Get all images from gallery in android programmatically 
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gallery2

activity_main.xml
<RelativeLayout android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#ffffff"
    xmlns:android="http://schemas.android.com/apk/res/android">
    

    <GridView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/gv_folder"
        android:numColumns="2"
        android:layout_marginLeft="10dp"
        android:layout_marginRight="10dp"></GridView>

    
</RelativeLayout>
MainActivity.java
package galleryimages.galleryimages;

import android.Manifest;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.database.Cursor;
import android.net.Uri;
import android.provider.MediaStore;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.GridView;
import android.widget.Toast;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {
    public static ArrayList<Model_images> al_images = new ArrayList<>();
    boolean boolean_folder;
    Adapter_PhotosFolder obj_adapter;
    GridView gv_folder;
    private static final int REQUEST_PERMISSIONS = 100;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        gv_folder = (GridView)findViewById(R.id.gv_folder);

        gv_folder.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
                Intent intent = new Intent(getApplicationContext(), PhotosActivity.class);
                intent.putExtra("value",i);
                startActivity(intent);
            }
        });


        if ((ContextCompat.checkSelfPermission(getApplicationContext(),
                Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) && (ContextCompat.checkSelfPermission(getApplicationContext(),
                Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED)) {
            if ((ActivityCompat.shouldShowRequestPermissionRationale(MainActivity.this,
                    Manifest.permission.WRITE_EXTERNAL_STORAGE)) && (ActivityCompat.shouldShowRequestPermissionRationale(MainActivity.this,
                    Manifest.permission.READ_EXTERNAL_STORAGE))) {

            } else {
                ActivityCompat.requestPermissions(MainActivity.this,
                        new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE, Manifest.permission.READ_EXTERNAL_STORAGE},
                        REQUEST_PERMISSIONS);
            }
        }else {
            Log.e("Else","Else");
            fn_imagespath();
        }



    }

    public ArrayList<Model_images> fn_imagespath() {
        al_images.clear();

        int int_position = 0;
        Uri uri;
        Cursor cursor;
        int column_index_data, column_index_folder_name;

        String absolutePathOfImage = null;
        uri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI;

        String[] projection = {MediaStore.MediaColumns.DATA, MediaStore.Images.Media.BUCKET_DISPLAY_NAME};

        final String orderBy = MediaStore.Images.Media.DATE_TAKEN;
        cursor = getApplicationContext().getContentResolver().query(uri, projection, null, null, orderBy + " DESC");

        column_index_data = cursor.getColumnIndexOrThrow(MediaStore.MediaColumns.DATA);
        column_index_folder_name = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.BUCKET_DISPLAY_NAME);
        while (cursor.moveToNext()) {
            absolutePathOfImage = cursor.getString(column_index_data);
            Log.e("Column", absolutePathOfImage);
            Log.e("Folder", cursor.getString(column_index_folder_name));

            for (int i = 0; i < al_images.size(); i++) {
                if (al_images.get(i).getStr_folder().equals(cursor.getString(column_index_folder_name))) {
                    boolean_folder = true;
                    int_position = i;
                    break;
                } else {
                    boolean_folder = false;
                }
            }


            if (boolean_folder) {

                ArrayList<String> al_path = new ArrayList<>();
                al_path.addAll(al_images.get(int_position).getAl_imagepath());
                al_path.add(absolutePathOfImage);
                al_images.get(int_position).setAl_imagepath(al_path);

            } else {
                ArrayList<String> al_path = new ArrayList<>();
                al_path.add(absolutePathOfImage);
                Model_images obj_model = new Model_images();
                obj_model.setStr_folder(cursor.getString(column_index_folder_name));
                obj_model.setAl_imagepath(al_path);

                al_images.add(obj_model);


