How to select multiple images from gallery in android?

There is EXTRA_ALLOW_MULTIPLE option is set on the intent through the Intent.putExtra() method:

  intent.putExtra(Intent.EXTRA_ALLOW_MULTIPLE, true);

In your code write as below:

Intent intent = new Intent();
intent.setType("image/*");
intent.putExtra(Intent.EXTRA_ALLOW_MULTIPLE, true);
intent.setAction(Intent.ACTION_GET_CONTENT);
startActivityForResult(Intent.createChooser(intent,"Select Picture"), RESULT_LOAD_IMAGE1);

Note: the EXTRA_ALLOW_MULTIPLE option is only available in Android API 18 and higher.

If you want to develop your own gallery then check out the Select Multiple Images from Gallery

Use below library for multiple image selection from gallary. https://github.com/sangcomz/FishBun

Implement custom gallery selector with below code :

activity_main

<ScrollView
    android:layout_width="match_parent"
    android:layout_height="wrap_content" android:id="@+id/scroll1"
    >

    <LinearLayout
        android:id="@+id/lnrImages"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">

    </LinearLayout>
</ScrollView>

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:id="@+id/linearLayout">
    <Button
        android:id="@+id/btnAddPhots"
        android:layout_width="0dp"
        android:layout_weight="1"
        android:layout_height="wrap_content"
        android:text="Add Phots"/>

    <Button
        android:id="@+id/btnSaveImages"
        android:layout_width="0dp"
        android:layout_weight="1"
        android:layout_height="wrap_content"
        android:text="Save"/>
</LinearLayout>

custom_gallery

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:orientation="vertical">
    <GridView
        android:id="@+id/grdImages"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:numColumns="auto_fit"
        android:verticalSpacing="10dp"
        android:horizontalSpacing="10dp"
        android:columnWidth="90dp"
        android:stretchMode="columnWidth"
        android:gravity="center"/>

    <Button
        android:id="@+id/btnSelect"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Select"
        android:layout_marginTop="5dp"/>

</LinearLayout>

custom_gallery_item

    <ImageView
        android:id="@+id/imgThumb"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

    <CheckBox
        android:id="@+id/chkImage"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="top|right"/>
</FrameLayout>

MainActivity

public class MainActivity extends Activity implements View.OnClickListener{

    private LinearLayout lnrImages;
    private Button btnAddPhots;
    private Button btnSaveImages;
    private ArrayList<String> imagesPathList;
    private Bitmap yourbitmap;
    private Bitmap resized;
    private final int PICK_IMAGE_MULTIPLE =1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        lnrImages = (LinearLayout)findViewById(R.id.lnrImages);
        btnAddPhots = (Button)findViewById(R.id.btnAddPhots);
        btnSaveImages = (Button)findViewById(R.id.btnSaveImages);
        btnAddPhots.setOnClickListener(this);
        btnSaveImages.setOnClickListener(this);
    }
    @Override
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.btnAddPhots:
                Intent intent = new Intent(MainActivity.this,CustomPhotoGalleryActivity.class);
                startActivityForResult(intent,PICK_IMAGE_MULTIPLE);
                break;
            case R.id.btnSaveImages:
                if(imagesPathList !=null){
                    if(imagesPathList.size()>1) {
                        Toast.makeText(MainActivity.this, imagesPathList.size() + " no of images are selected", Toast.LENGTH_SHORT).show();
                    }else{
                        Toast.makeText(MainActivity.this, imagesPathList.size() + " no of image are selected", Toast.LENGTH_SHORT).show();
                    }
                }else{
                    Toast.makeText(MainActivity.this," no images are selected", Toast.LENGTH_SHORT).show();
                }
                break;
        }
    }
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (resultCode == RESULT_OK) {
            if(requestCode == PICK_IMAGE_MULTIPLE){
                imagesPathList = new ArrayList<String>();
                String[] imagesPath = data.getStringExtra("data").split("\\|");
                try{
                    lnrImages.removeAllViews();
                }catch (Throwable e){
                    e.printStackTrace();
                }
                for (int i=0;i<imagesPath.length;i++){
                    imagesPathList.add(imagesPath[i]);
                    yourbitmap = BitmapFactory.decodeFile(imagesPath[i]);
                    ImageView imageView = new ImageView(this);
                    imageView.setImageBitmap(yourbitmap);
                    imageView.setAdjustViewBounds(true);
                    lnrImages.addView(imageView);
                }
            }
        }

    }

}

CustomPhotoGalleryActivity

 public class CustomPhotoGalleryActivity extends Activity {

    private GridView grdImages;
    private Button btnSelect;

    private ImageAdapter imageAdapter;
    private String[] arrPath;
    private boolean[] thumbnailsselection;
    private int ids[];
    private int count;


