery()
    {
        File storageDirectory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES);
        BingoGalleryFolder = new File(storageDirectory,galleryLocation);
        if(!BingoGalleryFolder.exists())
            BingoGalleryFolder.mkdirs();

    }

public class ImageAdapter extends RecyclerView.Adapter<ImageAdapter.ViewHolder>
{
    private File imagesFile;

    public ImageAdapter(File folderFile)
    {
        imagesFile = folderFile;
    }
    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType)
    {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.gallery_images_relative_layout,parent,false);
        return new ViewHolder(view);
    }
    @Override
    public void onBindViewHolder(ViewHolder holder, int position)
    {
        File imageFile =imagesFile.listFiles()[position];
        Bitmap imageBitmap = BitmapFactory.decodeFile(imageFile.getAbsolutePath());
        holder.getImageView().setImageBitmap(imageBitmap);


    }
    @Override
    public int getItemCount()
    {
        return imagesFile.listFiles().length;
    }

    public static class ViewHolder extends RecyclerView.ViewHolder
    {
        private ImageView imageView;

        public ViewHolder(View view)
        {
            super(view);
            imageView = (ImageView) view.findViewById(R.id.imageGalleryView);

        }
        public ImageView getImageView()
        {
            return imageView;
        }
    }
}