            }


        }


        for (int i = 0; i < al_images.size(); i++) {
            Log.e("FOLDER", al_images.get(i).getStr_folder());
            for (int j = 0; j < al_images.get(i).getAl_imagepath().size(); j++) {
                Log.e("FILE", al_images.get(i).getAl_imagepath().get(j));
            }
        }
        obj_adapter = new Adapter_PhotosFolder(getApplicationContext(),al_images);
        gv_folder.setAdapter(obj_adapter);
        return al_images;
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);

        switch (requestCode) {
            case REQUEST_PERMISSIONS: {
                for (int i = 0; i < grantResults.length; i++) {
                    if (grantResults.length > 0 && grantResults[i] == PackageManager.PERMISSION_GRANTED) {
                        fn_imagespath();
                    } else {
                        Toast.makeText(MainActivity.this, "The app was not allowed to read or write to your storage. Hence, it cannot function properly. Please consider granting it this permission", Toast.LENGTH_LONG).show();
                    }
                }
            }
        }
    }

}
adapter_photosfolder.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"
    android:orientation="vertical">


    <LinearLayout
        android:layout_width="match_parent"
        android:orientation="vertical"
        android:layout_marginTop="10dp"
        android:layout_marginLeft="10dp"
        android:background="@drawable/drawable_photofolder"
        android:layout_marginRight="10dp"
        android:layout_marginBottom="10dp"
        android:layout_height="match_parent">
    <ImageView
        android:layout_width="150dp"
        android:layout_gravity="center"
        android:layout_height="150dp"
        android:id="@+id/iv_image"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/tv_folder"
        android:textStyle="bold"
        android:textColor="#000000"
        android:layout_marginLeft="10dp"
        android:textSize="15dp"/>

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/tv_folder2"
            android:textColor="#dfdfdf"
            android:layout_marginBottom="10dp"
            android:layout_marginLeft="10dp"
            android:textSize="15dp"/>
    </LinearLayout>

    <RelativeLayout
        android:layout_width="match_parent"
        android:id="@+id/rl_select"
        android:alpha="0.5"
        android:layout_height="match_parent">

    </RelativeLayout>

</RelativeLayout>
Adapter_PhotosFolder.java
package galleryimages.galleryimages;


import android.content.Context;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;

import com.bumptech.glide.Glide;
import com.bumptech.glide.load.engine.DiskCacheStrategy;

import java.util.ArrayList;


public class Adapter_PhotosFolder extends ArrayAdapter<Model_images> {

    Context context;
    ViewHolder viewHolder;
    ArrayList<Model_images> al_menu = new ArrayList<>();


    public Adapter_PhotosFolder(Context context, ArrayList<Model_images> al_menu) {
        super(context, R.layout.adapter_photosfolder, al_menu);
        this.al_menu = al_menu;
        this.context = context;


    }

    @Override
    public int getCount() {

        Log.e("ADAPTER LIST SIZE", al_menu.size() + "");
        return al_menu.size();
    }

    @Override
    public int getItemViewType(int position) {
        return position;
    }

    @Override
    public int getViewTypeCount() {
        if (al_menu.size() > 0) {
            return al_menu.size();
        } else {
            return 1;
        }
    }

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


    @Override
    public View getView(final int position, View convertView, ViewGroup parent) {

        if (convertView == null) {

            viewHolder = new ViewHolder();
            convertView = LayoutInflater.from(getContext()).inflate(R.layout.adapter_photosfolder, parent, false);
            viewHolder.tv_foldern = (TextView) convertView.findViewById(R.id.tv_folder);
            viewHolder.tv_foldersize = (TextView) convertView.findViewById(R.id.tv_folder2);
            viewHolder.iv_image = (ImageView) convertView.findViewById(R.id.iv_image);


            convertView.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) convertView.getTag();
        }

        viewHolder.tv_foldern.setText(al_menu.get(position).getStr_folder());
            viewHolder.tv_foldersize.setText(al_menu.get(position).getAl_imagepath().size()+"");



        Glide.with(context).load("file://" + al_menu.get(position).getAl_imagepath().get(0))
                .diskCacheStrategy(DiskCacheStrategy.NONE)
                .skipMemoryCache(true)
                .into(viewHolder.iv_image);


        return convertView;