    /**
     * Overrides methods
     */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.custom_gallery);
        grdImages= (GridView) findViewById(R.id.grdImages);
        btnSelect= (Button) findViewById(R.id.btnSelect);

        final String[] columns = { MediaStore.Images.Media.DATA, MediaStore.Images.Media._ID };
        final String orderBy = MediaStore.Images.Media._ID;
        @SuppressWarnings("deprecation")
        Cursor imagecursor = managedQuery(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, columns, null, null, orderBy);
        int image_column_index = imagecursor.getColumnIndex(MediaStore.Images.Media._ID);
        this.count = imagecursor.getCount();
        this.arrPath = new String[this.count];
        ids = new int[count];
        this.thumbnailsselection = new boolean[this.count];
        for (int i = 0; i < this.count; i++) {
            imagecursor.moveToPosition(i);
            ids[i] = imagecursor.getInt(image_column_index);
            int dataColumnIndex = imagecursor.getColumnIndex(MediaStore.Images.Media.DATA);
            arrPath[i] = imagecursor.getString(dataColumnIndex);
        }

        imageAdapter = new ImageAdapter();
        grdImages.setAdapter(imageAdapter);
        imagecursor.close();


        btnSelect.setOnClickListener(new OnClickListener() {

            public void onClick(View v) {
                final int len = thumbnailsselection.length;
                int cnt = 0;
                String selectImages = "";
                for (int i = 0; i < len; i++) {
                    if (thumbnailsselection[i]) {
                        cnt++;
                        selectImages = selectImages + arrPath[i] + "|";
                    }
                }
                if (cnt == 0) {
                    Toast.makeText(getApplicationContext(), "Please select at least one image", Toast.LENGTH_LONG).show();
                } else {

                    Log.d("SelectedImages", selectImages);
                    Intent i = new Intent();
                    i.putExtra("data", selectImages);
                    setResult(Activity.RESULT_OK, i);
                    finish();
                }
            }
        });
    }
    @Override
    public void onBackPressed() {
        setResult(Activity.RESULT_CANCELED);
        super.onBackPressed();

    }

    /**
     * Class method
     */

    /**
     * This method used to set bitmap.
     * @param iv represented ImageView 
     * @param id represented id
     */

    private void setBitmap(final ImageView iv, final int id) {

        new AsyncTask<Void, Void, Bitmap>() {

            @Override
            protected Bitmap doInBackground(Void... params) {
                return MediaStore.Images.Thumbnails.getThumbnail(getApplicationContext().getContentResolver(), id, MediaStore.Images.Thumbnails.MICRO_KIND, null);
            }

            @Override
            protected void onPostExecute(Bitmap result) {
                super.onPostExecute(result);
                iv.setImageBitmap(result);
            }
        }.execute();
    }


    /**
     * List adapter
     * @author tasol
     */

    public class ImageAdapter extends BaseAdapter {
        private LayoutInflater mInflater;

        public ImageAdapter() {
            mInflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        }

        public int getCount() {
            return count;
        }

        public Object getItem(int position) {
            return position;
        }

        public long getItemId(int position) {
            return position;
        }

        public View getView(int position, View convertView, ViewGroup parent) {
            final ViewHolder holder;
            if (convertView == null) {
                holder = new ViewHolder();
                convertView = mInflater.inflate(R.layout.custom_gallery_item, null);
                holder.imgThumb = (ImageView) convertView.findViewById(R.id.imgThumb);
                holder.chkImage = (CheckBox) convertView.findViewById(R.id.chkImage);

                convertView.setTag(holder);
            } else {
                holder = (ViewHolder) convertView.getTag();
            }
            holder.chkImage.setId(position);
            holder.imgThumb.setId(position);
            holder.chkImage.setOnClickListener(new OnClickListener() {

                public void onClick(View v) {
                    CheckBox cb = (CheckBox) v;
                    int id = cb.getId();
                    if (thumbnailsselection[id]) {
                        cb.setChecked(false);
                        thumbnailsselection[id] = false;
                    } else {
                        cb.setChecked(true);
                        thumbnailsselection[id] = true;
                    }
                }
            });
            holder.imgThumb.setOnClickListener(new OnClickListener() {

                public void onClick(View v) {
                    int id = holder.chkImage.getId();
                    if (thumbnailsselection[id]) {
                        holder.chkImage.setChecked(false);
                        thumbnailsselection[id] = false;
                    } else {
                        holder.chkImage.setChecked(true);
                        thumbnailsselection[id] = true;
                    }
                }
            });
            try {
                setBitmap(holder.imgThumb, ids[position]);
            } catch (Throwable e) {
            }
            holder.chkImage.setChecked(thumbnailsselection[position]);
            holder.id = position;
            return convertView;
        }
    }


    /**
     * Inner class
     * @author tasol
     */
    class ViewHolder {
        ImageView imgThumb;
        CheckBox chkImage;
        int id;
    }

}

Here is the code for Select Multiple Image and video from Default Gallery.

Button buttonLoadImage = (Button) findViewById(R.id.buttonLoadPicture);
    buttonLoadImage.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View arg0) {

            Intent i = new Intent();
            i.setType("image/*");
       //i.setType("video/*");
            i.putExtra(Intent.EXTRA_ALLOW_MULTIPLE, true);
            i.setAction(Intent.ACTION_GET_CONTENT);
            startActivityForResult(
                    Intent.createChooser(i, "android.intent.action.SEND_MULTIPLE"), 1);
        }
    });

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);

    System.out.println("++data" + data.getClipData().getItemCount());// Get count of image here.

        System.out.println("++count" + data.getClipData().getItemCount());
        Uri selectedImage = data.getClipData().getItemAt(0).getUri();//As of now use static position 0 use as per itemcount.
        Bitmap bitmap = null;
  //        Uri selectedImage1 = data.getData();
        try {
            bitmap = MediaStore.Images.Media.getBitmap(this.getContentResolver(), selectedImage);
        } catch (IOException e) {
            e.printStackTrace();
        }
        System.out.println("+++ clipdate" + selectedImage);

        ImageView imageView = (ImageView) findViewById(R.id.imgView);
        imageView.setImageBitmap(bitmap);
    //        }

}