    }

    private static class ViewHolder {
        TextView tv_foldern, tv_foldersize;
        ImageView iv_image;


    }


}
PhotosActivity.java
package galleryimages.galleryimages;

import android.app.Activity;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.GridView;

/**
 * Created by deepshikha on 20/3/17.
 */

public class PhotosActivity extends AppCompatActivity {
    int int_position;
    private GridView gridView;
    GridViewAdapter adapter;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        gridView = (GridView)findViewById(R.id.gv_folder);
        int_position = getIntent().getIntExtra("value", 0);
        adapter = new GridViewAdapter(this,MainActivity.al_images,int_position);
        gridView.setAdapter(adapter);
    }
}
GridViewAdapter.java
package galleryimages.galleryimages;

/**
 * Created by deepshikha on 3/3/17.
 */

import android.app.Activity;
import android.content.Context;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;

import com.bumptech.glide.Glide;
import com.bumptech.glide.load.engine.DiskCacheStrategy;


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


public class GridViewAdapter extends ArrayAdapter<Model_images> {

    Context context;
    ViewHolder viewHolder;
    ArrayList<Model_images> al_menu = new ArrayList<>();
    int int_position;


    public GridViewAdapter(Context context, ArrayList<Model_images> al_menu,int int_position) {
        super(context, R.layout.adapter_photosfolder, al_menu);
        this.al_menu = al_menu;
        this.context = context;
        this.int_position = int_position;


    }

    @Override
    public int getCount() {

        Log.e("ADAPTER LIST SIZE", al_menu.get(int_position).getAl_imagepath().size() + "");
        return al_menu.get(int_position).getAl_imagepath().size();
    }

    @Override
    public int getItemViewType(int position) {
        return position;
    }

    @Override
    public int getViewTypeCount() {
        if (al_menu.get(int_position).getAl_imagepath().size() > 0) {
            return al_menu.get(int_position).getAl_imagepath().size();
        } else {
            return 1;
        }
    }

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


    @Override
    public View getView(final int position, View convertView, ViewGroup parent) {

        if (convertView == null) {

            viewHolder = new ViewHolder();
            convertView = LayoutInflater.from(getContext()).inflate(R.layout.adapter_photosfolder, parent, false);
            viewHolder.tv_foldern = (TextView) convertView.findViewById(R.id.tv_folder);
            viewHolder.tv_foldersize = (TextView) convertView.findViewById(R.id.tv_folder2);
            viewHolder.iv_image = (ImageView) convertView.findViewById(R.id.iv_image);


            convertView.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) convertView.getTag();
        }

        viewHolder.tv_foldern.setVisibility(View.GONE);
        viewHolder.tv_foldersize.setVisibility(View.GONE);



        Glide.with(context).load("file://" + al_menu.get(int_position).getAl_imagepath().get(position))
                .diskCacheStrategy(DiskCacheStrategy.NONE)
                .skipMemoryCache(true)
                .into(viewHolder.iv_image);


        return convertView;

    }

    private static class ViewHolder {
        TextView tv_foldern, tv_foldersize;
        ImageView iv_image;


    }


}
Model_images.java
package galleryimages.galleryimages;

import java.util.ArrayList;

/**
 * Created by deepshikha on 3/3/17.
 */

    public class Model_images {
    String str_folder;
    ArrayList<String> al_imagepath;

    public String getStr_folder() {
        return str_folder;
    }

    public void setStr_folder(String str_folder) {
        this.str_folder = str_folder;
    }

    public ArrayList<String> getAl_imagepath() {
        return al_imagepath;
    }

    public void setAl_imagepath(ArrayList<String> al_imagepath) {
        this.al_imagepath = al_imagepath;
    }
}
AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="galleryimages.galleryimages">

    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"></uses-permission>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <activity android:name=".PhotosActivity"></activity>
    </application>

</manifest>
ADD THIS DEPENDENCY IN YOUR PROJECT:
compile 'com.github.bumptech.glide:glide:3.7.0'
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